The London Encyclopædia: Part I. The Theory of Dyeing.

The London Encyclopædia: Part I. The Theory of Dyeing.

Kappale teoksesta:

The London Encyclopædia, or Universal Dictionary of Science, Art, Literature, And Practical Mechanics, Comprising A Popular View of The Present State of Knowledge.

By The Original Editor of The Encyclopædia Metropolitana, Assisted By Eminent Professional And Other Gentlemen.

In Twenty-Two Volumes

Vol. VII

Printed For Thomas Tegg, 73, Cheapside;
R. Griffin & Co., Glasgow; Tegg and Co., Dublin; Also J. & S. A. Tegg, Sydney and Hobart Town.


Part I. The Theory of Dyeing.
s. 573-593

DYE, v.a. & n.s.
DYER, n.s.
Sax. deagan, to color.
Often written die. To tinge; color; stain.

His looke was sterne, and seemed still to threat
Cruell revenge, which he in hart did hyde,
And on his shield Sansloy in blood lines was dyde.
Spenser. Faerle Queene.

It will help me nothing
To plead mine innocence; for that die is on me,
Which makes my whit'st part black.
Shakespeare. Henry VIII

We have dainty works of feathers of wonderful lustre, excellent dies, and many.
Bacon's New Atlantis.

So much of death her thoughts
Has entertained, as died her cheeks with pale.

He (an obstinate man) will rather suffer seld-martyrdom than part with the least sekuple[?] of his freehold[?]; for it is impossible to dye his dark ignorance into a lighter color.

A translator dyes an author, like an old stuff into a sew colour, but can never give it the lustre of the first tincture; as silks that are twice dyed lose their glosses, and never receive a fair color.

The fleece, that has been by the dier stained,
Never again its native whiteness gained

All white, a virgin saint she sought the skies;
For marriage, though it sullies not, it dies.

Darkness we see emerges into light,
And shining suns descend to sahle night:
Even heaven itself receives another die,
When wearied animals in slumbers lie
Of midnight ease; another, when grey
Of morn preludes the splendoar the day.

There were some of very low rank and professions who acquired great estates: cobblers, diers, and shoemakers gave publick shows to the people.
Arbuthnot on Coins.

It is surprising to see the images of the mind stamped upon the aspect; to see the cheeks take the die of the passions, and appear in all the colours of thought.
Collier of the Aspect.

Flowers fresh in hue, and many in their class,
Implore the pausing step, and with their dyes
Dance in the soft breeze in a fairy mass.



1. Dyeing is a chemical art which has for its object the extractng of the coloring particles from such substances as afford them, and transferring them to certain stuffs of wool, silk, cotton, or linen. No art has profited so much from the improvements of modern chemistry as the art of dyeing has; and it cannot be, nor ought it to be forgotten, that while we owe much to the discoveries of our own countrymen, and the application of those discoveries to the useful arts, the art of dyeing is highly indebted to the national operations of the French chemists.

2. The origin of this art seems to be of high antiquite; a circumstance which renders it impossible to say whom or to what it is to be attributed: conjencture, therefore, is all we can pretend to. As most of the materials from which coloring matter is derived are, of themselves, either of dark and disagreeable colors, or else destitute of any particular color, it is probable that, even in the very earlierst ages, the love of


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seventeenth century. Before that period our cloths were sent to Holland, to be dressed and dyed. This however, was probably practised only in the case of particular colors. The dyeing of woollen and silken goods has indeed long since attained a considerable degree of excellence; but the manufactures of cotton, owing to the small attraction of that substance for coloring matters, have been very deficient in this point. Till within these few years, the colors employed in the dyeing of fustians and cotton velvets were few; and even at this day, many of them are fugitive. But it must be allowed that freat improvements have been made within these few years, from the application of chemical principles, ad by a diligent investigation of the nature of coloring substances. There is however still much room for the improvement of the art, but this can only be effected by the practical dyer acquiring chemical knowledge, an acquisition now happily placced within the reach of every dyer who is capable of reading and understanding the English language. It will not be necessary for our present purpose to enter into a minute examination of the various theories that have been advanced of the nature of colors; at the same time it may be proper, before we deduce a general theory of dyeing, to make a few observations on the common properties of coloring substances.

9. In explaining the cause of color, and the nature of coloring particles, two great inconveniences have arisen. First, from an attempt to illustrate the action, which the particles of coloring substances have on the rays of light, in consequence of their density and thickness, without having any means of ascertaining this, and without any regard to the attractions which result from their chemical composition; in comparing the coloring particles to mucilages and resins, from some very faint resemblances; and in attempting to explain their coloring properties by conjectures, formed respecting their component parts, while these properties ought rather to be ascertained by direct experiment than explained by and imaginary composition. It was also departing from true theory, to ascribe to laws purely mechanical, the adhesion of the coloring particles to the substances dyed, the action of the mordants, the difference between the true or durable, and the false or fugitive dyes.

10. Hellot, who has written and excellent treatise on dyeing, seems to have erred on this subject; and Macquer, who was amongst the first who entertained just notions respecting chemical attractions, seems to have been led astray by his ideas. It appears, however, that Dufay had before observed, that the coloring particles were naturally disposed to adhere more or less firmly to the filaments which receive them; and had very justly remarked, that without this disposition, stuffs would never assume any color but that of the bath, and would always divide the coloring particles equally with it: whereas the liquor of the bath sometimes becomes as limpid as water, giving off all the coloring particles to the stuff; which, he observes, seems to indicate that the ingredients have less attraction for the water than for the particled of the wool.

11. Bergman seems to have been the first who referred phenomena of dyeing entirely to chemical principles. Having dyed some wool and some silk in a solution of indigo, in very dilute sulphuric acid, he explains the effects he observed in the operation, by attributing them to the precipitation, occasioned by the blue particles having a greater affinity for the particles of the woold and silk, than for those of the acidulated water. He remarks that this affinity of the wool is so strong, as to deprive the liquor entirely of the coloring particles; but that the weaker affinity of the silk can only diminish the proportion of these particles in the bath, and he shows that on these fidderent affinities depend both the permanence and intensity of the color.

12. This is the true light in which the phenomena of dyeing should be viewed; they are real chemical phenomena, which ought to be analysed in the same way as all those dependent on the actions which bodies exert, in consequence of their peculiar nature. It is evident, that the coloring particles of bodies possess chemical properties, that distinguish them from all other substances; and that they have attractions peculiar to themselves, by means of which they unite with acids, alkalis, metallic oxides, or calces, and some earths, principally alumine or pure clay. They frequently precipitate oxides and alumine, from the acids which held them in solution; at other times they unite with the salts, and form supercompounds which combine with the wool, silk, cotton, or linen. An with these their union is rendered much more close by means of alumine or etallic oxide, than it would be without their intermedium.

13. The difference in the affinity of the coloring particles for wool, silk, and cotton, is sometimes so great, that they will not unite with one of these substances, while they combine very readily with another; thus, cotton receives no color in a bath which dies wool scarlet. Dufay prepared a piece of stuff, the warp of which was wool and the woof cotton, which went through the process of fulling, that he might be certain, that the wool and the cotton receives exactrly the same preparation; but the wool took the scarlet dye, and the cotton remained white. It is tis difference of affinity which renders it necessary to vary the preparation and the process, according to the nature of the substance which is intended to be dyed of a particular color. And these considerations ought to determine the means to be pursued for the improvement of the art of dyeing. It is highly proper to endeavour to ascertain what are the constituent principles of the coloring particles. And in this enquiry, the most essential circumstances are, to determine the affinitied of a coloring substance; forst, with the substances which may be employed as menstrua; secondly, with those which may, by their combinations, modify the color, increase its brilliancy, and help to strengthen its union with the stuff to be dyed; thirdly, with the different agents which may change the color, and principally with the external agents - air and light.

14. The qualities of the uncombined coloring particles are modified when they unite with a substance; and, if this compound united with a stuff, it undergoes new modifications. Thus the


properties of the coloring particles of cochineal are midified, by being combined with the oxide of tin, and those of the substances resulting from this combination are again modified by their union with the wool or silk; so that the knowledge we may acquire by the examination of coloring substances in their separate states, can only inform us respecting the preparations that may be made of them; that which we acquite respecting their combinations with substances which serve to fix them, or to increase their beauty, may inform us what processes in dyeing ought to be preferred or tried; but it is only by direct experiment made with the different substances employed in dyeing, that we can confirm our conjectures, and properly establish the process.

15. These facts show, that the changes produced by acids and alkalis on many vegetable colors, such as the chemists employ, in order to discover the nature of different substances, are owing to the combinations, which take place between these coloring particles and the acids and alkalis. The compounds resulting from these may be compared to neutral salts, which possess qualities different from those of their component parts, but in which one of these parts may be in excess, and its qualities consequently predominant. This state of combination is observable between the coloring particles of cochineal and acidulous tartrite of potassa, or cream of tartar: by evaporating slowly a solution of this salt in a decoction of cochineal, crystals are formed, which retain a fine ruby color, much more bright and intense than that of the liquor which formed them.

16. It was the opinion of Berthollet that some of the acids, particularly the nitric, after combining with the coloring particles, changed the color which they at first produced, making it yellow, and finally destroying it; after which they act by means of one of their principles, viz. the oxygen. But this theory, Dr. Ure remarks, is not now tenable, since it is known that dry chlorine does not blanch dry litmus paper. When moisture intervenes, muriatic acid is formed, and oxtgen evolved; to the action of which body on the color the bleaching effect is to be ascribed. Water is the source of the discoloration, both in the ancient and modern process of bleaching. Blue colors are not the only ones which becoem red by the addition of acids, and green by that of alkalis; most red colors, as that of the rose, for instance, are heightened by acids, and made green by alkalis; and some green colors, such as that of the green decoction of burdock, according to the experiments of Mr. Nose, and the green juice of Mr. Becker, are reddened by acids.

17. This property, which is common to most of the ordinary colors of vegetables, seems to prove that there is a close analogy between their coloring particles; and it is not without foundation, that Linnaeus supposed, that the red in vegetables was owing to an acid, and indicated its presence; but there are also many vegetables which contain acid in a disengaged state, without their possessing a red color. It is therefore evident, that the coloring particles have affinities for acids, alkalis, earths, and metallic oxides...

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advantage is, that the acid liquor, from which alumine is separated, has much less action on the color when it consists of the acetous, than when it consists of a stronger acid, such as the sulphuric. In short, the acetite of alumine not having the property of crystallising, the mordant, which is thickened with starch or gum, to prepare it for being applied to the bloch on which the design is engraved, does not curdle, as it would if it contained alum capable of crystallising. By attending to the operation performed upon a piece of linen cloth, we find, that when it has been impregnated by the mordant, in the manner determined by the design, it is put into a bath of madder; the whole of the cloth becomes colored, but the tinge is deeper in those parts which have received the mordant; there the coloring particles have combined with the alumine and the cotton, so that a triple compound has been formed, and the acetous acid separated from its basis remains in the bath.

Thus the coloring particles, combined with the alumine and the stuff, are much more difficultly affected by external agents, than when they are in a separate state, or combined only with the stuff, without any intermediate bond of union; and on this property the operations, to which the cloth is afterwards subjected, are founded. After it has been maddered, it is boiled with bran, and spread upon the grass; and these operations are alternately repeated until the ground becomes white. The coloring particles, which have not united with the alumine, are altered in their composition, dissolved, and separated, while those that have combined with it remain, and are preserved, without alteration; and thus, the design alone remains colored. It seems that this decomposition of the coloring particles, by exposure on the grass and boiling with bran, is accomplished in the same manner as that of the coloring particles of flaz, and admits of the same explanation. The only difference consists in substituting bran for alkalis, because they would dissolve a part of the coloring matter, which is fixed by the alumine, and would change its color; instead of which, the bran, having a much weaker action on this substance, affects only the coloring particles, which, by the action of the air, have been disposed more easily to solution. If, however, instead of the mordant, a solution of iron be employed, similar phenomena are exhibited. The coloring particles decompose the solution of iron, and form a triple compound with the stuff; but, instead of red, we obtain from the madder, brown colors of different shades, down even to black; and, by uniting these two mordants, alum and iron, we have mixed colors, inclining to red on the one hand, and to black on the other, such as mordoré, and puce color. Other colors are also procured by substituring dyers-weed for madder; and by means of these two coloring substances, indigo, and the two mordants above mentioned, we obtain most of the different shades that are observable in stuffs which are printed.

21. The different substances which enter into the composition of a mordant remain in combination till a new action is induced by the application of another substance. This the affinity of the stuff for one of their constituent parts produces a decomposition and new combinations. But even this effect is sometimes incomplete, or does not at all take place without the action of another affinity, namely, that of the coloring particles. We have an example of this in the mixture of alum and tartar, which is one of the most common mordants in the dyeing of wool.

22. M. Berthollet, having dissolved equal weights of alum and tartar, found that the solubility of the tartar was increased by the mixture. By evaporation and a second crystallisation, the two salts were separated, so that no decomposition had taken place. Half an ounce of alum and one ounce of wool were then boiled together for an hour, and a precipitate was formed, which, being carefully washed, was found to consist of filaments of wool incrusted with earth. To this sulphuric acid was added, and the solution being evaporated to dryness, crystals of alum were produced, with the separation of some particles of carbonaceous matter. The liquid in which the wool had been boiled being evaporated, yielded only a few grains of alum; what remained would not crystallise. This being again dissolved, and precipitated by means of an alkali, the alumina which was thrown down was of a slate color, became black when placed on red-hot coals, and emitted alkaline vapors. From this experiment it appears that the alum was decomposed by the wool, and that part of the alumina had combined with its most detached filaments which were least retained by the force of aggretation; that part of its animal substance had been dissolved and precipitated by the alkali from the tripple compound thus formed.

24. From these experiments it appears, in the first place, that the wool had begun a decomposition of the alum; that it had united with a part of the alumine; and that even the part of the alum which retained its alumine had dissolved some of the animal matter. In the second place, that the tartar and alum, which cannot decompose each other solely by their own affinities, become capable of acting on each other when teir affinities are assisted by that of the wool. And, in the third place, that the tartar appears principally useful for moderating the too powerful action of the alum upon wool, whereby it is injured; for tartar is not used in the aluming of silk and thread, which have less action on the alum than wool has. As the decomposition of alum by the tartar and wool takes place in consequence of affinities which nearly balance each other, and the process must therefore go on slowly, it is useful to keep the stuff impregnated with alum and tartar for some days in a moist


place, as is generally recommended. The final effect of aluming, in whatever manner performed, and whatever chemical changes may have taken place in it, consists in the combination of alumine with the stuff: this union has propably been imperfect, and the acids only partially separated, but becomes complete when the cloth has been boiled with madder, as in the case of printed stuffs. But an acid or an alkali may form a supercompound with the stuff, the coloring matter and the alumine; for there are some colors which are changed by an acid, and restored by alkalis, or by calcareous earths, which take the acid from them, or vice versa; but this supercomposition does not take place with respect to those colors which are esteemed durable, being unchangeable by alkalis or acids, which are not strong enough to destroy their composition.

25. The attraction of alumine for animal substances is not, however, merely indicated by uncertain appearances, nor supposed for the purpose of being employed in explanations, but is proved by direct experiment. M. Berthollet united them together, by mixing an animal substance with a solution of alum: a double exchange took place, the alkali entered into combination with the acid of the alum, and the alumine, combining with the animal substance, was precipitated. He also proved the affinity of alumine for animal substances by another experiment: having mixed a solution of glue with a solution of alum, he precipitated the alumine by an alkali, and the glue with which it had combined fell down along with it. The compound has the appearance of a semitransparent jelly, and dries with difficulty. Thus, in the preceding experiments, the alkali precipitated the alumine combined with the animal substance, from the uncrystallisable residue of the alum which had been boiled with the wool.

26. The affinity of alumine for most coloring substances, may also be shown by direct experiment. If a solution of a coloring substance be mixed with a solution of alum, a precipitation sometimes takes place; but if to the liquor we add an alkali, which decomposes the alum, and separates the alumine, the coloring particles are then precipitated, combined with the alumine, and the liquor remains clear: this compound has obtained the name of lake. In this experiment, too much alkali must not be added, because alkalis are capable of dissolving lakes in general. No direct experiment has however yet shown, that alumine attracts any vegetable substance except the coloring particles: its affinity for them seems much weaker than that which it has for animal substances; hence the acetite of alumine is a better basis for cotton and linen than alum is, and upon this depend the different means employed to increase the fixity of the coloring particles of madder in the dyeing of these substances.

27. Metallic oxides have so great an affinity for many coloring substances, that they quit the acids in which they were dissolved, and are precipitated in combination with them. On the other hand, all metallic oxides have the property of uniting with animal substances; and these different compounds may be formed by mixing an alkali, saturated with an animal substance, with metallic solutions. It is not surprising therefore, that metallic oxides should [---] bond of union between the coloring particles and animal substances; but, vesides the attraction of these oxides for the coloring particles, and for animal substances, their solutions in acids possess qualities which render them more or less [---] act as mordants: thus, those ocides which [---] part with their acids, such as that of tin, are capable of combining with animal substances, without he aid of coloring particles; it is [---] to impregnate the wool or silk with a [---] tin, although they be afterwards carefully [---] which is not the case with other metallic solutions. Some metallic substances afford, [---] combination, only a white and colorless basis; [and?] some by the admixture of their own color, to [---] that which is proper to the coloring [---] but in many metallic oxides, the color [---] according to the proportion of oxygen they contain, and the proportion of this is ieasily fixed. [---] change, Upon these circumstances then properties in dyeing chiefly depend.

28. The affinity of metallic oxides for substances of vegetable origin, seem much [---] than that which they have for animal substances; metallic solutions are, therefore, not well [---] to serve as mordants for colors in cotton or [---] except iron, the oxide of which [---] with vegetable substances, as is shown by [---] moulds, which are owing to a real [---] tion of this oxide. Whenever the coloring particles have percipitated a metallic oxide [---] menstruum, the super [---] liquor [---] disengaged acid, which is commonly capable dissolving a portion of the compound of [---] loring substance and oxide, so that the [---] remains colored; but sometimes the whole [---] coloring particles are precipitated, when the proportions have been accurately adjusted [---] precipitation is faciliated, and render [---] complete, by the presence of the stuff, [---] assists, by the tendency it has to unite [---] compound of oxide and coloring particles. [---] combined metallic oxides have also [---]dent action on many coloring substances [---] boiled with them, and modify their [---] oxide of tin in particular increases the [---] and fixity of many.

29. The compounds of oxides and [---] substances are similar to many other [---] compounds, which are insoluble, when the [prin?]ciples of which they are formed are properly proportioned; but which are capable of [---] supersaturated by an excess of one of [---]ples, and thence of becoming soluble. [---] metallic oxide, united with a coloring substance to excess, produces a liquor, the color of [---] will be modified by the oxides; whereas, [---] the coloring matter is not in excess, the compound will be insoluble, or nearly so; the effects are very evident in the comnination of [---] with the astringent princile. Neural [---] such as nitre, and particularly muriate of soda or common salt, act as mordants, and [---] color; but it is difficult to ascerrain the [---] in which they act. M. Berthollet [---] the muriate of soda was contained , [---] in the pricipitates produces by some [---]


coloring particles, and tost taese precipitates retained a considerable degree of solubility; it would seem that a small part of the salt becomes fixed with the coloring particles and the stuff. Salts with calcareous bases also modify colors; but, as these modifications are nearly similar to those which would be produced by the addition of a small quantity of lime, it is probable that they are decomposed, and that a little of the lime enters into combinaation with the coloring particles and the stuff. By attention to this, we shall easily discern what combinations are formed by the agency of the different reactives, employed in the analysis of coloring substances; but we must not forget, that the mordants and the coloring particles have a mutual action on each other, which may change their properties. It is evident that, by varying the mordants, we may greatly multiply the shades obtained from a coloring substance; even to vary their mode of application may be sufficient: thus we shall obtain different effects by impregnating the stuff with mordant, or by mixing the mordant with the bath; by applying heat, or using exsiccations, for we operate upon three elective attractions; that of the coloring particles, that of the stuffs, and that of the principle of the mordant; and many circumstances which merit further explanation. Exsiccation, or drying, favors the union of the substances which have an affinity for the stuff, and the decompositions which may result from that union; because the water which held these substances in solution, by its attraction, opposed the action of the stuff; but the exsiccation should be slow, in order that the substances may not be separated before their mutual attractions have produced their effect.

30. Considerable differences must be observed in the manner of employing the mordant, as the force of affinity between the stuff and the coloring matter is greater or less. When this affinity is strong, the mordant and the coloring substance may be mixed together; the compound thus formed, immediately enters into combination with the stuff. But, when the affinity between the stuff and the coloring particles is weak, the compound formed on the latter and the mordant may separate, and a precipitation take place, before it can be attached to the stuff; and hence it is, that the mordant which is to serve as the medium of union between the stuff and the coloring matter, must be combined with the former, before the application of the latter. It is from these differences hat different processes must be followed in fixing coloring matters on animal and vegetable productions.

31. In judging of the effects of mordants, and the most advantageous manner of applying them, it is necessary to attend to the combinations which may be formed, either by the action of the ingredients of which they are composed, or by that of the coloring matter and the stuff. It is necessary, also, to take into consideration the circumstances which may send to bring about these combinations with more or less rapidity, or that may render them more or less perfect. The action which the liquor in which the stuff is immersed may have, either on its color or texture, must also be considered; and to be able accurately to judge of the extent of this action, we must know the proportions of the principles of which the mordant is composed; which of these principles remains in an uncombined state in the liquor, and the proportion or quantity which is separated.

32. The coloring particles have been hithern considered only as substances capable of forming different combinations, by which their properties are modified; but they may be altered in their composition, either by other external agents, or by the substances with which tjey unite. The stability of a color consists in its power of resisting the action of vegetable acids, alkalis, soap, and more especially that of the air and light; but this power varies exceedingly, according to the nature of the color and the species of the stuff; for the same durability is not required in the colors of silk as in those of wool. There is not much obscurity in the action of water, acids, alkalis, or soap: it is a solution brought about by these agents: and it appears that a small quantity of acid, or of alkali, sometimes unites with the compound which gives the color; because the color is not destroyed, nut only changed, and may be restored by taking away this acid; for instance, by chalk and ammoniac, or volatile alkali. But this is not the case with respect to the action of air and light.

33. Scheele observed, that the oxygenated muriatic acid rendered vegetable colors yellow, and he attributed that effect to the property it had of taking up the phlogiston which entered into their composition. Berthollet has shown, that the properties of the oxygenated muriatic acid were owing to the combination of its oxygen with the substamces exposed to its action; that it commonly rendered the coloring particles yellow; but that, ny a continuance of its action, it destroyed their color: without determining in what this action consisted. Fourcroy afterwards made several observations on the action of oxygen on the coloring particles, which throw a great deal of light on the nature of the changes they undergo, chiefly when watery solutions of them are left exposed to the air, or have been subjected to a boiling heat. He observed that, in consequence of theaction of the air, vegetable decoctions formed pellicles, which lost their solubility, and underwent successive changes of color; he marked the gradations of color thus produced, and concluded, from his observations, that oxygen entered into the composition of the coloring particles; that when it combined with them, their shade was changed; that the more they received, the more fixed did their color become; and that the best method of obtaining permanent unchangeable colors, for painting, was to choose such as had been exposed to the action of the oxygenated muriatic acid.

34. in considering the effects of air on colors, it is necessary to make a distinction between those produced by metallic oxides, and those produced by the coloring particles. Berthollet is of opinion that the modifications of the former are entirely owing to different proportions of oxygen, but from observation he has been led to


form a different opinion respecting the modifications of the latter. He observed, that the oxygenated muriatic acid exhibited different phenomena with the coloring particles; that sometimes it discharged their colors, and rendered them white; that most frequently it changed them to a yellow, fawn, or root-colored, brown, or black, according to the intensity of its action; and that, when their color appeared only discharged or rendered white, heat, or a length of time, was capable of rendering them yellow. He compared the effect produced by the oxygenated muriatic acid, when the particles are rendered yellow, fawn-colored, or brown, with the effect of a slight degree of combustion, and showed that they were the same; that they were owing to the destruction of the hydrogen, which, combining with the oxygen, more easily, and at a lower temperature than charcoal does, leaves it predominant, so that the natural color of charcoal is more or less blended with that which before existed. This effect becomes very evident, when sugar, indigo, or the infusion of the gall-nut, or of sumach, are exposed to the action of oxygenated muriatic gasM the sugar and the indigo assume a deep color, and afford indisputable marks of a slight combustion; the infusion of the gall-nut, and that of sumach, let fall a precipitate, which is not far from being pure charcoal or carbon. These appearances are analogous to those which are observed in the distillation of organised substances; in proportion as the hydrogen is extracted in the form of oil, or of gas, the substance grows yellow and at lenght there remains only a black coal. If the hydrogen be expelled from an oil, by heat, it grows brown, evidently in the same way.

35. Berthollet also found, by other experiments made on alcohol and ether, that the oxygen united to the marine acid, had the property of combining with the hydrogen, which abounds in these substances, and of thereby forming water. He therefore supposes, that when the oxygenated marine acid renders a color yellow, fawn-colored, or brown, the effect proceeds from the coloring matter having undergone a slight combustion, by which more or less of its hydrogen has been converted into water; and that the charcoal, thus rendered predominant, has communicated its own color. The art of bleaching linen by means of the oxygen of the atmosphere, of the dew, and of the oxygenated marine acid, he also supposes to depend on this change of the coloring matter. The coloring particles of the flax are rendered soluble in the alkaline lixividia, the action of which ought to be alternate with that of the oxygen. These coloring particles may be afterwards precipitated from the alkali, and by evaporation and drying become black, and prove the truth of this theory, both by the color they have acquired, and by the quantity of charcoal which they yield on being analysed. But the alkaline solution of the coloring matter of linen which is of a dark brown color, loses its color almost entirely, by the addition of certain quantity of oxygenated muriatic acid; and the same effect is observable in many other substances, which have assumed a color originating from a commencement of combustion. A piece of linen, which appears white, may grow yellow in process of time, particularly if exposed to a certain degree of [...] oxygenated parts have not been [...] sufficientyly strong lixivium. In the [...]ner , the green parts of vegetables [...] white by the oxygenated muriatie[...] become yellow when boiled.

36. From these facts it appears, [...] is capable of whitening, or rendering [...] coloring matters with which it unit[...] by having produced the effects of [...]bustion upon them; or possibly these place only afterwatds in a gradual [...] more rapidly, when the whole is [...] certain degree of heat. It is extreme [...] that in all cases a part of the oxygen [...] the coloring matter, without being [...] with the hydrogen in particular, and [...] this way that oxygen acts, in rendering [...]ing matter of flex more easily soluble [...]. In many other cases oxygen has [...] influence on the changes which take [...] coloring particles of vegetables; the [...] are formed chiefly in the leaves, [...] inner bark of the trees; by degrees they [...] slight combustion, either from the [...] atmospheric air which surrounds [...] that of the air which is carried by a [...] of vessels into the internal parts of ve[...].

37. Berthollet, therefore, suppose[...] explain how the air acts upon colori[...] of an animal, or a vegetable nature; [...]bines with them, renders them weake[...] and by degrees occasions a slight [...] by means of which the hydrogen [...] into their composition is destroyed; [...] to a yellow, ed, or fawn-color; the[...] for the styff seems to diminish; th[...] from it, and are carried of by water [...] effects vary, and take place more or [...] and more or less completely, acco[...] nature of the coloring particles; or [...] the nature of the properties which [...] in the state of combination into whic[...] gone. The changes which orccur in [...] produced by the union of the colori[...] with metallic oxides, are effects com[...] the change which takes place in [...] particles, and of that which is underg[...] metallic oxide.

38. The light of the sun considers [...] rates the extinction of colors. It [...]fore, if this theory be well founded, [...] combination of oxygen, and the [...] thereby induced. Sennebier, who [...] many interesting observations on th[...] light on different substances, and part[...] their colors, attributes these effects [...] combination of light with the substan[...] the effects of light on the color of [...] long ago been noticed; it preserves [...] appearance while kept in the dark, [...] exposed to the light, it becomes yellow[...] or of other shades. The same [...] marked the varieties which occur in [...]lar in different kinds of wood, and [...] the changes are proportioned to the [...] of the light, and that they take place [...] water, but that wetted wood under [...] changes less quickly than that which [...]


that several folds of riband were required to defend the wool completely, that a single leaf of black paper was sufficient, but that, when paper of any other color was substituted, the change was not prevented; a single covering of white paper was insufficient, but two intercepted the action of the rays of light.

39. He extended his experiments to a great number of vegetable substances, in a manner that may serve to illustrate different phenomena of vegetation. If a well-made solution of the green parts of vegetables in alcohol, which has a fine green color, be exposed to the light of the sun, it very soon acquires an olive hue, and loses its color in a few minutes. If the light be weak, the effect is much more slow; and in perfect darkness, the color remains without alteration, or, if nay change does take place, it requires a great lenght of time. An alkali restores the green color; but if the change of color in the liquor has been completed, the alkali has no effect. No change of color takes place in azotic gas, nor in a bottle which is exactly full. A bottle half full of this green solution was inverted over mercury, by Berthollet, and exposed to the light of the sun; when the color was discharged, the mercury was found to have risen in the bottle, and consequently vital air had been absorbed, the oxygen having united with the coloring matter. The precipitate which M. Sennebier mentions was not evident; the liquor had continued transparent, and retained a slight yellow tinge. On evaporating this liquor, its color was immediately rendered darker, and became brown; the residuum was black, and in a carbonaceous state.

40. Light, therefore, acts by favoring the absportion of oxygen, and the combustion of the coloring matter. At first, the marks of combustion are not evident; the liquor retains only a a slight yellow tinge; but, by the assistance of heat, the combustion is completed, the liquor becomes brown, and leaves a black residuum. If the vessel which holds the liquor contains no oxygen gas, the light has no effect on the coloring matter; azotic gas in this situation suffers no diminution. The observation, that ribands, or a single leaf of white paper, do not prevent the action of light, deserves attention, as it shows that light can pass through coverings which appear to be opaque, and exert its energy a considerable septh within. Beccaria and Sennebier have compared the effects of light on ribands of various colors; but the differences they have observed are rather to be attributed to the nature of the coloring matters, than to the colors; for a riband dyed with Brasil-wood will lose its color much sooner that one dyed with cochineal, though the shade should be exactly the same in each.

41. Although light greatly acceletares the combustion of the coloring particles, and seems even necessary for their destruction in some cases, in other it is not required. It was found, by puttingsome plants into a dark place, in contact with vital air, that that air was absorbed by some of them; and, also, that the rose suffers a change, and becomes of a deeper hue, when it is not in contact with vital air, probably because it contains a little oxygen, the combination of which then becomes more intimate. But many flowers when in azotic gas, retain their color in perfection. The ticture of turnsole was placed in contact with cital air over mercury, both in the dark, and exposed to the light of the sun; the former continued unchanged for a considerable length of time, and the vital air had suffered no diminution; the other lost much of its color; became red; and the air was, in a great measure, absorbed, and a small quantity of carbonix acid was produced, which undoubtedly had occasioned the alteration of color from blue to red. From this we may form an idea of some of the changes of color, produced by a particular disposition of the component principles of vegetavle substances, when, by their combination with oxygen, they undergo the effects of a slight combustion, which may generate an acid, as in the leaves in autumn, which grow red before thet become yellow, and in the streaks which are seen in flowers, the vegetation of which is becoming weak.

42. On the whole it is evident, that coloring substances resist the action of the air more or less, according as they are more or less disposed to unite with oxygen, and thereby to suffer more or less quickly a smaller or greater degree of combustion. Light favors this effect, which in many cases is not produced without its assistance; but the coloring matter, in its separate state, is much more prone to this combustion, than when united to a substance, such as alumine, which may either defent it by its own power of resisting combustion, or, by attracting it strongly, weaken its action on other substances, which is the chief effect of mordants. This last compound acquires still greater durability, when it is capable of combining intimately with the stuff upon which it is deposited. Thus the coloring matter of cochineal is easily dissolved in water, and its color is quickly changed by the air; but when brighter, and almost insoluble in water, though it is still easily affected by the air, and by oxygenated muriatic acid; it resists the action of these better, however, when it has formed a triple compound with a woollen stuff. But still it is not to be inferred, that all yellow colors are owing to the same carbonaceous part of the coloring substance; very different compounds are capable of producing the same colors; thus, indigo is very different from the blue of our flowers, from that of oxide of copper, and from that of Prussian blue. Berthollet does not even suppose, that oxygen may not unite in a small proportion with some coloring substances, without weakening their color, or changing it to yellow. Indigo becomes green by uniting with an alkali, with lime or a metallic oxide; but resumes its color, and quits these substances, when it recovers a small portion of the oxygen which it had lost. The liquor of the whelk, employed to dye purple, is naturally yellowish; but when exposed to the air, and more especially to the sun, it quickly passes through various shades, and at length assumes the exquisite purple color of the ancients; and which, according to the testimony of Eudecià, derived its lustre and perfection from exposure to the sun's rays.

43. It may the be considered as a general


fact, that colors become brighter by their union with a small portion of oxygen. It is on this account found necessary to air stuffs when they come out of the bath, and sometimes even to take them out of it from time to time, expressly for this purpose; but the quantity of oxygen which, thus becoming fixed, contributes to the brughtness of the color, is very considerable in some cases and the deterioration of shade soon begins. But the action of the air affects not only the coloring matter and the stuff, but also metallic oxides, which have at first been deprived of a part of their oxygen by the coloring particles, may absorb it again. Those then, the color of which varies according to their proportion of oxygen, have thereby an influence in effecting the changes which the stuff undergoes. It is undoubtedly to this cause that the change observable in the blue given to wool, by sulphate of copper, of blue vitriol, and logwood, is to be attributed. The blue soon becomes green by the action of the air: now copper, which has a blue color, when combined with a small proportion of oxygen, assumes a green one by its union with a larger quantity. The change which the coloring particles undergo, may indeed contribute to this effect; but the coloring particles of the logwood, which have themselves a dark color, should rather become brown by combustion, than grow yellow, which would be necessary in order to produce a green with the blue. It has been observed, that coloring particles in a state of combination were less disposed to be changed by the action of the air, than in an uncombined state. This is generally the case, but there are some exceptions; an alkali, for instance, produces a contrary effect. A matrass half filled with an infusion of cochineal, was exposed to the light, over mercury; a similar matrass contained an infusion of cochineal made with a little tartar; and in a third, a small quantity of alkali had been added to the infusion. The second matrass appeared least altered in the same space of time, and in it the absorption had been least considerable. IN the third, the color of the liquor became first brown, and was then discharged; and the absorption of air, though inconsiderable, was greater than in the two others. On evaporation it assumed a brown color; and left a residuum of a yellowish brown.

44. Similar experiments having been made on different coloring substances, the alkali was found to darken their color, which grew more and more brown, and promoted the absorption of air. Madder appeared to be the only exception to this rule: its color, which became darker at first, stood better than that of the infusion made without alkali. The general effect of alkalis on the coloring particles is consonant to that which it produces on many other substances, such as sulphur; it favors the absortion of air, because it has a strong affinity for the substamce which is the result of absorption. From this effect of alkalis, a fact which has been observed by Becker may be explained; viz. that a vegetable infusion, rendered green by an alkali, becomes gradually yellow, if left exposed to the air, and that when the yellow is completely formed, acids cannot restore the original color: but that is not the case, when a vegetable color, reddened by an acid, has been kept in like manner for some time. Those instances in which acids have been employed, which act by giving off their oxygen, must be excepted, for in these there is and extraction of color.

45. From the above remarks on mordants it must appear very obvious that the practical dyer ought to be exceedingly careful in his selection of substances, giving the preference to those that most readily resist the action of the causes what we have specified.

46. It may not be improper to notice the action of these acids on animal substances, [...] consequence of its intimate connexion with the subject of mordants. It was observed by M. Brunwiser, that wood, on being exposed to the action of the air, assumed different color: this led him to endeavour to ascertain whence those colors arose, and to produce them by artificial means. He remarked that on moisten[...] the surface of wood, particularly young wood, with nitric acid, it assumed a yellow color; and that, by applying in the same way the muriatic and sulphuric acids, the wood assumed a violet color. Hence he inferred that, as all colors are produced by a mixture of yellow, blue, and red, all those colors which are seen in the leaves, fruits, and flowers of trees, are owing to the coloring particles which exist in the wood, and are there kept in a state of disguise, by the ar[...] of an alkali; that the mineral acids, by taking [...] this alkali, set the coloring particles at liberty; and that the fixed air, by penetrating the leaves, fruits and flowers, produces naturally the same effect by combining with the alkali which kept them disguised.

47. M. de la Folie informs us that having immersed a skein of white silk in nitrous acid of the strength generally used in commerce, the silk in three or four minutes assumed a fine jonquilie yellow. He washed it several times in water, that it might not be affected by any [...] acid; the color sustained several trials to [...] he submitted it, and the silk preservet its [lustre?] unimpaired. When dipped into an alkaline solution, a fine orange color was the result. Dr. Gmelin observes, that he has given a fine brunstone color to silk, by keeping it for a day in cold nitric acid, or some hours only, when the acid was warm. Boiling with soap and water [...]nished the brightness of this color; and it was changed to a fine lemon color, by being kept for twelve hours in an alkaline solution; but, when the solution was employed hot, a fine gold coke was produced. The different solutions of metals in nitric acid communicated a more or less deep yellow to silk, as did also the solution of alumine in the same acid; but those of the calcareous earth and magnesia had no effect whatever.

48. M. Berthollet also found, that the oxygenated muriatic acid has the property of [...] animal substances yellow; but that it does not give them so deep a color as the nitrous acid, and it weakens them much more than that acid when properly diluted; so that the nitrous acid is far preferable for the different purposes of art. It, therefore, appears that the nitrous acid, diluted with a certain quantity of water, gives [...]


a yellow color, which is more or less deep, according to the concentration of the acid, its temperature, and the time of immersion; that the silk must be carefully washed as soon as taken out of the acid; that this color possesses considerable brightness; and that it may be made deep without sensibly weakening the silk, which may render the process really useful. The color may also be modified by the use of alkalis. The solutions of calcareous earth and magnesia produce no effect upon silk, because they do not contain an excess of acid; but the solutions of alumine and of all metallic substances, produce a more or less deep yellow, because they all contain more or less excess of acid, which acts upon the silk like uncombinet acid.

49. It appears likewise to have been the acid alone that dyed the animal substances yellow, in the experiments of M. Brunwiser, and not the matter extracted from the wood, as he supposed. Nor is the yellow color in these cases owing to iron, as De la Folie suposed; for the purest nitrous acid, which contains no iron, produces it, as well as that in which the presence of that metal may be supposed to exist. Silk, when put into concentrated nitrous acid, quickly assumes a deep yellow color, loses its cohesion, and is dissolved; during this solution, the azote, which enters into the composition of animal substances, is extricated, with a long continued effervescence; if the heat be applied, it expels much nitrous gas, and the liquor immediately acquires a deep color and grown brown. At this time, the oxygen of the nitric acid combines with the hydrogen which abounds in animal substances, forming the oil which is obtained from them by distillation, and which renders them so inflammable. When the acid begins to act and to render the silk yellow, the same effect should also begin to take place. M. Berthollet therefore supposes, that the yellow color arises from a commencement of combustion; but that this combustion being very slight, does not sensibly weaken the silk; if, however, the acid be a little too strong, or the immersion too long continued, or if the whole of it be not carried off by careful washing, the silk immediately becomes weak, and is burst. It is, therefore, evident why the nitrous acid is preferable in this operation to that which is saturated with nitrous gas; for, in the former, the proportion of oxygen being greater, it is better fitted to procedure the effects of combustion, than it becomes in the state of nitrous acid. The same explanation ought to apply to the action of the oxygenated muriatic acid on animal substances; it differs, however, in some essential circumstances, which are not easily explained.

50. Silk has been observed to receive a yellow color when the oxygenated muriatic acid is employed, which is much lighter than when the nitrous acid is made use of; the sulphurous acid discharges it in a great degree, but has no effect on the yellow produced by the diluted nitrous acid. The oxygenated muriactic acid has, however, a much stronger action on the silk; it soon weakens, and even dissolves it; and if it be left for some time in this fluid, the yellow which at first appeared grows lighter, agreeably is what has already been remarked, that oxygen, by accumulation, is capable of disguising the yellow color occasioned by the combustion, which it had originally induced. Berthollet has endeavoured to explain the effects which the sulphurous acid produces on colors, by the facility with which it gives off its oxygen, and has compared them to those of the oxygenated muriatic acid; but, although it be true that oxygen adheres much more weakly to the sulphurous than to the sulphuric acid, he does not believe that that explanation is founded in truth.

51. It appears from the observation of De la Folie, that roses, whitened by the vapor of burning sulphur, become green in an alkaline lixivium, and red in acids; and M. Berthollet has himself observed, that the sulphurous acid reddened the tincture of turnsole, which has a very fading color, but that it acted only like other acids, on infusions of fustic, Brasil-wood and logwood; and further, that silk which has been exposed to the vapor of sulphur, exhaled the smell of sulphurous acid, when moistened with sulphuric acid, although it could not be perceived before that odor existed. He therefore supposes, that the sulphurous acid commonly unites with the coloring particles, and with the silk, without giving off its oxygen to them, and consequently without producing any combustion; that the product of that combination sometimes loses its color entirely, which is probably owing to the semi-elastic state of the oxygen; but sometimes combustion may, and even sommonly should take place by degreen, so that the coloring particles, which have been disguised for some time, ought ultimately to leave a yellow color.


52. Astringents deserve particular attention, not only from their great use of dyeing, but as possessing a property common to many vegetables. Perhaps, says Berthollet, there is no property in vegetables concerning which such vague ideas have been currently received. A slight relation in taste has frequently been deemed enough to rank them in the class of astringents; and every substance has been commonly regarded as astringent, or acerb, which turned a solution of iron black. This effect has been presumed to arise from one identical principle residing in all the bodies that produce it. Experience has subsequently shown, that two species of astringents ought to be admitted, vix. tannin and gallic acid. the gallic acid is obtained from gallnuts, in which it is found in great plenty.

53. The gall-nut is an excrescence found on the young branches of the oak, and produced by the puncture of an insect. Fidderent kinds of the gall-nut are met with, some inclining to white, yellow, green, brown, or red; others, ash-colored or blackish. They also differ greatly in magnitude, and are either round or irregular, heavcy or light, smooth or covered with protuberances. Those which are small, blackish, knotted, and heavy, are the best; and are known by the name of Aleppo galls. These astringent substances are almost totally soluble in water by long ebullition. Sixteen drachms afforded Neumann fourteen of extract; from the remaining two drachms, only four grains could be extracted


by alcohol. And the same quantity reated first with alcohol, and then with ater, afforded twelve drachms and two scruples of spiritous extract, and four scruples of watery extract; the residuum weighed hald a scruple more than in the preceding experiment. In the spiritous extract, the taste is more strong and disagreeable than in the watery extract.

54. Many other very interesting observations have been made on astringent substances, by Messrs. Scheele, Monnet and Berthollet. The latter seems to have proved, that it is not the gallic acid which communicates the astringent propertied to the substances that posses it; that the acid itself possesses a high degree of astringency; walnut peels, treated in the same way, do not afford any. The property which the infusion of common galls has, of reddening certain vegetable color, appears to proceed only from the gallic acid. The infusions of sumach, or of sloe-bark, which very readily produce a black precipitate, that of walnut-tree bark, or of quinquina, did not exhibit this property; and thence it is ecident, that the gallic acid does not exist in white galls; for the infusion of these, though it deposit a copious sediment on exposure to the air, is not the gallic acid.

55. If the astringent property were owing to an individual principle distributed in different vegetables, the precipitates obtained by their means, from a solution of iron, would constantly from the same compounds, and exhinit the same appearences and properties; but the precipitate produced by galls is of a blackish blue; that by logwwood has a different shade of blue; that by oak is a fawn color, or blackish brown; that by quinquina, a blackish green. They fall down with different attendant circumstances, and when fixed on stuffs, are discharged by alum and tartar, some much more easily than others; and propably, by multiplying experiments, many other remarkable differences may be discovered in the properties of these different precipitates. Astringents form with iron different species of compounds, and consequentrly do not derive their properties from one principle; but there must be a property common to different substances, to enable them to act uniformly on solutions of iron, and to produce precipitates more or less black, and thus appearing of the same nature.

56. The metallic oxides, which unite with the coloring particles, modify their colors; but some metallic oxides, and particularly that of iron, have colors which vary according to the quantity of oxygen they contain. Iron, when united with only a small quantity of oxygen, has a black color. If any substance, by uniting with the oxide of iron, had the property of taking from it a part of the oxygen, which it has when precipitated from its solution in an acid, this would be sufficient to give it a black color; and if the peculiar color of this substance were not predominant, or of itself inclining to black, the compound formed would have a black cfolor; thus nitrous gas, either uncombined or weakly attracted to nitrous acid, renders solutions of iron [...] and even precipitates the metal, by depricving [...] a portion of its oxygen. By acting in the same manner, ammoniac produces a black preciptate with the solutions of iron; in this case, the nitrogen of the ammoniac form water, by combing with the oxygen that is disengaged from the oxide of the iron. Galls precipitate [...] silver from their solutions, by reduicing [...] their metallic state; they therefore have [...] proterty of sepatrating the oxygen from [...] metals, to which it adheres but slightly [...] from others, that portion which is retained [...] weakest degree. Any infusion of galls, of [...] readily assumes a deep brown color, by exposure to the air; though it absorbs but a small [...] of vital air. The infusion of sumacn, and [...] of woods and barks, also acquire of dark [...] by exposure to the air; so that when [...] upon the oxide of iron, by separating a [...] its oxygen, an astringent ought itself to [...] darker color, by which the black should be [...] .

57. Various substances, which have in [...] respects different properties, produce black [...] solutions of iron. Among these, some are [...] coloring particles, and employed as such it [...]. Logwood, and even most kinds of coloring particles, form brown or blackish precipitation with iron. Sometimes the aspringent effect is not instantaneous; the color of the precititate [...] at first light; it grows deeper gradually, [...] darkened in proportion as the iron loses its oxygen. The infusion of fustic produces [...] the solution of iron, a yellow precipitate, [...] grows brown by degrees, and becomes black after a considerable time. But through the property of precipitating solutions of iron black does not indicate the presence of the same individual principle in the substances which posses it, there can be no inconvenience in calling [...] the name of astringent, provided by that [...] meant only a property, which is common to a great number of substances, and which [...] have in various proportions.

58. The astringent principle is found to precipitate iron from all acids. The acids of phosphorus and arsenic only have stronger [...] than it has for iron. The phosphoric acid was known to have the property of separation [...] from the sulphuric acid; but all acids, except the acetous, and propably some other vegetable acids which have not been tried, redissolve the precipitate, and make the color disappear, until they are saturated with an alkali. It is not surprising that the astringent principle can unite with metallic oxides, without having the qualities of an acid; for animal substances, oils, even alkalis and lime, have this property. It is well known, that it is the precipitate composed of iron and the astringent principle, which, by remaining suspended in the liquor, forms ink.

59. But although chemists considered the astringent principle as always the same, experience shows, that all astringent substances are not equally proper for producing a beautiful and durable black; it is of importance to [...] which of them may be employed with the [...] success; it is, however, very difficult to [...]


comparative experiments on this subject with perfect accuracy, because some substances require much longer boiling than others to extract their astringency; because a difference in their coarseness or fineness, when subjected to ebullition, is sufficient to produce differences in the results; and because the coloring particles have a greater or less disposition to combine with the stuff, according to the proportion of sulphate of iron that has been made use of. Solutions of iron in different acids may produce differences in the results, according as the proportion of that metal is greater or less, and according to the degree of strength which the different acids, when disengaged, are capable of exerting on the newly-formed compound.

60. In the dyeing of stuffs also some differences will be found to arise from their greater or less attraction for the coloring particles. Dr. Lewis has proved in his excellent observations on the process of making ink, that no known astringent, non even sumach, can be substituted for gall-nuts. If, says M. Berthollet, too large a proportion of sulphate of iron be added to the galls, the ink becomes speedily brown, and then passes to yellow, because the astringent is destroyed by the action of the oxygen, which the sulphate of the iron affords, or progressively attracts from the atmosphere; for we see that oxygen eventually destroys those coloring substances with which it is combinet in too great quantities. When this accident happens from age, Dr. Lewis found that an infusion of galls passed over the faded characters restored them. According to Dr. Ure, the besy restorative for faded writing is a solution of ferroprussiate of potash, faintly acidulated, or sulphuretted hydrogen water. Dr. Lewis ascertained, by repeated experiments, that the best proportion for ink is three parts of gall-buts to one of sulphate of iron; that cherry-gum, and plum-tree fum, are as good as gum-arabic for giving the necessary consistence, and for keeping suspended the black molecules which tend to fall; and that decoction of logwood employed instead of water for the infusion of the galls improves the beauty of the ink.

61. Mr. Beunie made many experiments to determine the best process for giving cotton a durable black. He first tried what solution of iron gave the finest black to galled cotton; he afterwards combined different solutions, and examined the durability of the blacks which he produced; and made the same experiments on galled cotton, with other metals and semimetals; he employed in like manner a great number of astringets, and tried with them cotton which had received different preparations. He found that out of twenty-one species of astringents, oak saw-dust, the galls of the country, and yellow myrobolans, were the only substances which produced a fine black, but which was still neither so fine nor so durable as that obtained by the common galls. He also found that the oak saw-dust is preferable to the bark, employed by the dyers of thread, and, being cheaper, may be substituted with advantage.

62. Messrs. Lavoisier, Vandermonde, Fourcroy, and Berthollet, made experiments on galls, oak-bark, raspings of heart of oak, the external part of oak, of logwood, and sumach, for the purpose of forming a comparison of their qualities. To ascertain the portion of astringent principle contained in these different substances, they took two ounces of each separately, which they boiled half an hour in three pounds of water; after the first water they added a second, which underwent a similar ebullition; and continued these operations until the substances appeared exhausted: they then mixed together the decoctions that had been successively obtained. A transparent solution of sulphate of iron, in which the proportions of water and sulphate had been exactly determined, was used. They first estimated the quantity of the astringent principle, by the quantity of sulphate which each liquor could decompose, and afterwards by the weight of the black precipitate which was formed. In order to stop precisely at the point of saturation, they proceeded very slowly in the precipitation, and towards the end added the solution of sulphate only drop by drop, and ceased at the moment when the last added quantity no longer augmented the intensity of the black color. When the liquor is too ppaque to allow its shade of color to be distinguished, a small quantity of it is largerly diluted with water, and, by adding to this a little of the solution of sulphate of iron at the end of a glass tube, it is discovered whether or not the point of saturation has been attained: if we then wish to get tje precipitate which is formed, the whole must be diluted with water very copiously.

63. This operation is an easy and accurate mode for manufactures to determine the proper proportions of astringents, and solutions of iron. To saturate the decoction of two ounces of galls, three drachms and sixty-one grains of iron were required; the precipitate weighed seven drachms and twenty-four grains, when collected and dried. The color of the decoction of oaf bark is a deep yellow; a very small portion of sulphate of iron gives it a dirty reddish color, and a larger one changes it to a deep brown. The quantity of sulphate required to saturate the decoction of two ounces of this bark, was eighteen grains. The precipitate, collected and dried, formed coarser and more compact grains, and weighed twenty-two grains; the inner bark of the oak afforded nearly the same result. But the decoction of the raspings of the heart of oak required for its saturation one drachm and twenty-four grains and the precipitate weighed one drachm and twenty-four grains; the decoction of the external wood of the oak, produced very little precipitate. The decoction of the sumach acquired a reddish violet color, when a small quantity of the sulphate of iron was added. The quantity required for its saturation was two drachms eighteen grains. The precipitate exactly resembled that afforded by the galls. And the decoction of logwood became of a sapphire blue color, by the addition of sulphate of iron: if the point of saturation be exceeded, the blue becomes greenish and dirty. The exact quantity required for saturation was found to be one drachm forty-eight grains, and the weight of the precipitate was two drachms twelve


grains. The different precipitations made by oak take place readily; that by logwood, a little more difficulty, but still more easily than that which is effected by galls.

64. It was most ascertained, by trials made with cloth, that the quantity of astringent substances required to give a black color of intensity, to an equal weight of the same cloth, was proportional to the quantities of astringent principle, which had been already estimated in each kind from the foregoing experiments; but the black obtained by the different parts of the oak does not resist proofs of color, nearly so well as that which is produced by galls. Logwood alone seems not capable of producing so intense a black as galls or oak; nor does the color which it produces stand the test of proofs so well as that produced by galls.

64. It was next ascertained, by trials made with cloth, that the quantity of astringent substances required to give a black color of intersity, to an equal weight of the same cloth, was proportional to the quantities of astringent principle, which had been already estimated in each kind from the foregoing experiments; but the black obtained by the different parts of the oak does not resist proofs of color, nearly so well as that which is produced by galls. Logwood alone seems not capable of producing so intense a black as galls or oak; nor does the color which it produces stand the test of proofs so well as that produced by galls.

65. We shall now consider the astringent principle in regard to its property of combining with vegetable and animal substances, particularly the latter. Silk acquires by galling, which is an operation that consists in macerating a stuff in decoction of some astringent substance, a weight which cannot be taken from it, or diminished beyond a certain degree, by repeated washing; after which operation the stuff when put into a solution of iron is dyed black, because the astringent principle, decomposing the sulphate of iron, forms a triple compound with the oxide of iron and the stuff which is dyed. A stuff that is galled is likewise capable of combining with other coloring particles, the colors of which thereby acquire fixity, if they do not naturally possess it; so that the astringent communicates its durability to the triple compound, or perhaps the more complex one which is formed; but by this union the color generally becomes of a deeper shade. The astringent principle, by combining with animal substances, renders them incapable of corruption, and tends to render their texture more compact; and in this the art of tanning consists.

66. It may be proper to take some notice here of the substance denominated tannin, which, while it has some properties in common with the gallic acid, differs from it in others. Seguin was the first who showed that astringents contained a peculiar substance, which, in combining with skin, gave it the properties of tanned leather, and that the tanning effect arose from the combination thus formed. Tannin may be produced by digesting gall-nuts, grape-seeds, oak-bark, or catechu, in a small quantity of cold water. The solution, when evaporated, affords a substance of a brownish-yellow color, highly astringent, and soluble in water and in alcohol. According to Mr. Brand, the purest form of tannin appears to be derived from bruised grape-seeds; but even here, he observes, it is combined with other substances, from which it is, perhaps, scarcely separable. I have never, says he, been able to obtain it of greater purity than by digesting powdered catechu in water at 33° or 34°, filtering again, and ecaporated to deyness; cold water, applied as before, extracts nearly pure tannin. The most distinctive character of tanning is that of affording an [...] precipitate when added to a solution of [...] or any other animal jelly. On this property [...] art of tanning depends, for which the bark is generally employed; but the bark [...] other trees are frequently employed for [...] purpose. Professor Prous [...] precipitation of a decoction of galls [...] carbonate of potassa, for obtaining [...]ing well the greenish-gray flates that [...] with colf water, and drying them in a [...]. This precipitate becomes brown in [...] brittle and shining like a resin, and [...] soluble in hot water. In this state [...] he says, is very pure. According to [...] tannin consists of hydrogen 4135 + [...] 51 160 + oxygen 44 645.

67. M. Berthollet consider the [...] charcoal as theessential characteri[...] astringent principle; the hydrogen, [...] contains only in small quantity, is [...] much dispposed partially to combine [...]. Hence, when an infusion of galls in [...]tacy with vital air, a small quantity of [...] is absorbed, and yet the color of [...] becomes much deeper; for in [...] the heory already laid down, the [...] readily becomes predominant in [...] the slight combustion, and the color is [...] deeper, and becomes brown.

68. Substances which contain much [...] and can undergo only a slight degree of [...], ought to possess a considerable [...] because charcoal does not combine [...] in the ordinary temperature of the air, [...] union be assisted by other attract[...] because slight variations of temperature [...] no change in the dimensions of charcoal [...] on the contrary, substances which contain [...] hydrogen, and in which the particles [...] hydrogen are in a state of division, [...] easily decomposedn by the combin[...] hydrogen with atote or oxygen. The [...] of their parts ought to take place [...] variations of temperature, because [...] dilatable by heat, which hte carbo[...] are not. When, therefore, the [...] principle is combined with an animal [...] it communicates to it the properties [...] derives from the charcoal; the animal [...] becomes less liable to change from [...]tions of temperature; instead of [...] it suffers a slight fegree of [...] action of the air; for the process of [...] propably could not go on in a [...] vessel.

69. On examining the analyses that [...] made of indigo, which mat be [...] the coloring matter least [...] with which we are acquainted [...] that this substance leaves, in [...] greater proportion of charcoal [...] themselves. M- Berthollet [...] also to this abundance of [...] durability of the color of indigo [...] and that the proportion [...] the chief cause of the difference [...] durability of colors; but the [...] may also have great influence, [...]


which combines intimately with another substance, ought to form with it a more permanent compound, than one which has only a slight composition to unite with it; now the astringent principle possesses a very strong disposition to frorm intimate combinations, especially with animal substances.

70. Upon the same principles may be ex[]ained the fixity communicated to coloring particles by alumine, and by those metallic oxides which are not liable to contain different proportions of oxygen, such as the oxide of tin, and some others. The different coloring substances, capable of uniting with metallic oxides, [...] an action upon them, analogous to that of astringents. The oxides are deprived of more or less of their oxygen, according to the force with which they retain it, the strength of attraction with which the coloring particles tend to combine with them, the proportions in which they meet with each other, and the greater or less disposition of the coloring particles towards combustion.

71. The coloring particles also suffer a change in their constitutuion from these circumstances: [...] the solutions of iron render brown all the colors into which oxide of iron can enter, although it has only a green or yellow color in the state in which it is held in solution by acids, and this effect goes on increasing to a certain degree; but the alteration of the coloring particled may afterwards be carried so far as to spoil their color, and to diminish their tendency to combination; the oxide of iron is then brought back to the yellow color by the oxygen which it attracts, and is capable of retaining. The action of metallic oxides and the coloring particles on each other, explains the changes observed in solutions of the coloring particles, when mixed with metallic solutions. The effect is gradual, as has been shown with respect to fustic. It sometimes happens that the mixture does not even grow turbid immediately, but loses its transparency by degrees; the precipitation begins; the sediment is formed; and its color becomes gradually deeper. In producing these effects, light has sometimes a considerable share.

72. Upon the whole, we may conclude, that metallic colors should be distinguished from those which are peculiar to substances of the vegetable and animal kind: that the color of metals are modified and changed by oxidation, and by the proportion of axygen with which they are combined; and that vegetable and animal substances may themselves possess a peculiar color, which varies in the different states through which they pass, or they may owe their colors to colored particles, either combined, or simply mixed with them. These are the particles which are extracted from different substances, and which undergo different preparations, in order to render them proper for the various purposes of dying. And the coloring particles possess chemical properties which distinguish them from all other substances: the affinities which they have for acids, alkalis, earths, metallic oxides, oxygen, wool, silk, cotton, and linen, from the principal of these properties. In proportion to the affinity which the coloring particles have for wool, silk, cotton, and linen, they unite more or less readily and intimately with them: and thence arises the first cause of variation in the processes employed, according to the nature of the stuff, and of the coloring substance employed. Nad by the affinity which the coloring particles have for alumine and metallic oxides, they form compounds with these substances, in which their color is more or less modified, and becomes more fixed, and less affected by external agents than before. This compound being formed of principles which have separately the power of uniting with vegetable substances, and more especially with animal substances, preserves this property, and forms a triple compound with the stuff; and the color, which has been again modified by the formation of this triple union, acquires a greater degree of fixity, and of indestructibility, when exposed to the action of external agents.

73. The coloring particles have often so great an affinity for alumine and metallic oxides, that they separate them from acids which held them in solution, and fall down with them; but the affinity of the stuff is sometimes necessary, in order that this separation may take place. The oxides of metals, which combine with the coloring particles, modify their colors, not only by their own, but also by acting upon their composition by their oxygen. The change which the coloring particles thereby suffer, is similar to that occasioned by the air, which injures every color in a greater or less degree. In the two different principles which constitute the air or the atmosphere, it is only the oxygenous gas that acts upon the coloring particles. It combines with them, weakening their color, and rendering it paler; but presently its action is principally exerted on the hydrogen, which enters into their composition, and it then forms water. This effect, continues M. Berthollet, ought to be considered as a true combustion, whereby the charcoal which enters into the composition of the coloring particles becomes predominant, and the color commonly changes to yellow, fawn color, or brown; or the injured part, by uniting with what remains of the original color, causes other appearances of a different kind. The combustion of the coloring particles is increased by light, and frequently cannot take place without its aid; it is indeed in this way that it contributes to the destruction of colors. Heat promotes it also, but less powerfully than light, provided its intensity be not very great. The effects of the nitric acid, the oxygenated muriatic acid, and even the sulphuric acid, when they make the color of the substances upon which they act pass to a yellow and even to black, are to be attributed to a combustion of a similar nature.

74. The effects of combustion may, however, be concealed, by the oxygen combining with the coloring particles, without the hydrogen being particularly acted upon by it. But colors are more or less fixed, in proportion to the greater or less disposition of the coloring particles to suffer this combustion. There are some substances also capable of acting on the color of stuffs, by a stronger affinity, or by a solvent power; and in this consists the action of acids, alkalis, and soap.


A small quantity of these agents, however, may sometimes form supercompounds with the stuff, and its color may be altered in that way. The oxides of metals produce in the coloring particles, with which they unite, a degree of combustion proportioned to the quantity of oxygen which these particles can take from them. Therefore the colors, which the compounds of metallic oxides and coloring particles assume, are the product of the color peculiar to the coloring particles, and of that peculiar to the metallic oxide: but the coloring particles and metallic oxides must be considered in that state to which they have been reduced by the diminution of oxygen in the particles that produce the color. It follows from this, that the metallic oxides, to which the oxygen is only slightly attached, are not fit to serve as intermedia for the coloring particles, because they produce in them too great a degree of combustion; instances of this kind are the oxides of silver, gold, and mercury. The oxides which undergo considerable alterations of color, by givibg off more or less of their oxygen, are also bad intermedia, particularly for light shades, because they produce changeable colors; examples of this kind are the oxides of copper, of lead, and of bismuth. The oxides which strongly retain their oxygen, and undergo very little change of color by the loss of a proportion of it, are the most suitable for this purpose; such is particularly the oxide of tin, which quits its menstruum easily, which has a strong affinity for the coloring particles, and which affords them a basis that is very white, and proper for giving a brightness to their shades, without altering them by the mixture of another color. The oxide of zinc is possessed of some of these properties in a considerable degree.

75. To account for the colors, which proceed from the union of the coloring particles with the basis which a mordant gives them, we must attend to the proportion in which the coloring particles unite to that basis. Thus the solution of tin, which produces a very copious precipitate with a solution of coloring particles, and which thereby proves that the oxide of tin enters in a large proportion into the precipitate, has much greater influence on the color of the precipitate, by the whiteness of its basis, than the solution of zinc, or that of alum, which generally produce much less copious precipitates. The precipitates produced by these two last substances retain very nearly the natural tint which the coloring particles afforded. It is therefore necessary to distinguish, in the action of mordants, the combinations that may take place by their means, between the coloring particles, the stuff, and the intermedium; the proportions of the coloring substances and intermedium; the modifications of color, which may arise from the mixture of the color of the coloring particles, and of that of the basis to which they are united; and the changes which the coloring particles may suffer, from the combustion that may be produced by the substance that is employed as an intermedium. It is evident also, that astringents do not differ essentially from coloring particles; but the latter take this name, especially when employed to produce black with oxide or inron, by [...] this metal to the state of black oxide [...] by their assuming a dark color from [...] oxygen.

76. The notion of an astringed [...] moreover, the property of combining [...] quantity with animal substances, [...] thus solidity and incorruptibility; because two properties are most commonly united. [...] again are derived from their large shared [...]bon, a circumstance in their composition gives them increased tendency to [...] greater stability.

77. On this ingenious theory of Berthollet [...] Bancroft, an able writer on dyeing, [...] some remarks that deserve attention. [...] opinion M. Berthollet, in ascribing the [...] of vegetable and animal coloring [...] general, to effects or changes similar to [...] combustion, has gone much farther than [...]rantable by facts. It cannot, he thinks [...] intention, that we should apply the [...] combustion to alterations which result from simple addition of oxygen to coloring [...]with a destruction or separation of any [...] component parts; though many of the [...] and extinctions of these colors evidently [...] only from such simple additions of oxygen [...] nitric, sulphuric, and other acids, [...] oxygen, have the power nor only of [...] but of extinguishing, for a time, the [...] many tingent matters; not by any [...] can properly be denominated a combustion rather by a change in their several [...] particular rays of light; but one of [...] being destroyed, or carried away, the [...] an alkaki, or of calcareous carbonate [...]nerally undo such alteration, and [...] original color, by decomposing and [...] the acid or oxygen which had caused the [...]tion.

78. Of this numerous instances might [...] it being the case of almost all vegetable and animal coloring mattters. It will be [...]mention, that ink dropped into a glass of [...] nitric, vitriolic, or other acid, will lose [...] and that it may be again restored by [...] suitable portion of vegetable or fossil [...] that this may be done several times [...] ink, and therefore the change or loss of [...] could not have been the effect of com[...]. If, however, this ink had not been fixed by [...]ing in the substance either of wool, silk, [...] or cotton, and the substance so dyed had [...] dipped into a glass of diluted acid, a [...]able part of the coloring matter would [...] dislodged, and separated from the dyed substance, by its affinity with the oxygen or [...] although no combustion had taken place [...] color so separated and lost could not be [...] restored without second dyeing. The [...] color would be similar to what [...]pens to colors from exposure to the [...] by which they are gradually weakened, [...] them without any other change of [...] simple diminution of their [...] coloring matter; and this [...] fugitive colors, particularly that of [...] cloth is soon left as white as before it [...]


[...]ad, without any thing like combustion having [...] taken place in it, or in the matter with which it was dyed. It may also be presumed, that colors are not generally inpaired by any thing like combustion, from this fact, that there are but few of them which the common muriatic acid does not injure, as much as either the nitric or the sulphuric; and as there can be no comnustion without oxygen, and as the common muriatic acid either contains none, or what it does contain [...] confessedly combined with it by an affinity too powerful to be overcome by any known substance it means, it follows, that the oxygen (if it contain any) cannot be liberated so as to act in the way of combustion upon any other matter; and therefore, when the common muriatic acid changes or destroys the colors, it changes or destroys the affinities upon which they depend, by producing effects different from those of combustion; and [...] the changes which it produces on colors are [...] most cases similar to those produced by the nitric, sulphuric, and other acids known to contain oxygen, it is reasonable to conclude, that these also act upon colors, by producing other effects than those of combustion.

79. M. Sennebier exposed a great variety of woods to the action of the sun and air, and found all their colors very soon affected. The white woods generally become brown, and the red and violet changed either to yellow or black. Guaincum was rendered green; the oak and the cedar were whitened, as were the brown woods generally; effects which certainly do not resemble those of combustion, any more than the bleaching of wax or tallow by exposure to the air. It is therefore evident, argues Fr. Bancroft, that the color of each particular substance depends on its constitution, producing in it a particular attraction for certain rays of light; and a disposition for certain rays of light; and a disposition to reflect or transmit certain other rays; and in this respect it may doubtless suffer very considerable changes from the action or combination of oxygen, without any effects similar to those of combustion. And, indeed, the changes of color which arise from the access of atmospheric air, seldom resemble those which the mere predominance of blackness (the supposed natural color of carbon) would produce; though this may have been the case with the coloring matter of brown or unbleached linen, upon which the experiments of M. Berthollet seem principally to have been made. But whether the action of vital air, or its basis, in promoting the decays and colors, ought to be denominated a combustion or sot, Dr. Bancroft is confident, that at least some of them are liable to be impaired, not so much by the accession of oxygen, as by the loss of it. The difference of color in arterial and venous blood had been long noticed, and numerous experiments have shown that the fine vermilion color of the former is produced solely by vital air, which it is capable of acquiring through bladders, the costs of blood-vessels, &c. And Mr. Hassenfratz seems to have proved, that, as this fine red color is gained by a dissolution of oxygen in the arterial blood, so it is lost, and the dark color of the venous blood restored, by a separation of the oxygen, in consequence of its forming a new combination with the hydrogen and carbon of the same.

80. Dr. Bancroft is also of opinion, that the blue color of indigo depends upon a certain portion of oxygen, for he has found that solution of indigo, by losing its oxygen, may become as pellucid, and, expecting a very slight yellowish tinge, as colorless as water, and afterwards speedily rreturn through all the shades of yellow and green to its original deep blue, by exposure to atmospheric or vital air. Similar to this, he remarks, is the fact long since observed by the abbè Nollet, of the tincture of archil employed to color the spirit of wine used in thermometers, and which after some time loses its color, but recovers it again upon being exposed to atmospheric air. This also happens to the infusion of turnsole, and to syrup of violets, which lose their colors when secluded from air, and regain them when placed in contact with it. He has also observed various animal and vegetable colors, produced solely by the contact of atmospheric air; and some others, which, when given by dyeing or callico-printing to wool, silk, cotton, &c., though unable to sustain a single day's exposure to the sun and air without manifest injury, were found to receive none from the action of strong nitric or sulphuric acuds, but, on the contraty, were perceived by being wetted with them, and even with oxygenated muriatic and sulphuric acids. But the same colors, if covered with linseed oil, were found to decay more quickly from exposure to the sun and air, than if uncovered. These colors, therefore, he contends, could not owe their decay to the contact or combination of oxygen, because they were not only unhurt, but benefited by its concentrated powers in the nitric, the oxygenated muriatic, and sulphuric acids; and also because they were soonest impaired when defended from the access of oxygen, by being covered with linseed oil. Propably the decays of these colors were occasioned by a loss of at least some part of the oxygen which was necessary to their existence, and which the linseed oil assisted in depriving them of, by the strong affinity it has with oxygen.

81. Dr. Bancroft fursther observes, that, in forming systems, we are apt to draw general conclusions from only a partial view of facts. This M. Berthollet seems to have done, not only in ascribing the decays of vegetable and animal colors, exclusively to effects similar to those of combustion, but also in representing the oxygenated muriatic acid, as an accurate test for anticipating, in a few minutes, the changes which these colors are liable to suffer by long exposure to the action of sun and air; for, says he, though it is true, that the oxygenated muriatic acid, in weakening or destroying colors, gives up to them more or less of the oxygen which it had received by distillation from manganese; and that, by this new combination of oxygen those affinities for particular rays of light, upon which their colors depend, are liable to be destroyed; it is nevertheless true, that the changes of color so produced are no certain indication of those, which the combined influence of light and air will occasion upon colors in general; there being several colors which are very speedily destroyed by the latter of the causes, though they resist the strongest action of the oxygenated muriatic acid, without suffering any degree of


injury or hurt. The Fr. adds, that M. Berthollet well knows, since nobody has contributed more to ascertain, how much the properties of oxygen are diversified by each particular basis to which it unites; and that it does not, therefore, seem warrantable to imagine, that its action will not be modified by a basis so powerful as that of the common muriatic acid, or that the united properties of both should represent or resemble those of atmospheric air upon colors, any more than they do in the lungs by respiration; where, instead of supporting life, they would instantly put an end to it.

82. These observations were made in reference to the matter in which M. Berthollet had expressed himself on the subject in his Elements de l'Art de la Teinture, published in 1791. A new edition of this work was published about the year 1804, in which the author has fully noticed Dr. Bancroft's arguments; refused some of them; admitted the force of others in part; and in some respects, has availed himself of the important imprevements of Fr. Bancroft.

Of The Differences Between Animal And Vegetable Substances.

83. Before we proceed to treat of the practise of dyeing, it will be necessary to consider some of the leading differences that exist between several of the substances to be dyed, and to point out the processes through which they must pass before they will receive the colors required. The following is the substance of M. Berthollet's opinion relative to this subject: - It is now known that the composition of animal substances is distinguished from that of vegetables, by their abounding in a particular principle called azote, which is found only in small quantities in vegetables, as well as by their containing much more hydrogen, or base of inflammable air, than is found in the other. From these two causes, the differences observed in the distillation of animal and vegetable substances proceed: the former yield a large quantity of ammoniac or volatile alkali; the latter afford very little, and sometimes yield an acid: the former yield a great deal of oil, the predominant principle in which is hydrogen, which is very volatile and disposed to fly off by a small increase of temperature; while the latter sometimes do not yield it in the least sensible quantity.

84. Dr. Ure in a note, p. 151, vol I. of his translation of Berthollet's treatise, has the following remarks on this theory. Modern researches fo not justify this position of M. Berthollet. Sugar and stach, by the analyses of M. M. Gay Lussac and Berselius, contain about as much hydrogen as fibrin does, and very little less gelatin and albumen; while, by my analyses, wool and silk contain less hydrogen than cotton and flax. See Phil. Trans. for 1822.
I subjoin the results of my analytical experiments on the four principal subjects of dyeing,
Carbon | Hydrogen | Oxygen | Amots.
Wool 53-70 | 2-80 |31-90 |12-30
Silk 50-69 |3-94 |34-04 | 11-33
Cotton 42-11 | 5-06 | 52-83
Flax 42-81 | 5-30 | 51-70
The first two, independently of the [...]sess a marked difference of composition [...] their excess of carbon and deficiency of [...].

85. In consequence of this [...] animal substances, when set on for [...] bright flame, which breaks out at the [...] but is soon stifled by the charcoal [...] formed, and which has peculiar properties, the combustion is accompanied with a [...] odor, owing to the ammoniac and [...] escape unconsumed; they are liable to [...]faction, in which process ammoniac is [...] as well as in their distallation, by a [...] union of the acote and hydrogen; [...] table substances, on the contrary [...]vinious and acetous fermentation. It is [...] that, as animal substances contain a considerable quantity f principles disposed to [...] elastic form, they have less cohesive form [...] their particles than vegetables, and a [...] position to combine with other substances; [...] they are more liable to be destroyed by [...] agents, and are more disposed to combine with coloring particles.

86. The consequence of this action on [...] substances is, that they cannot [...], and that alkalis should be used with great [...] the processes employed for dyeing them; [...]as no danger is to be apprehended from [...] of alkalis with substances of vegetable kind. Nitric and sulphuric acids have also a [...]derable action on animal substances: the [...] decomposes them, extricates the azote, [...] the fatty matter, and forms acarbonic acid [...] fixed air, and oxalic acid or the acid [...] with a part of the hydrogen and a part of the charcoal; the latter extricates the inflammable gas, probably azotic gas, and reduces the [...] principles to the state of carbon. [...] some resemblance to vegetable substance, [...] its being less disposed to combine with [...] particles, and by resisting the action of [...] and acids more powerfully; which may [...] either from the same principles being [...]mately combinet in it than in wool, or, more propably, from its containing less [...] and hydrogen. But, though the action of [...] and acids upon silk be weaker than upon wool, [...] should still be employed with great caution, because the brightness of color required [...] appears to depend upon the smoothness of a surface, which should, on that account, be preserved unimpaired, with every possible [...]. Cotton withstands the action of acids much better than flax or hemp. Even the nitric acid [...] not destroy it without great difficulty.

Of Wool

87. The value of wool, and its [...] for [...] differennt kinds of manufacture, depend upon the lenght and fineness of its filaments. [...] naturally covered with a kind of grease, which preserves it from moths; so that is [...] until ot is about to be dyed, or formed [...]. To scour wool, it is generally pet for short [...] quarter of an hour into a kettle, [...] sufficient quantity of water, mized with [...]fourth of putrid urine, heated to such [...] as the hand can just bear, and it must be [...] from time to time with sticks. It is then taken


out, put to drain, and carried in a large basket [...] running water, where it is moved about until the grease is entirely separated, and no [...] renders the water turbid; it is afterwards taken out, and left to drain. It sometimes loses in this operation more than a fifth of its weight. This operation should be conducted with much care, since the more correctrly it is performed, the better is the wool fitted to receive the dye. [...] this process the ammonia or volatile alkali which exists in the urine, readily combines with the oil of the wool, and forms a soap, which, [...] soluble in water, is dissolved and carried [...].

88. Wool is dyed in the fleece before it is spun, when it is intended to form cloths of mixed colors; it is dyed after being spun, when intended principally for tapestry: but it is most generally dyed after having been manufactured [...] cloth. If wool be dyed in the fleece, its [...] from being separate, absorb a larger quantity of the coloring particles than when it is spun; for the same reason, woollen yarn takes up more than cloth: but cloths themselves vary considerably in this respect, according to their degree of fineness, or the closeness of their texture. Besides, the variety in their dimensions, the different qualities of the ingerdients employed in dyeing, and a difference of circumstances in the process, prevent us from relying upon the precise quantities recommended for the processes. This ought in all dyes to be attended to. It is a fact well known to dyers and others, that the coarse wool from the thighs and tails of [...] sheep receives the coloring particles with great difficulty. The finest cloth is never fully penetrated with the scarlet dye, hence the interior of the cloth appears always of a lighter shade when cut, and sometimes almost white. For the generality of colors, wool requires to be prepared by a bath, in which it is boiled with saline substances, principally with alum and tartar: but there are some dyes for which the wool does not require such a preparation; then it must be well washed in warm water, and wrung out, or left to drain.

89. The surface of the filaments of wool or hair is not quite smooth; for, although no roughness or mequality can be discovered, yet they seem to be formed of fine laminae placed over each other in a slanting direction, from the root of the filaments towards the point, resembling the amagement of the scales of a fish, which cover each other from the head of the animal to its tail. This peculiarity of structure is proved by a simple experiment. If a hair be held by the root in one hand, and drawn between the fingers of the other hand, from the root towards the point, hardly any friction is perceived, and no noise is heard; but if it be seized by the point, and passed in the same manner between the fingers from the point towards the root, a resistance is felt, and a tremulous motion is perceptible to the touch, while the ear perceives a slight noise. Thus it appears, that the texture is not the same from the root towards the point, as it is from the point towards the root. This is further confirmed by another expirement. If a hair be held between the thumb and fore-finger, and they be rubbed against each other in the longitudinal direction of the hair, it acquires a progressive motion towards the root. This effect depends not on the nature of the skin of the finger, or on its texture, for if the hair be turned and the point placed where the root formerly was, the motion is reversed, that is, it will still be towards the root.

90. On this peculiarity of structure, which was oberved by M. Monge, depend the processes of felting and fulling of hair and wool for different purposes. In the process of felting, the flocculi of wool are struck with the string of the bow, by which the filaments are detached, and dispersed in the air. These filaments fall back on each other in all directions, and, when a layer of a certain thickness is formed, they are covered with a ckith, on which the workman presses with his hands in all parts. By this pressure the filaments are brought nearer to each other; the points of contact are multiplied, the progressive motion towards the root is produced by the agitation; the filaments entangle each other; and the laminae of each taking hold of those of the others, which are in an opposite direction, the whole is retained in a state of close contexture.

91. Connected with this operation is that of fulling. The roughness on the surface of the filements of wool, and their tendency to acquire a progressive motion towards the root, produce great inconvenience in the operations of spinning and weaving. This inconvenience is obviated by covering the filaments with a coat of oil, which fills up the pores, and renders the asperities less sensible. When these operations are finished, the stuff must be freed from the oil, which would prevent it from taking the color with which it is to be dyed. For this purpose it is taken to the fulling-naill, where it is beaten with large beetles, in a through of water, through which clay has been diffused. The clay unites with the oil, which, being thus rendered soluble in water, is carried off by fresh portions of water, conveyed to it. In this way the stuff is scoured; but this is not the sole object of the operation. By the alternate pressure of the beetles, an effect similar to that of the hands of the workman, in the operation of felting, is produced. The filaments composing a thread of warp or woof, acquire a progressive motion; are entangled with the filaments of the adjoining threads; those of the latter into the next, and so on, till the whole become felted together. The stuff is now contracted in all its dimensions, and, participating both of the nature of cloth and of felt, may be cut without being subjected to ravel; and, when employed to make a garment, requires no hemming. In a common woollen stocking web, after this operation, the stitches are no longer subject to run, and, the threads of the warp and woof being less distinct from each other, the whole stuff is thickened, and forms a warmer covering.

Of Silk.

92. Silk in its natural state is coated over with a substance which has generally been considered as a kind of gum or varnish. To this


substance the silk is supposed to owe its elasticity and stiffness. Besides this varnish, the silk usually met with in Europe is impregnated with a substance of a yellow color, and, for most of the purposes for which silk is required, it is necessary to free it from both the varnish and the coloring matter. To effect this, the silk is subjected to the operation of scouring; but it is very obvious that when the silk is to be dyed, the scouring need not be carried so far as is required where it is to remain white. Different colors, also, will require different degrees of scouring; and this difference is generally regulated by the quantity of soap employed: 100 pounds of silk boiled in a solution of twenty pounds of soap, for three or four hours, supplying a little water occasionally because the ecaporation, will be sufficiently prepared to receive the common colors. For blue colors the proportion of soap must be greater; and scarlet, cherry color, &c., require a still gerater proportion, because for those color the groundm ust be whiter.

93. When silk is to be employed white, it must undergo three operations. The first consists in keeping the hanks of silk in a solution of thirty pounds of soap to 100 of silk: this solution ought to be very hot, but not boiling; when any part of the hanks immersed is entirely free from its gum, which is known by the whiteness it acquires, the hanks are to be shaken over, as the dyers term it, so that the part which wasn ot before immersed, may undergo the same process. They are then taken out and wrung, as the process is finished.

94. In the second operation the silk is put into bags of coarse cloth, each bag containing from twenty-five to thirty pounds. A solution of soap is prepared as in the former case, but with a smaller proportion of soap. In this the bags are boiled for an hour and a half; and that they may not receive too much heat by resting on the bottom of the vessel, they must be constantly stirred during the operation.

95. The third operation is to communicate to the silk different shades, that the white may be rendered more pleasing. These shades are known by different names, as China-white, silver-white, azure-white, or thread-white. For this purpose a solution of soap is also prepared, of which the proper degree of strenght is ascertained by its manner of frothing by agitation. For China-white, which is required to have a slight tinge of red, a small quantity of anatto is added, and the silk is shaken over in it till it has acquired the shade required. IN other whites, a blue tinge is given by adding a little blue to the solution of soap. The azure-white is produced by means of indigo. To prepare the azure, fine indigo is well washed in morerately warm water, after which boiling water is poured upon it. It is then left to settle, and the liquid part only, which contains the finer and more soluble parts, is employed.

96. Some use no soap in the third operation, but, when the second is completed, they wash the silks, fumigate with sulphur, and azure them with river water, which should be very pure. But all these operations are not sufficient to give silk that degree of brightness which is [...] when it is to be employed in the [...] white stuffs. For this purpose it must [...] the process of sulphuration, in which [...]exposed to the vapor of sulphur. [...] the silk which has been thus treated in [...]ceiving colors, and retaining them is [...]lustre, the sulphur which adheres to a [...] separated by immersion and agitation [...] time in warm water, otherwise to [...] tarnished and greatly injured.

97. It has long been an object of [...]able importance, to deprice silk of its [...] matter, without destroying the [...] its stiffness and elasticity depend. A [...] for this purpose was discovered by Beau[...] as it was not made public, others have [...] to it by conjencture and experiment. [...]ing account, given by Berthollet, is all [...] transpired concerning this process. A [...] is made with a small quantity of [...] and alcohol. The muriatic acid should [...] state of purity, and entirely free from [...] acid, which would give the silk a yellow [...]. In the mixture thus prepared, the silk [...] immersed.

98. One of the most difficult parts of processm especially when large quantities are operated upon, is to produce a uniform [...]ness. In dyeing the whitened silk, there is [...] some difficulty in preventing its curbs; [...] it is recommended to keep it constantly [...] during the drying. The muriatic acid [...] be useful in this process, by softening the [...] and assisting the alcohol to dissolve the coloring particles which are combined with it. The alcohol which has been impregnated with coloring matter may be gain separated [...] and purified, and may thus serve in [...]rations, and render the process more [...]. This may be effected by distillation [...]derate heat, in glass or stone-ware vessels.
The preparation with alum is very [...] preliminary operation in the dyeing [...]. Without this process, few colors [...] either beauty or durability. Forty or [...] of alum, dissolved in warm water, are [...] a vat, with forty or fifty pails of [...] prevent the crystallisation of the salt, the [...] must be carefully stirred during the [...]. The silk being previously washed and [...] to separate any remains of soap, is [...] this alum liquor, and after eight or nine [...] wrung our, and washed in a stream of water [...] pounds of silk may be prepared in the [...] quantity of liquor; but when it begans to [...] weak, which may be known by the [...] or twenty-five pounds of alum are to be added and the addition repeated till the liquor [...] an offensive smell. It may then be employed [...] the preparation of silk intended for darker [...] till its whole strength is dissipated. This preparation of silk with alum must be made [...] cold; for when the liquor is employed [...] lustre is impaired.

Of Cotton

99. Cotton is the down or wool obtained from the pods of the gossipium, a shrubby plant [...]


grows in warm climates. Cottons daffer principally in the lenght of their filaments, their [...], strenght, and color. This substance [...] different shades, from a deep yellow to a white. The most beautiful is not always the whitest; it is necessary to bleach it, by processes similar to those employed in the bleaching of linen. Or, instead of these, oxygenated muriatic acid may be employed; and a more beautiful white thus produced, than by the ordinary way of bleaching. M. Berthollet succeeded in bleaching the yellow cotton of St. Domingo which very obstinately retains this bad color. But, that cotton may be disposed to receive the dye, it must undergo scouring. Some boil it in our water, but more frequently alkaline lie used; the cotton must be boiled in it for two hours, and then wrung out; after which it must be rinsed in a stream of water, till the water [...] of clear; it must then be carefully dried. M. Berthollet has observed, that the acid which had been used in this operation, had taken up a quantity of calcareous earth and iron, which would have injured the colors very much. Aluming and galling are generally employed in the dyeing of cotton and linen. In the preparation with alum, about four ounces of it are required to each pound of stuff; it must be dissolved with the precautions abovementioned. Some add a solution of soda in the proportion of one-sizteenth of the alum; others a small quantity of tartar and arsenic. The thread is wel impregnated by working it pound by pound in this solution; it is the put altogether into a vessel, and what remains of the liquor is poured upon it. This is left for twenty-four hours, and then removed to a stream of water, where it remains for about two hours, to extract a part of the alum, and is then washed. Cotton, by this operation, gains about one-fortieth of its own weight.

100. In the operation of galling, it is usual to employ different quantities of galls or other astringents, according to their quality, or the effect to be produced. Powdered galls are boiled for about two hours, in a quantity of water prooirtioned to that of the thread to be galled; the liquor is then allowed to cool to a temperature which the hand can bear, after which it is divided into a number of equal parts, that the thread may be wrought pound by pound; and what remains is poured upon the whole together. It is then left for twenty-four hours, when intended for black, but for other colors twelve or fourteen hours are sufficient. It may then be wrung our, and carefully dried. When stuffs are galled, which have already received a color, the operation is to be performed in the cold, that the color may suffer no injury. M. Berthollet found that cotton which had been alumed, acquired more weight in the galling than that which had not undergone that process; although alum adheres but in a small quantity to cotton, it communicates to it a greater power of combining, both with the astringent principle and with the colouring particles of different substances.

Of Flax.

101. Flax must undergo several preparations before it be fit to receive the dye. Of these, the watering is an operation of much consequence, from its influence on the quality and quantity of the product, and from its deleterious effects on the air. In this operation, a glutinous juice, which holds the green coloring part of the plant in solution, undergoes a greater or less degree of decomposition, according to the mode of conducting the operation. This matter seems to resemble the glutinous part, that is held dissolved in the juice procured from green plants by pressure, which is separated along with the coloring particles by a heat approaching to that of ebullition, which becomes putrid, and which affords ammonia by distallation; but it is probable, that water alone cannot sufficiently separate it from the cortial parts: whence the hemp, which has been watered in too strong a current, is deficient in its softness and pliability, &cr. But if the water employed be stagnant and putrid, the hemp acquires a brown color, loses its firmness, and emits highly noxious vapors. This process is therefore performed to the greatest advantage, in watering pits situated on the banks of rivers, where the water may be changed often enough to prevent a putrefaction, that would injure the hemp, and be prejudicial to the workmen; yet not so often as to hinder the degree of putrefaction which is necessary to render the water capable of dissolcing the glutinous substance. To prepare flax for the dye, it must also be subjected to the operations of scouring, aluming, and galling, in the same manner as cotton.

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