Chapter XX. On the Cultivation of Woad, and the Extraction of Indigo from it.
Chymistry applied to Agriculture.
By John Antony Chaptal, court of Chanteloup, Peer of France, Member of the Institute, &c.
Translated from the Second French Edition.
Boston: Hilliard, Gray, and co.
1836
ARTICLE III.
The Extraction of Indigo from Woad.
Before the discovery of indigo, the isatis tinctoria was cultivated for the manufacture of woad cakes in nearly all parts of Europe: the blue color obtained from this plant was the most durable one known, and the commerce in woad was immense.
The neighbourhood of Toulouse, and particularly Laraguaisi furnished an enormous quantity of woad, and the cakes prepared there were everywhere considered of the best quality this section of the country became so rich, that it was called the pays de cocagne, from the name of its manufacture; and this epithet has passed into a proverb, and is used to designate a very rich and fertile country.
Two hundred thousand packages of cakes were exported every year by the port of Bordeaux alone: so great was the want of this commodity amongst foreign nations, that, during the wars we were obliged to sustain, it was always agreed that the commerce in it should be free and protected, and that foreign unarmed vessels should be allowed to come into our ports to obtain it.
The finest establishments at Toulouse have been founded by the manufacturers of woad cakes; when Charles V. wished to secure the ransom of Francis I., who was a prisoner in Spain, he required that the rich Beruni, a manufacturer of this article, should become surety for it.
* This calculation is founded upon the supposition that 100 lbs. of woad leaves yield 3 oz. of indigo; for the cakes, which contain all the indigo of The plant, represent only ½ of the weight of leaves employed in their manufacture.The indigo, which is an extract from a plant of the same name, first made its appearance in Europe early in the seventeenth century; and the injury which the cultivation of woad would receive from it, was foreseen from the first moment of its introduction. An equal weight of the pure coloring principle of indigo contains about 165 times more coloring matter than the woad cakes do. Thus 15 lbs. of good indigo, such as is usually employed in dying, are equal, in point of coloring matter, to 2625 lbs. of the woad cakes. From this some judgment may be formed of the difficulty of producing a deep dye with the woad alone; for, besides the inconvenience of managing such an enormous mass of matter in a dye, the colorer must be very skilful in his art to draw from it a uniform and wellsustained color. It is not then astonishing, that the use of indigo should have superseded that of the cakes, and that consequently the culture of woad should be much diminished.
Henry IV., who foresaw the depreciation of this principal branch of French agriculture, wished to arrest the evil in its infancy, and by an edict of 1609, he pronounced the penalty of death against all those who should make use of "the false and pernicious drug called indigo." The same severity was adopted by the governments of Holland, Germany, and England, though they had not the same interest in the subject: the law was, however, maintained and executed only in the last of these kingdoms.
This source of prosperity may easily be revived in France, not however by increasing the manufacture of woad cakes, of which we cannot extend the use, but by extracting from the leaves of the woad, indigo which shall be equal to that brought from India.
The long war of the revolution deprived us of navigation, and our colonial supplies of various articles became consequently very dear and incomplete: in this state of dietress and privation, government made an appeal to our learned men, upon the subject of attempting to obtain from our own soil a portion of the supplies, which had before been brought hither from the New World. The efforts made were not unsuccessful, and in a short time indigo was made from woad, which was not excelled by the best of that brought from Guatimala.
Three large establishments for the manufacture of this article, were established at the expense of government; one at Albi, another in the neighbourhood of Turin, and a third in Tuscany. These establishments prospered for several years, and the processes for obtaining indigo were much improved in them; but the changes which took place in 1813, deprived the manufactories of protection; the establishments were sold by the respective governments, and thusthis profitable branch of industry, which would have continued if the establishments had belonged to individuals, has disappeared. M. Rogues, a skilful, dyer at Albi, has alone maintained an establishment that he had formed, and during ten years he has made use of no other indigo for coloring than that which he prepared himself from woad.
At this time, nothing more is necessary than to make known those simple and advantageous, methods by which this branch of manufacturing industry may be conducted. I shall however observe, that it is more profitable to the proprietor to extract the indigo from woad, than to convert the leaves of the plant into cakes.
Hellot assures us that it had been proved in his time, that four pounds of good Guatimala indigo yielded as much coloring matter as a package of Albigense woad cakes weighing two hundred and ten pounds.
* These results appear to me exaggerated. I place dependence only on those of the experiments which have been made under my own inspection.At Quiers, in Piedmont, where the dyers are very skilful, it is calculated that three hundred pounds of the cakes afford as much coloring matter as six pounds of the best indigo.*
According to the experiments of M. Giobert, there is no doubt that it is more profitable to extract indigo from the woad leaves, than it is to convert them into cakes.
The indigo which is obtained in America from the anil, in Indostan from the nuricum, and in Europe from the isatis, does not differ sensibly in character: the care which is taken in the manufacturing of it, and the state of the plants, which many circumstances may cause to vary during vegetation, can alone produce some changes in its color, and cause its value in commerce to vary.
This difference in the quality and price of indigo, may arise in some degree from the different methods adopted for extracting it. In America it is made to ferment cold; in Java in the form of a decoction; and generally in India, since the discoveries of the learned Roxburgh, by infusion.
Prior to the year 1810, a great number of processes had been employed in France, Germany, Italy, and England, for obtaining indigo from the isatis, without any general method having been established. It was at this period that the French government, urged by the necessity of obtaining a coloring substance which the state of the country would not allow them to import but at a great expense, formed establishments for the extraction of indigo from woad, and offered encouragement to those who would undertake the business.
I shall not describe all the methods that were practised during the three years following 1810. I shall confine myself to pointing out that which is the simplest, least expensive, and most expeditious; and which the most constantly furnishes indigo of a uniform and good quality.
No other apparatus is required in this process, than a boiler for heating water, one tub for leaching, a second for a receiver, and a bucket in which the water charged with indigo is beaten to precipitate the fecula.
The manner of operating, as described by M. Giobert, author of the process, is as follows.
Begin by heating the water till it boils. In the mean time, place the leaves of woad (which have been cut according to the signs of their fitness pointed out in the process for making woad cakes) in the tub, taking care to arrange them so that they shall not be anywhere crowded, and that the distribution shall be equal throughout the whole inside of the tub. Cover the tub with a hurdle of osiers, or with a coarse net, and throw over it a coarse woollen cloth.
When the apparatus is thus arranged, pour boiling water over the leaves till every portion of them be moistened, and the water stand upon the top. Remove the woollen cloth and the net, and stir the leaves gently, that the water may be equally diffused through them, and may not descend to the bottom of the tub, where it will not act upon them.
Allow the leaves to rest during five or six minutes, and then draw off the liquid through the stop-cock of the tub, causing it to pass through a sieve into the receiver. If the color of the liquid be too light, not having the depth of wellcharged new white wine, the flow of it must be stopped, and that which has run out is to be again turned upon the leaves, and allowed to remain until it has acquired the appearance just mentioned.
As soon as the liquor is drawn'off, turn a fresh quantity of warm water over the leaves, and allow it to. act upon them for the space of fifteen minutes. During this second infusion, remove the water of the first leaching into the bucket called the beater, and cause that of the second leaching to flow into it, thus mixing the two.
As the leaves are not by these two leachings exhausted of all their indigo, cold water must now be turned upon them; and this may remain an hour or two. The liquor of this third leaching is kept by itself, to be treated with lime-water. After it has been drawn off, the leaves may be strongly pressed, to obtain from them all the juice which may serve to deepen dyes, made of the cakes, for obtaining light blues. M. Pariolati, dyer at Quiers, has found this an excellent article for giving a fine blue to silks. But it can be employed only when the dye-house is in the neighbourhood of the indigo manufactory.
The leaves may also be bruised after having had the two first waters passed through them, and be formed into cakes in the usual manner. These cakes will not be of the first quality, but they are useful as a fermentable substance, and produce in this way the same effect upon the woad dye which is prepared for coloring. This has been proved by experiments conducted upon a large scale, and these cakes are in demand at a price one third less than those made from leaves containing all the indigo.
The process which I have described for obtaining indigo by a hot infusion, is more simple than any other mode. But as the indigo is more or less formed or oxidated in the leaves, according to the period of their vegetation, it is not at all times equally soluble, and especially when it is (as in leaves that have passed their maturity) in the state of blackish blue. It is therefore necessary, when this process is to be followed, that the leaves should be gathered between the sixteenth and eighteenth day of their growth, and before their borders become shaded with blue, as, when that takes place, the indigo has arrived at a degree of oxidation which prevents it from being completely dissolved.
If the method of obtaining indigo by fermentation be less advantageous than the one I have already described, it is capable of being employed upon leaves which have arrived at a higher degree of maturity, and I shall therefore give a short description of it; and I feel the more inclined to do this, because in small manufactories this process is on some accounts preferable to the other.
When indigo is to be obtained by fermentation, a tub is about three fourths filled with woad leaves, pressed down so that they shall remain immersed in the water, which is thrown over them of the temperature of 15° or 16° Réaumur, (= 65° to 68° Fahr.) The heat of the manufactory should be at the same degree. Fermentation will in a short time be evident by the appearance of bubbles, which rise and break upon the surface. This should be terminated in eighteen hours. The period when it should be stopped, may be known by the color of the water being that of a yellow lime, and by the formation, upon the top, of thin, greenish, and iridescent pellicle: When in this state, the liquor is to be drawn off into the receiving tub, and changed from that into the beating-vessel.
In both methods, it is necessary to precipitate the indigo which is held in solution or in suspension in the water; and this operation, which is called beetling or beating, is needed to give to the indigo the blue color which belongs to it.
There are two methods of beating which are practised, one being applicable to the liquor obtained by infusion, and the other to that procured by fermentation. I shall here describe both of them.
As soon as the heat of the liquor, which has been passed through the leaves in the manner described in the first process, has fallen to between 120° and 111° Fahrenheit, beating is commenced. The instrument employed for this purpose is a broom, or a handful of willow twigs from which the bark has been peeled. With this the liquor is forcibly agitated, the quickness of the motion being gradually lessened as the infusion cools.
As soon as a white foam rises upon the top, beating is suspended, but is resumed again as soon as the foam subsides, and assumes a fine blue color. If the liquor is too hot, or has been too much beaten, the blue borders upon the violet; otherwise it is the color of the sky. Beating is continued at intervals, allowing the foam to exhibit its color. When by rest it appears only of a pale blue, the beating is continued without any interruption. When the foam remains white, or changes to a reddish color, the operation draws to a close.
By beating, the color of the water, which was that of white wine, becomes more and more brown. The beating is ended, when upon pouring the liquor into a glass vessel, it appears of a uniform brown. Should a tinge of bluish green be perceived near the sides of the glass, the beating must be continued. Upon the whole, it is better to beat it too much than too little. The time requisite for performing the operation upon the liquor drawn from three hundred pounds of leaves, is generally about an hour and a half.
When the liquor is at length left undisturbed, the indigo is deposited in grains at the bottom of the bucket. Eight or ten hours are sufficient for this purpose. The liquor is then to be drawn off and the indigo dried, in order that all the water which could cause it to ferment may be separated from it.
In this operation, no foreign substance by which the indigo can be adulterated is employed; and it is therefore obtained as pure as the best of the imported kind.
When the leaves of the isatis are operated upon with cold water by maceration, fermentation, or any other method, the indigo cannot possibly be separated by beating. The reason of this is, that the elevation of the temperature is not high enough to cause the combination of oxygen with the indigo, and thus to give it the color and other characteristics which render it so valuable in the art of dyeing.
The substance which in these cases is most usually employed to produce precipitation, is lime-water; but as this process requires much attention, I shall describe particularly the use and action of this ingredient, that the manufacturer may be the better able to direct it.
After all the water which has been prepared in the course of the day, has been collected in a tub, the operation of precipitating the indigo from it is commenced in the following manner.
The liquor is beaten almost uninterruptedly, and without any particular method, for half an hour, the operation being interrupted only to allow the foam to subside and exhibit its color. When the liquor begins to appear of a deep brown, five or six pints of lime-water are thrown into it. The beating is continued, and the lime-water added at intervals, till the liquor exhibits a greenish yellow, begins to grow turbid, and to show in a state of suspension the substance which is about to be precipitated. The quantity of lime-water which is necessary to be used in this process, when added at intervals, in the manner here directed, is never more than one tenth of the volume of the liquor with which it is mixed; but if the lime-water be all thrown in at once, the lime more than saturates the carbonic acid of the liquor, and the carbonate thus formed, being precipitated, mixes with and weakens the indigo.
In the last described method of producing precipitation, a large quantity of air is introduced into the liquor by beating. This combines with the indigo, rendering it insoluble in water, and forming at the same time a great deal of carbonic acid. The admixture of a small quantity of lime-water after each beating, produces an acidulated carbonate, which remains in solution in the liquor, and a kind of soapy combination with the extractive and vegetoanimal portions of the plant, so that the indigo disengaged from its several combinations can be oxidated and precipitated more easily, and in a state of greater purity.
The first result of this process appears to be a much smaller quantity of indigo than is obtained by employing a volume of lime-water equal to that of the liquor. But the indigo obtained is purer, being equal in quality to the kind which bears the highest price in commerce. This process may be employed in all cases; even when the infusion of leaves is at 122° Fahr. The length of time during which beating must be continued in those cases in which it can alone be employed, is much diminished; and yet the indigo obtained is equally as pure.
When all the indigo has been precipitated, the water is drawn off. The precipitated fecula requires some further operations to bring it to the requisite degree of perfection.
The precipitated indigo still contains a greater or less portion of particles which are not sufficiently oxidated, and consequently it has neither the color nor properties which characterize good indigo. Prolonged beating would, it is true, bring these portions to the desired state; but it would likewise cause those particles which had been first oxidated to imbibe an additional quantity of oxygen, by which their color would bo too much deepened, and indigo of this quality would be rejected in commerce as burnt; it is therefore better to give to the imperfectly oxidated particles the degree of oxidation required, in the following manner.
Stir the liquid fecula strongly, and throw over the whole mass a volume of warm water, double that of the fecula; by this means the perfect indigo will be precipitated, and the other will be held in suspension by the water. This water is to be drawn off and treated with lime-water, by which the green color becomes of a yellow brown, and the indigo being rendered insoluble is precipitated.
It sometimes happens, that the liquor which has been treated with lime-water, and beaten, if the operations have not been well conducted, still retains a portion of indigo in solutiori; this can be ascertained by adding lime-water to a small portion of it, to see if it will become brown.
That indigo may have the purity and brilliancy belonging to it, it must be twice washed, once in cold, and once in hot water.
To perform the first washing, collect all the fecula in an earthen pan, and pour over it four or five times its own volume of very pure water; stir the fecula very carefully, raising it with the hand in the water, and let this be repeated occasionally for several hours, after which it may be allowed to settle; when the fecula is entirely deposited, turn off the water and add more, and let this be repeated till the water is no longer colored. As washing in cold water will not remove all the foreign substances which injure indigo, it is necessary to have recourse to hot Water; but to perform the last washing economically, it is necessary to collect the product of several cold washings, and to operate upon large quantities.
Before commencing the washing in hot water, the fecula receives a certain degree of consistency by compression, after which it is placed in a tub and allowed to ferment during ten or twelve days, till it exhales a strongly acid odor; by this means a mealy portion, which escapes the action of cold water, is decomposed. The process of washing in hot water is next performed in the same manner as I have directed for the cold washing; the operation may, however, be shortened, and very nearly the same results obtained boiling the indigo in water, taking care to stir it the whole time.
To bring indigo to the greatest degree of purity, and to give it the forms which it ought to have in commerce, it must undergo certain other processes.
The washings in water remove all those substances which are capable of being dissolved; fermentation decomposes certain principles which are foreign to the nature of indigo; but there still remain in it, in greater or less quantities, , certain earths, which, according to their several proportions, adulterate it, and which should therefore be extracted; for this purpose the indigopaste is thrown into a vat furnished with two or three stop-cocks situated at various heights, and is there diluted with a large quantity of water. The indigo is carefully mixed with the water; so that all the particles of it may swim separately in the liquid; the upper stop-cock is then opened and the water drawn off into a bucket; the second is then opened, and afterwards the third, and the indigo which the water carries off is allowed to precipitate itself.
As the earthy deposit which is formed at the bottom of the vat contains some indigo, it is washed in a great quantity of water, which is drawn off in the same way as the first, this being repeated till no more indigo can be obtained from the deposit.
Nothing more is necessary to be done to the paste of indigo when it has been freed from all foreign substances, than to separate from it the water which renders it of the consistency of porridge; and for this purpose I shall propose a method which I have practised successfully in some analogous operations. Line the inside of a basket with a coarse bag of woollen or tow cloth, throw the paste into the bag, and leave it to drain. When filtration is ended, cover the paste with the upper end of the bag, which had been turned down, and place upon it a large round wooden dish, which will fit the inside of the basket, and upon this put a weight, which is to be gradually increased till the fecula acquires a great degree of closeness of texture: if the operation be well performed, the mass can scarcely be broken by the hand. This cake is afterwards cut into squares, and dried at a temperature of between 30° and 40°. (Probably of Réaumur, and equal to 99° and 122° of Fahrenheit.) The preparation of indigo is afterwards terminated by an operation which is called sweating.
M. de Puymaurin states, that the most favorable time for operation is when, "upon breaking an angle of one of the cubes, a dry noise is heard." When this is the case, the cakes of indigo are put into a large barrel till it is full, when the top is covered, without having the head fastened in. The indigo remains in this cask three weeks, during which time it heats and gives out a disagreeable odor, it transpires a portion of water, and becomes covered with a white down. At the end of the specified time the surface of the indigo is rubbed and smoothed, and it is then prepared for sale.
The indigo of woad, if prepared with all the care here described, is equal, if not superior to the best of that brought from Guatimala; its effbcts are the same in dying, and it differs from that neither in nature nor in characteristics. By the manufacture of this kind of indigo in France, a new source of agricultural prosperity may be bestowed upon her.
It now only remains to be determined whether or not the farmer can with advantage turn his attention to the manufacture of woadindigo; for without this, though the discovery of the possibility of extracting indigo from the isatis would be in itself an important one, it would be of no use to the nation.
If it should be ascertained that this manufacture would be advantageous in peaceful times, it certainly must be regarded as of great importance at those periods, when a maritime war, by increasing the difficulty of procuring foreign indigo, shall cause the price of it in commerce to be greatly enhanced. Besides, if good king Henry IV. was willing to pronounce penalty of death upon the importers of indigo, in order that he might preserve to agriculture the manufacture of woad cakes, why should not government prohibit the importation of the same article as soon as the manufacture of it from woad is established? France would, by such a course, be endowed with a product of the value of at, least 20, 000, 000: she would be placed above the chances of war, would retain within herself an immense sum which passes into foreign hands, and would furnish employment to the numerous population of the fields.
But let us see if, in the actual state of things, the manufacture of woad indigo can compete with. the importation of it.
An acre of land (old Paris measure) produces at the various cuttings 7½ tons of woad leaves. At the lowest calculation, the product of an acre in leaves, especially in the south, may be fixed at 7½ tons, and that of the indigo which they will yield, at three ounces per hundred weight, will make nearly 28 lbs. of indigo per acre.
The value of good indigo may be estimated at nine francs (a franc being about eighteen or nineteen cents), and this will make the value of the indigo from an acre of land to be 252 francs. Let us now compare this with the value of wheat raised upon the same land: the quantity of wheat may be estimated at about 12 hectolitres ( = 34 bushels), and the price at eighteen francs; this will give 215 francs per acre. We will now calculate and compare the expense attendant upon the cultivation of each plant.
The preparation of the ground by tillage and manures is the same for the seeds of bothplants, but the expense of cultivation and of hand-labor differ essentially.
Weeding by the hand is sufficient for wheat, and the expense of this is very trifling, whilst the same operation when performed upon woad, to which it is much more necessary, must be done with instruments which will loosen the earth, and root out all the noxious herbs: the expense of this cannot be estimated at less than twenty-five francs.
The cutting of the leaves, which must be repeated five or six times, amounts during a season to about fifty francs.
The expenses attendant upon the manufacturing processes cannot be estimated at less than two francs per pound of indigo; this will make fifty-six francs.
The seed necessary for sowing an acre costs about twelve francs, but by leaving the roots in the ground to produce seed, this may be reduced to six francs.
Thus, from the gross product, in indigo, of two hundred and fifty-two francs, there must be deducted
for weeding ... 25 francs
" cutting ... 50 francs
" expense of manufacturing 56 ... francs
" seed ... 6 francs
137 francs
Deducting this from 252 francs, there will remain a net product of 115 francs, (equal to between $21 and $23.)
The expenses attendant upon cultivating and harvesting wheat are not so great as those for woad; for, stating the price of seed at 1/8 of the value of the product, and the weeding, reaping, gathering in, and threshing, at 1/6, the whole expense would be but sixty-three francs, and this reduces the net value of the product to one hundred and sixty-three francs; the balance would thus be in favor of the cultivation of wheat.
It must, however, be remembered, that stated the value of the product in indigo at the lowest. M. de Puymaurin has obtained five ounces, and that of a good quality, from 1 cwt. of leaves; at this rate an acreof land would yield forty-seven pounds of. indigo, instead of twenty-eight; and this sold in commerce even at the low price of six francs, would produce two hundred and eighty-two, instead of two hundred and fifty-two francs. An additional profit likewise arises from the cakes into which the leaves are formed after having been nearly exhausted of their indigo; these may be sold with advantage to the dyers, or if there be no demand of this kind for. them, they form a better and more abundant manure than that which is yielded by the dried stalks and leaves of wheat.
I may likewise add, that in those establishments which are in the vicinity of dye-houses, the indigo paste, which produces the same effect as the indigo cakes, may be sold, and thus the manufacturer may save himself the performance of the three principal operations, filtration, drying, and sweating; and the dyer will be spared the trouble of breaking the cakes. I am even assured, that by making use of the fecula, instead of the indigo, which has gone through all the processes, the dyer can diminish the quantity of woad cakes which he uses in the composition of his coloring liquor.
It seems very evident to me that the introduction of this valuable branch of industry into our country, needs only some slight encouragement on the part of government; the only one I would ask is, the augmentation of the present duty upon imported indigo of ten francs per kilogramme, (about 80 cts. per lb.) Without this, the agriculturist can hardly determine to undertake a manufacture, which, though promising advantage, is new to him, and, if badly conducted, presents, like all others, danger of loss.
I shall conclude this chapter by inviting all agriculturists who are zealous for the progress of their art, to undertake the cultivation of the isatis tinctoria upon a very small portion of their ground, and in a soil suited to it, for the purpose of making indigo; they may in this way familiarize themselves with the processes of the manufacture so as to be able to enter into it upon a large scale with confidence.
The isatis grows and prospers in all climates; that which is raised in the northern departments of our country has been known to yield five ounces per cwt. which corresponds to the quantity afforded by it in the south.
It would be wrong to be discouraged in any undertaking by the failure of a first attempt; neither in cultivation nor in manufacturing can one hope to arrive at perfection at once; time, experience, and especially close observation, can alone enable us to overcome all obstacles, and so to manage our concerns as to be always sure of success. The experiments which I recommend are not costly, neither do they require any other utensils than are to be found in every farm house.
