Wool Dyeing. Lecture I. (Continued)
Purification and Correction of Waters which are to be used in the Treatment of Wool.
Wool bleaching

Practical Magazine 23, 1876

Pidempi artikkeli jaettu erillisiin osiin.

(Chemistry applied to the Arts, Manufactures, &c.)

A course of Lectures by George Jarmain.

Purification and Correction of Waters which are to be used in the Treatment of Wool.

The treatment of water, which is required in such large quantities, for the scouring and dyeing of wool and woollen cloths is always troublesome, costly, and unsatisfactory at the best; and it is advisable to avoid all such treatment, when possible, by obtaining the water from another source, or even by removing to new premises where suitable water is obtainable.

In case, however, no such course is practicable, the following processes may be employed, in order that the evil effects of unsuitable water may be mitigated: —

1. — Exposure to Air, Subsidence, and Filtration.

When the impurities consist of matters in suspension or of bicarbonate of iron, exposure to air in a shallow reservoir and subsequent filtration through a bed of sand will generally be found sufficient. The iron will be oxidised and rendered in soluble, and is then capable of removal by filtration. I have seen its removal effected satisfactorily by passing the water through a bed of shoddy, which acts as a very good filter.

2. — Treatment with Lime and Subsidence (Clark's Softening Process).

This treatment is only applicable to water that contains chalk, carbonate of magnesia, or iron salts in solution. The lime combines with the carbonic acid, which holds the carbo nates of lime and magnesia in solution, which are thus rendered insoluble, and precipitate along with the lime added. This mode of treatment is theoretically very perfect, but there are practical difficulties in the way of treating large masses of water which render it very difficult to manage. If too little or too much lime be added the water is often made worse, and the point at which sufficient lime has been added is not very easy to determine. If a day's consumption can be treated at one time the proper quantity of lime to use can be determined by treating separate small quantities of the water with known but varying weights of lime, and after allowing it to subside over night that proportion which has softened the water most can be determined by the soap test. The quantity of water for a day's consumption should be treated with the calculated weight of lime, which should be mixed with water, and run into the reservoir, and the whole must then be agitated. This should be done at the close of the day; the carbonates will have subsided before morning. Water thus treated is very bright and clear, and if managed successfully will be found to be moderately well adapted for the treatment of wool.

3. — Treatment with a Ferric Salt, and then with Carbonate of Soda.

This method is well adapted for the removal of soluble organic impurities and suspended fine clay. It has been applied by Dr. Gunning with great success to the turbid waters of the River Meuse. For the treatment of 3,000 gallons, 1 lb. dry perchloride of iron is dissolved in water and then thoroughly mixed with the bulk; I lb. of soda ash of 52 per cent. is then dissolved, run in, and the whole again agitated. The hydrated peroxide of iron deposits, carrying down with it the organic impurities, common salt being the only substance left in solution.

4.–Treatment of Permanently Hard Waters (Wanklyn's Method).

As has already been explained, these waters contain the sulphates of lime and magnesia, which have always proved to be the most difficult of removal. Mr. Wanklyn has recently proposed to soften waters of this class by first adding bicarbonate of soda and then lime. The bicarbonate of soda first converts the sulphate of lime into bicarbonate of lime, and the subsequent addition of lime precipitates the bicarbonate so formed. sulphate of soda remains in solution in the water.

I have not had an opportunity of seeing this process tried on a large scale, but I consider it likely to accomplish the end in view, if its cost should not prove to be a bar to its use.

5. — Treatment of Hard Waters with Soap.

If hard water must of necessity be employed for scouring with soap, it is advisable to separate the hardening matter by mixing a sufficient quantity of a hot solution of soap with it, and then causing it to run through a filter-bed before use. The insoluble soaps will thus be separated without attaching themselves to the wool or fabric, and they may be collected and treated with hydrochloric acid, to decompose them and separate the fatty acids, which may then be collected and reconverted into soap by boiling them up with caustic, or even carbonate of soda, and the soap thus obtained may be used again for the same purpose. Water thus treated is well adapted for the scouring of wool and woollen goods.

6. — Treatment and Correction of Waters in the Dye-bath.

Organic matter, oxide of iron, and often a considerable proportion of the hardening matter, may be caused to rise to the top, and may then be skimmed off, by dissolving alum in the water in the proportion of about 4 oz. per 1,000 gallons, and then raising it to near its boiling point.

In preparing waters which contain alkaline or earthy carbonates or bicarbonates as a bath for either mordanting or dyeing, they should be treated with sufficient sulphuric acid to expel all the carbonic acid, and to neutralize any alkali which may have escaped washing out from the scour.

The use of bran is frequently serviceable in removing impurities from water in the bath.

Purification of the Refuse Waters from Woollen Mills.

In concluding my remarks on the subject of water, I beg to draw attention to the fact that the refuse waters from a woollen manufactory contain within themselves the elements of their own purification. At the present time the practice is to turn these refuse waters into the river-courses as they are done with. Sometimes mordant-baths are run out, at other times the spent dye-baths, and soap, or alkaline fluids. These mingle in the common receptacle, the river, and precipitate each other there, thus producing those black deposits which give to our streams in the woollen districts such an inky and foul appearance. I have mixed together solutions of all the substances used in our woollen industries, and find that they precipitate one another, and leave the supernatant water in a tolerably clear condition. The remedy seems to be, so far as the woollen trade affects the purity of the rivers, to run all the liquids into one common reservoir, and, after subsidence, to pass, if necessary, the supernatant water through a filter-bed into the river. The utilization of the black muddy deposit would, I believe, speedily follow.


I have now to draw your attention to the cleansing of wool and woollen fabric, in preparation for its subsequent treatment in the dye-house.

Raw wools always contain a considerable amount of organic and earthy impurities. The most abundant of these is suint, a peculiar organic body containing, potash. M. Chevreul gives the following as the composition of merino wool: —

Earthy matter ... 26.06
Suint ... 32.74
Greasy matter ... 8.57
Earthy matter fixed by the grease ... 1.40
Clean wool ... 31.23

I am not aware that any attempt has been made in England to utilize the wool impurities. A very pure potash salt is, however, manufactured from them in France.

Scouring Materials.

The following are the detergents in use in the woollen industry: - Urine, ammonia, soda ash, soda crystals, soap (hard and soft), silicate of soda, and various compositions containing carbonate of soda.

Many manufacturers prefer to use stale urine, which contains a considerable quantity of carbonate of ammonia, a particularly mild alkali. The organic matter in the urine appears also to assist in cleansing, and it protects the woollen fibre from injurious action by alkalies.

Ammonia is also a mild alkali, and, for the treatment of wool, that distilled from urine is preferred to all other kinds. The strength of ammonia is determined by taking its specific gravity by means of a hydrometer, called an ammoniameter. The one in common use in Yorkshire and Lancashire has an arbitrary scale, each degree equalling 3, water being taken at 1.000. Thus, the specific gravity of ammonia at 20° equals 1.000– (20 x 3) = 940. The crude ammonia distilled directly, from gas liquor frequently contains hydrocarbons and sulphide of ammonium. The former can easily be recognized by pouring some of the ammonia on a plate; after a few hours, when the ammonia has passed away, the tarry smell of the hydrocarbons will be perceptible. Sulphide of ammonium is readily distinguished by the dark colour which the ammonia gives when treated with a solution of acetate of lead, or by the blackening of a silver coin when dipped into it, the black sulphides of lead and silver being formed respectively.

The hydrocarbons act strongly on the skin of the workman, and the sulphides act injuriously on the wool.

Carbonate of soda is the most extensively used scouring agent; it enters largely into the composition of many detergents bearing fancy names. The following are the principal forms in which it is employed in the woollen manufactory: — Soda ash, containing from 30 to 52 per cent, available alkali; (oxide of sodium) soda crystals, containing 21.7 per cent available alkali; soap ash, containing 21.7 per cent. available alkali and a small quantity of soap or palm oil; dry soap (good), containing 2/3 carbonate of soda and 1/3 soap; urine substitute, melted soda crystals.

The value of these substances as detergents is in proportion to the available alkali (oxide of sodium combined as carbonate) which they contain. Dry soap, however, contains in addition a considerable quantity of soap.

I have occasionally seen the workman gauging the strength of his soda ash liquors by means of a hydrometer; this is a foolish plan, because the salt and other impurities contained in weak soda ash add to the density of its solution and give to it a fictitious strength.

It is important that the foreman should know what is the available strength of the soda ash he employs. I have found the following plan to give sufficiently accurate results in the hands of an intelligent workman:

Apparatus required. – One burette, 50 cubic centimetres in 1/5; one holder for ditto; one 100 cubic centimetres graduated measure; one litre measure; one box scales and weights to weigh to 1/10 of a grain; one boiling flask; one filtering funnel and filter paper; one spirit lamp, or Bunsen burner where gas is in use; one retort or tripod stand, and a piece of wire gauze; infusion of litmus; one ½-oz. porcelain crucible; one 4-oz. beaker glass. Most of these are included in the soap test apparatus.

Two standard solutions are required, viz., standard sulphuric acid, and a solution of caustic soda which exactly neutralizes an equal volume of the standard sulphuric acid.

The acid is made of such a strength that 1 cubic centimetre of it neutralizes ½ grain of oxide of sodium (soda).

The preparation is as follows: – About 200 grains of pure carbonate of soda, or, failing that, Howard's bicarbonate, are heated to redness for an hour in the porcelain crucible over the lamp, to expel moisture, &c. When cold, weigh out carefully 171 grains of it, dissolve it in a little distilled water in the beaker, pour it into the 100 cubic centimetres measure, rinsings as well, and make up to 100 cubic centimetres with distilled water; pour into a bottle and add to it another 100 cubic centimetres of distilled water.

Every cubic centimetre of this solution contains ½ grain of oxide of sodium, and is used to prepare an acid solution of equal strength — the standard sulphuric acid.

The acid is prepared in the following manner: About half fill the litre measure with distilled water, pour into it 31 cubic centimetres of strong sulphuric acid, D. O. V. 170° Tw., fill up to the litre mark with distilled water, then pour into a bottle to mix it. This acid will be too strong, and will require an additional quantity of water; its actual strength, as compared with the prepared solution of carbonate of soda, must now be ascertained. Pour 100 cubic centimetres of the standard carbonate of soda solution into the boiling flask, add another 100 cubic centimetres of distilled water and a few drops of the litmus; fill the burette up to the top mark with the diluted sulphuric acid, and run it into the flask until the litmus begins to redden; then boil to expel carbonic acid: run in more of the sulphuric acid in repeated small quantities until the blue colour begins to per manently redden, boiling after each addition. When the exact point has been reached, read off the number of cubic centimetres which have been used; if, say, 94 cubic centimetres of the diluted acid have been used, then the acid of the proper strength will be made by adding 6 of water to 94 of the trial acid; in order that this mixture may be made, pour 60 cubic centimetres of distilled water into the litre measure, fill up to the mark with the trial acid, and mix as before by pouring it into a bottle. This is the standard sulphuric acid, every cubic centimetre of which neutralizes half a grain of oxide of sodium, and which alone will enable the workman to test his soda ash and other materials depending for their value upon the available oxide of sodium they contain.

The process is as follows:–Weigh out 50 grains of the ash, put it into the flask with 100 cubic centimetres of distilled water, and heat until dissolved; filter; if any portion remains undis solved, wash the filter, add a few drops of litmus liquid, run in the standard sulphuric acid from the burette, and find the neutral point as before, boiling between each addition of acid until the litmus shows signs of reddening. Read off the acid taken; the number of cubic centimetres of acid required is the percentage of available alkali contained in the soda ash examined, no calcu lation being required; for each cubic centimetre of the acid ºliº half a grain of oxide of sodium, and 50 grains were taken.

The operation may be shortened, and made more exact, by using a second standard solution, viz., one of caustic soda, which contains half a grain of oxide of sodium per cubic centimetre. This solution is prepared by testing with the standard acid a solution of caustic soda made a little too strong, and then diluting it to standard strength in the same manner as was done with the sulphuric acid.

To test a sample with the two solutions, weigh out 50 grains, and dissolve, with the precautions given above; measure into it an excess of standard acid, say 60 cubic centimetres, if a strong soda ash be under examination; boil until all carbonic acid is expelled, add a few drops of litmus, which will redden if the proper amount of acid has been added, then neutralize the excess of acid by running into it from the burette the standard solution of caustic soda until the red colour begins to change to blue. The number of cubic centimetres of caustic soda required to do this is a measure of the excess of acid used; the percentage of available alkali is, therefore, ascertained by deducting the cubic centimetres of caustic soda from the cubic centimetres of standard acid used; the remainder represents the available alkali.

The following is an example:–50 grains of soda ash were dissolved in hot water and filtered into a flask, and 60 cubic centimetres of standard acid were added, and the whole boiled for ten minutes. Litmus was then added, and it was found that it required 8 cubic centimetres of standard caustic soda before the blue colour of the litmus was restored. The percentage of available alkali was, therefore, 60 — 8 = 52 per cent.

The process given above determines the true percentage of available alkali, and does not take account of the absurd standards which trade customs sanction in Liverpool and Newcastle.

The advantages derived from being able to ascertain the amount of alkali in a detergent are: —
1. The manufacturer knows when he gets his money's value.
2. The workman knows when he is using the right quantity of materials.

Soap. –Soap consists of a fatty acid in combination with potash or soda, water, and impurities of no detergent value, or positively injurious. The value of a soap depends upon the amount and correct proportions of fatty acid and alkali. The former is determined by weighing out 50 grains of the soap, and boiling it in a beaker glass in distilled water till dissolved, adding 10 grains of solid paraffin, and then about 10 cubic centimetres of sulphuric acid, diluted in a little water; the whole is then boiled gently until the liquid clears, and the oily matter completely rises; it is then set aside till quite cold, when the fatty acid can be removed in a cake, dried upon blotting-paper, and weighed. The weight, from which the paraffin added must be deducted, gives the fatty acid, the double of which, if 50 grains have been taken, is the percentage.

The percentage of soda can be obtained in the same manner as is used for soda ash. In soft soaps, which contain potash instead of soda, the potash (oxide of potassium) is obtained by multiplying what is obtained by the soda process by 1,516, or roughly calculating for potash half as much more as the soda indication. The equivalent of potash is 94 and that of soda is 62.

Silicate of Soda. - This material is coming into favour as a detergent; it cleanses wool very satisfactorily, and leaves it in a suitable condition for the reception of dyes, particularly those of the aniline colours.

Wool Scouring.

The detergents used are, soft soap for fine long wools; and for short wools, both coarse and fine, urine alone, or urine and soda ash, or soda ash alone, silicate of soda, and various mixtures of alkaline carbonates and soaps.

The best temperature for the scouring of loose wool is from 125° to 135°Fahr.

The old-fashioned mode of scouring wool, and which gives fair results, is to work it about in a kettle or tub containing the scouring liquid with a stick or stang for five or ten minutes, and then lift it out upon a scray with the stang or a fork, by small portions at a time. When it has drained upon the scray it is thrown into a cistern called a "wash-off," the bottom of which is fitted with perforated iron plates. Water is then run into the cistern by a five or six inch pipe entering horizontally, and when full the wool is stirred up well in it. The water is then let out from under the perforated plates by means of a clack. The washing with water is repeated two or three times. This method requires an abundant supply of water, but is in other respects economical. An improvement upon this process, very often resorted to, is, to have a perforated sheet iron shell swung on a trunnion and fixed to a crane. The shell is lowered down into the scouring pan, and the wool scoured in it; when ready, it is drawn out by the crane and the wool thrown out into the wash-off cistern by tilting the shell over. The wool is washed two or three times as before. One man can scour from 500 lbs. to 600 lbs. per day by the first mode; it requires two men to scour by the perforated shell, but more work can be got through.

For certain classes of wool, in which soap is employed as the detergent, the scoured wool is passed between rollers instead of washing it.

Long stapled wools are manipulated with forks by hand in the scouring fluid.

In most large factories, however, the above processes for cleansing wool from their natural impurities have been superseded by the introduction of wool-scouring machines, the first of which which was invented in 1851, by Mr. John Petrie, jun., of Roch dale, who has since that time very greatly improved the machine; in fact, the latest form of it, the "Paragon," as he calls it, leaves little to be desired.

A complete machine consists of three boxes or bowls. The wool is fed into the first by a boy. In this bowl a strong scour is placed, through which the wool is forked by forks ingeniously fixed to cranks; from this bowl it is passed through rollers into the second, which contains a weaker scour; it then passes through rollers to the third, in which it is forked through running water; and lastly passes between heavy squeezing rollers and is thrown forward by a powerful fan, which leaves it light and open. The wool is turned out very clean and half dry. In fact the machines perform a large amount of work in a very satisfactory manner, and the manufacturers who use them tell me that they are very much pleased with them. McNaught’s and Leech's machines, each possessing special features of its own, are also spoken well of by those who use them.

Yarn Scouring.

The impurities to be removed by scouring from woollen yarns are, oil, which has been used to enable the wool to be scribbled and spun, and accumulated dirt. The detergent used is a mixture of soap and ammonia, but for some descriptions of yarns cheaper alkaline liquids may be used.

It is important that the felting of the yarn should be avoided as much as possible. This may be accomplished by steeping the yarn in hot water and leaving it to cool before scouring.

The scouring is done in a wood cistern filled with the scouring fluid; the yarn is hung on Sticks placed across the cistern, it is turned over frequently, and worked about in the scour, and finally wrung out. The best temperature for the yarn scour is from 140° to 150°Fahr.

Cloth Scouring.

This is always done in a machine consisting of a bowl or cistern, and squeezing rollers placed above. The scouring ma terials vary with the description of cloth — soda ash, soda crystals, and soap ash being usually employed for woollen cloths. The cloth passes through the scouring liquid heated to from 150° to 160°Fahr., and then between the rollers for some time, whereby the oil contained in the cloth is removed in the form of an emulsion by the detergent. The scour is frequently used again, after being strengthened by the addition of more alkali. The cloth is finally washed in clean running water on the machine for a considerable time. The thorough removal of all oil, soap, and grease from the cloth is very important for the subsequent dyeing, for if any remain in it the action of the mordant is seriously interfered with.

Wool Bleaching.

The mode of bleaching woollen goods in general use at the present day is of a very primitive character, there having been but little improvement in the process since the days of Pompeii, in the ruins of which, Pliny tells us, there were found traces of the art. As in those days, so now, a closed chamber, in which the goods to be bleached are hung up, is filled with the fumes of burning sulphur, and the goods left exposed to the action of these sulphurous fumes for some hours, during which time the yellow colouring matter of the wool is more or less affected, probably by the reducing action of the sulphurous acid, whereby the colouring matter is transformed into a colourless substance. The bleaching, however, is not of a very permanent character, the colour being liable to return, especially if the goods are treated with alkaline solutions, which frequently favour oxidation. The bleaching of wool with sulphurous acid is, therefore, not so satisfactory as the bleaching of cotton with chlorine.

Chlorine is not suitable for the bleaching of wool, for it attacks and damages the fibre without bleaching it. Sulphurous acid is the only bleaching agent which has proved effective for wool. The operation is called "sulphuring," or "stoving." The sulphur stove is built of brick or stone, and often lined with wood, as few nails as possible being used, to prevent damage from sulphate of iron, which is formed by the sulphurous acid, combined with air, acting upon the nails. The goods to be bleached are well soaped and washed, and while in a moist condition are hung up in the room. A quantity of sulphur is placed in an iron dish in the room, and a red-hot piece of iron is dropped among it; the door is then closed, and the room left undisturbed for some hours. The door is then thrown open, and the sulphurous acid gas es capes; the goods are then removed, and washed, to free them from the sulphurous acid, which, if left in contact with the fibre, would become sulphuric acid by the oxidising action of the air.

Certain improvements have been suggested in the management of these sulphur chambers, having for their objects economy in the use of sulphur; the more equal diffusion of sulphurous acid in the chamber, and, consequently, more regularity in its action; and, lastly, prevention of the destructive action on vegetation arising from the escape of the sulphurous acid on opening the door. In the "Moniteur de la Teinture" for 1872 an arrange ment is described which is likely to accomplish this object. Sulphurous acid, produced in a sulphur burner, is forced into the chamber by means of a small steam jet, and when the goods . have been exposed in the room for the proper time the sulphurous acid is drawn out by an aspirator and is absorbed by carbonate of soda, which it converts into sulphate of soda. An additional improvement consists of an arrangement for passing the goods through the chamber by means of rollers. The bleaching of cloth can thus be made continuous.

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