Chapter IV (5)

Of late years, under the names of Azophor red P N, Nitrazol C, Nitrosamine, etc., there has been offered to dyers preparations of diazotised paranitroaniline in the form of a powder or paste, readily soluble in water, that will keep in a cool and dry place for any reasonable length of time. These are prepared in various ways, and to any dyer who does not want the trouble of diazotising the paranitroaniline they offer some advantages. They produce a red equal in every respect to that obtained from paranitroaniline. The following details show the method to be followed with some of these products, others are very similar to make the developing baths.

_Paranitroaniline Red with Nitrazol C._--Dissolve 25 lb. Nitrazol C in 12 gallons of cold water with constant stirring, then add sufficient cold water to make 37 gallons. In another vessel dissolve 11 lb. of acetate of soda in 5-1/2 gallons water, then add 1-1/2 gallons caustic soda, 36° Tw., mixed with 5-1/2 gallons water. The developing bath is made by mixing both these solutions. It will suffice for both yarn and piece goods.

_Paranitroaniline Red with Azophor Red P N._--Dissolve 5-1/2 lb. of Azophor red P N in 4 gallons of water--it dissolves almost completely but usually a few particles of a flocculent character remain undissolved, these can be removed; 2-1/4 gallons of caustic soda lye of 36° Tw. are diluted with water to 10 gallons, and this is added with constant stirring to the azophor red P N solution. When all is mixed and a clear solution obtained, the developing bath is ready for use, and is used in the same way as the paranitroaniline bath.

_Metanitroaniline Orange._--This orange is produced in the same way as the paranitroaniline red, using metanitroaniline or Azophor orange M N in place of the paranitroaniline or the Azophor red P N given for the red. The quantities of all the materials used are identical.

_Nitrosamine Red._--Dissolve 5 lb. Nitrosamine red in 5 gallons of water and 2-1/4 lb. hydrochloric acid, when well mixed there is added 2-1/2 lb. acetate of soda, when all is dissolved add sufficient water to make 6-1/2 gallons. This bath is used exactly in the same way as the paranitroaniline developing bath, and it produces identical results in every way.

_Paranitroaniline Brown._--By boiling the paranitroaniline red dyed cotton in a weak bath of copper sulphate a very fine fast brown resembling a cutch brown is produced. A better plan, however, is to prepare the cotton with a ground containing an alkaline solution of copper, 3 lb. beta-naphthol are dissolved in 5 pints of caustic soda lye of 36° Tw., to which is added 5 lb. Turkey-red oil and 10 pints alkaline copper solution, water being added to make 13 gallons of liquor. The cotton is treated in this way as with the ordinary beta-naphthol preparation. The alkaline copper solution is made by taking 5 pints of copper chloride solution at 76° Tw., adding 3-1/4 lb. tartaric acid, 6 pints caustic soda lye, 70° Tw., and 2 pints of glycerine. The developing bath for the brown is the same as for the paranitroaniline red, or the Azophor red P N bath may be used.

_Toluidine Orange._--For this colour the cotton is prepared with the beta-naphthol in the ordinary way. The developing bath is made from 2 lb. orthonitrotoluidine mixed with 12 pints boiling water and 2-1/4 pints hydrochloric acid; when dissolved allow to cool and then add 12-1/2 lb. ice. When thoroughly cold stir in 2-1/2 pints of sodium nitrite solution containing 3 lb. per gallon. Stir well for twenty minutes, then filter; add 4 lb. sodium acetate and sufficient ice-cold water to make 13 gallons. Use this bath in the same way as the paranitroaniline bath.

_Beta-naphthylamine Red._--This red is a good one, but is not so bright or so fast as the paranitroaniline red, hence although somewhat older in point of time it is not dyed to the same extent. The developing bath is made from 1-3/4 lb. beta-naphthylamine dissolved with the aid of 10 pints boiling water and 1 pint hydrochloric acid. When dissolved allow to cool; add 27 lb. ice and 2 pints hydrochloric acid. When cooled to 32° to 36° Tw., add 3 pints sodium nitrite solution (3 lb. per gallon) and 4 lb. sodium acetate, making up to 13 gallons with water. This also is used in precisely the same way as the paranitroaniline red developing liquor.

_Alpha-Naphthylamine Claret._--This is a very fine and fairly fast red, and next to the paranitroaniline red may be considered the most important of the naphthol colours. The developing bath is a little more difficult to make, owing to the fact that it is more difficult to get the alpha-naphthylamine into solution. The best way of proceeding is the following: Heat 1-3/4 lb. of alpha-naphthylamine in 10 pints of boiling water, agitating well until the base is very finely divided in the water, then 1-1/4 pints of hydrochloric acid is added, and the heat and stirring continued until the base is dissolved, then the mass is allowed to cool, 27 lb. of ice is added and 1-1/2 pints of hydrochloric acid. When cooled down to 32° to 36° F., there is added 3 pints sodium nitrite solution (3 lb. per gallon), and after allowing the diazotisation to be completed, 4 lb. sodium acetate and sufficient water to make 13 gallons of liquor.

The bath is used in the same manner as the previous developing baths.

_Dianisidine Blue._--Dianisidine develops with beta-naphthol, a violet blue, which is not very fast, but by the addition of some copper to the developing bath a very fine blue is got which has a fair degree of fastness. The developing bath is made as follows: Mix 10-1/2 oz. dianisidine with 7 oz. hydrochloric acid and 7-1/2 pints of boiling water, when complete solution is obtained it is allowed to cool, then 20 lb. of ice is added. Next 1-3/4 pints of nitrite of soda solution, containing 1-1/2 lb. per gal. and 2-1/2 pints of cold water. Stir for thirty minutes, then add 1-1/4 pints copper chloride solution at 72° Tw., and sufficient water to make up 6-1/2 gallons.

The cotton is prepared with beta-naphthol in the usual way, and then passed through this developing bath.

_Amidoazotoluol Garnet._--Amidoazotoluol produces with beta-naphthol a fine garnet red in the usual way.

The developing bath is made from 14 oz. amidoazotoluol, mixed with 1-1/2 pints of sodium nitrite solution containing 1-1/2 lb. per gallon, when well mixed add 1 pint of hydrochloric acid diluted with 2 pints water, when this is well mixed add sufficient water to make up a gallon, then add 1 lb. acetate of soda.

The cotton is passed through this dye-bath, then washed well, passed through a weak acid bath, then soaped well, washed and dried.

(8) DYEING COTTON BY IMPREGNATION WITH DYE-STUFF SOLUTION.

Indigo is a dye-stuff which requires special processes for its application to the cotton or wool fibre.

Its peculiarity is that in the form in which it comes to the dyer it is insoluble in water, and to enable it to be dissolved and therefore to be used as a dye, the indigo has to go under a special treatment. The colouring principle of indigo is a body named indigotin, to which the formula C{16}H{16}N{2}O{2} has been given. When indigo is mixed with substances like lime and copperas, lime and zinc, zinc and bisulphite of soda, which cause the evolution of nascent hydrogen, it takes up this body and passes into another substance which is called indigo white that has the formula C{16}H{12}N{2}O{2}, leuco, or white indigo; this substance is soluble in water, and so when it is formed the indigo passes into solution and can then be used for dyeing. But indigo white is an unstable substance on exposure to air, the oxygen of the latter attacks the hydrogen which it has taken up, and indigotin is reformed, the indigo white changing again into indigo blue.

Indigo dyeing consists of three operations:--

(1) Preparation of the indigo solution, or, as it is called,
setting the dye vat. (2) Steeping the cotton in this vat. (3)
Exposing to the air.

There are several methods of preparing, or setting the dye vat, and of each of these modifications are in use in every indigo dye-house:--

(1) With lime and copperas. (2) Zinc and lime vat. (3) Zinc and
bisulphite of soda.

In all cases it is necessary for the indigo to be ground to the form of a fine paste with water; this is usually done in what is known as the ball-grinding mill. The finer it is ground the more easy is it to make the dye-vats.

The dye-vats may be either round tubs or square wooden tanks; when cloths or warps are being dyed these may be fitted with winces and guide rollers, so as to draw the materials through the liquor. In the case of yarns in hanks these appliances are not necessary.

Fig. 30 is a sketch of an indigo dye-vat for cloth or warps.

(1) =Lime and Copperas Vat.=--To prepare this vat take 75 gallons of water, 4 lb. of indigo, 8 lb. copperas, and 10 lb. of good quicklime. Put these into the vat in the order shown. The amount of indigo is added in proportion to the shade which is required to be dyed: for pale shades, 2 lb. to 3 lb. will be sufficient; while for deep shades, 6 lb. to 7 lb. may be used. The amount of copperas should be from one and a half to twice that of the indigo. The vat should be stirred very well and then left to stand. The changes which occur are probably the following: The lime acts upon the copperas and produces ferrous hydrate--this is unstable and tends to take up oxygen and hydrogen from the water, particularly when there is some indigo present, and forms ferric hydrate; hydrogen is at the same time liberated, and combines with the indigo to form the soluble indigo white. It takes about twenty-four hours to make an indigo vat. When properly made and in good condition, the liquor will be clear and of a brownish-yellow colour, a bluish scum may collect on the surface. If the liquor appears at all greenish it is an indication that the indigo has not been completely reduced, and the vat needs a further addition of lime and copperas, which should be of good quality. Too much of each should not be used, because with them there is formed at the bottom of the vat a sediment of calcium sulphate and ferric hydrate, and it is not wise to increase this to too great an extent, which would be the case if too much lime and copperas were added.

_To Use this Vat._--Any scum on the surface is raked on one side, the cotton yarn immersed for a few minutes, then it is taken out, wrung, allowing the excess liquor to flow back into the vat, and the yarn hung up in the air for the blue to develop. The depth of shade which is dyed depends chiefly upon the amount of indigo in the vat, and also upon the time during which the hanks are dipped in the liquor. Light and medium shades can be readily and conveniently got by a single dip, but deep shades are best got by repeating the dipping once or twice as occasion demands. Deep shades got by using a strong bath at a single dip are found to rub badly, while by repeated dips the dye gets more into the substance of the fibre, and therefore the colour is more firmly fixed and it rubs less.

Some indigo dyers have quite a range of vats, using those fresh made for dyeing deep shades, while the old vats being nearly exhausted are used only for light shades and finally when completely exhausted are thrown away. After the day's work the vat should be stirred up and then allowed to stand. If necessary it may be strengthened by the addition of fresh quantities of indigo, lime and copperas, the next morning it will be ready for use. Generally a lime-copperas vat will remain in good working order for about a month, when it will be necessary to throw it away.

=(2) Zinc and Lime Vat.=--Zinc dust is a bye-product in the process of zinc extraction. It is a grey, very heavy powder, consisting mostly of finely divided metallic zinc, with traces of oxide and sulphide of zinc. Of these only the metallic zinc is active in reducing the indigo, the rest of the ingredients are not of any consequence. The valuation of zinc dust is a very difficult operation, but it is desirable that this be done, as the product is liable to be very variable in the proportion of actual zinc it contains, and it will pay large buyers always to have it tested. Zinc dust must always be kept in a dry place.

For the reduction of zinc powder lime is chiefly used. The following are two good mixtures.

Vat with zinc and lime:--

10 lb. indigo, dry and ground fine; 5-1/2 lb. zinc dust; 22 lb. slaked lime, dry.

The vat is set as follows, a part of the lime is mixed with the indigo, and the two bodies are well mixed together and allowed to stand for ten minutes, then the zinc powder is added. It is best to make this into a smooth paste with water before adding it to the other ingredients, then the rest of the lime is added and the whole is thoroughly stirred together with the necessary quantity of water.

Vat with zinc powder, lime and soda:--

10 lb. indigo, dry and ground fine; 10 lb. zinc powder; 10 lb. slaked lime, dry; 35 lb. caustic soda at 11° Tw.

Add the lime to the ground indigo, then add the zinc and finally the soda lye.

Soon after the various ingredients of the vats are added together the whole mass becomes hot, when it must be well stirred. It soon begins to evolve gas and the mixture froths. In from two to four hours the evolution of gas ceases. The dark blue solution now becomes yellow and the liquor shows all the characteristics of the indigo vat. It is necessary to keep the vat well stirred up during the time of setting, which takes from five to six hours. If there is much evolution of gas after this time it indicates that too much zinc powder has been added; this is a common fault with dyers, and such excess causes the vat to be too much disturbed and to work dirty. A lime-zinc vat, with occasional additions of new materials, keeps good for three months, and even then is in a better condition than the copperas vat.

This vat is used in precisely the same way as the copperas vat; as it contains no sediment, or but little, it works cleaner than the copperas vat and as a rule the indigo blues dyed in it are faster to rubbing.

After a day's work it can be well stirred up and fresh additions of lime, zinc and indigo made to bring it up to its original dyeing strength.

=(3) Zinc-Bisulphite Indigo Vat.=--When zinc dust and bisulphite of soda are mixed together a reaction sets in, the zinc dissolves, and there is formed sodium hydrosulphite and zinc and sodium sulphites. If now indigo is mixed with this solution the sodium hydrosulphite exerts a reducing action on it, forming white indigo and sodium sulphite, a perfectly clear solution being obtained, which may be used in dyeing cotton or wool.

With this vat it is customary to prepare a strong stock solution of reduced indigo, and to add this to the dyeing vats as may be required.

_To Make the Stock Liquor._--Take 20 lb. of indigo, grind into a paste with 20 gallons of boiled water, then add 25 lb. lime slaked into a milk. In a separate tub there is mixed 80 lb. bisulphite of soda, 70° Tw., with 9 lb. zinc dust; this mixture is well stirred and every care taken to prevent it getting hot. When the zinc has dissolved and the mixture is free from any sulphurous smell it is run into the indigo mixture given above. The whole is well stirred together for some time, and then at intervals, until the indigo has become dissolved, sufficient water is added to make up 50 gallons, when the stock liquor will be ready. It should have a deep yellow colour. The surface may have a scum of a bronzy colour collect on it. This stock liquor should be kept in casks free from exposure to the air.

To make the working vat from this stock liquor the following is the method of proceeding:--

Water is run into the vat, and this is heated from 70° to 80° C. in order to expel air from it, after which it may be allowed to cool, then for each 1,000 gallons contained in the vat there is added 30 lb. bisulphite of soda, 3 lb. zinc dust and 3 lb. lime, made into a cream. When all these ingredients are dissolved a quantity of the stock liquor is added in proportion to the shade that it is desired to dye. The whole is well stirred, then the vat is allowed to rest for half an hour to enable any sediment to settle, and then the dyeing is proceeded with.

Should the vat show signs of becoming green in colour it is a good plan to add a mixture of 1 lb. zinc dust and 10 lb. bisulphite of soda. The vat should be kept alkaline, and so a little lime may be added from time to time.

After a day's work it is well to add a little of the zinc and bisulphite mixture, to stir well and allow to stand overnight; the next morning strengthen up the vat by adding fresh stock liquor.

In place of using lime in making up the vat it is possible to use a mixture of caustic soda and ammonia. The lime will tend to cause some sediment to form in the vat, whereas the soda and ammonia will not. When they are used the following mode of working may be followed:--

_Stock Liquor._--Soda zinc vat: Put in a tub 26 gallons cold water, 15 lb. zinc powder ground into a paste with 6 gallons water, then stir in 8 gallons bisulphite of soda at 60° Tw., stir well, keeping the heat down as much as possible, after which add 8 pints caustic soda lye at 70° Tw. and 14 pints 20 per cent. liquor ammonia. When all is thoroughly mixed add 30 lb. indigo, ground into a paste with 7 gallons water, allow to stand for half an hour, then add water to make 100 gallons, stir at intervals for twelve hours or so, when the stock liquor will be ready for use.

This is used to make the vat in the same way as the first above described. It is needful before adding the stock liquor in making a vat to destroy any oxygen or air which is present in the vat. This may most conveniently be done by adding thereto a solution of hydrosulphite of soda, which may be made by mixing 4-1/2 lb. zinc dust with 5 gallons of water and 3 gallons bisulphite of soda at 70° Tw., stirring well, so that the temperature does not rise too high, there is then added 2 pints caustic soda and 3 pints liquor ammonia, 20 per cent.; when all is dissolved, water is added to make up 13 gallons.

Should the vat show signs of becoming charged with indigo, indicated by its becoming of a green colour, a little of this hydrosulphite added from time to time will correct it.

The hydrosulphite-indigo vat made by either of the two methods indicated above works well, and with due care may be kept in work for months. It gives good shades of indigo, although some dyers consider that these have not the rich bronze hue got from the lime and copperas vat. The shades are rather faster to rubbing.

It has been proposed to employ the dye-stuff indophenol in conjunction with indigo, in which case the method of making the vat is with zinc, bisulphite of soda, caustic soda and ammonia as last described, only in place of using all indigo a mixture of 22 lb. indigo and 7-1/2 lb. indophenol is used. Good blue shades of considerable fastness can thus be got.

_Aniline Black._--This black is produced direct upon the cotton fibre by various processes which entail the oxidation of aniline. The chemical composition and constitution of aniline black has not yet been worked out. It is not by any means an easy colour to dye, but still with careful attention to carrying out the various operations in detail excellent results can be attained.

Aniline black is the fastest black which is known, it resists when well dyed exposure to air and light, is quite fast to washing and soaping. Its disadvantages are that there is, with some methods of working, a tendency to tender the cotton fibre, making it tear easily; secondly, on exposure to air it tends to turn green, this however only happens when the black has not been dyed properly.

At the present day it is perhaps without doubt the most used of all blacks. The methods for producing it are many and varied, the following recipes show how some of the finest aniline blacks can be dyed:--

Ungreenable black is formed when the aniline is by the action of the oxidising agents converted into a substance named nigraniline. This compound when formed will not turn green on the fibre under the influence of acids.

1. The most usual oxidising agent employed for dyeing aniline black is bichromate of soda, which salt will be found much better for all purposes than bichromate of potash. Two separate solutions are prepared: (1) 61 lb. aniline, 9 lb. hydrochloric acid and 10 gallons of water; and (2) 12 lb. bichromate of soda and 20 gallons of water. After cooling, equal quantities of these solutions are mixed and the cotton worked rapidly through the mixture, in a few minutes it assumes a bronze black. The material is then wrung out and steamed for twenty minutes at 3-1/2 lb. pressure, which process renders it jet black and also ungreenable.

2. Another aniline black: For 100 lb. cotton use 11 lb. aniline oil, 15 lb. bichromate of soda, 40 lb. hydrochloric acid and 160 gallons water or 12 lb. sulphuric acid. The dye-bath is filled with the water and the cold solution of aniline oil and a part of the hydrochloric acid in water is first added, afterwards the bichromate is dissolved in a small quantity of water, working cold at first and gradually rising to the boil.

3. Another method is the following and gives a black that is fast and ungreenable and will not rub: 10 lb. chlorate of soda, 10 lb. ammonium chloride, 10 lb. copper sulphate, 35 lb. aniline salt, 101 lb. aniline oil and 20 gallons water. The sodium chlorate and ammonium chloride are dissolved in 6-1/2 gallons and the copper sulphate separately in 5-1/2 gallons water. The aniline salt is dissolved in as little hot water as possible and neutralised with a small amount of aniline oil (10 lb.). The solution of aniline salt is first added to the bath, then the sodium chlorate and ammonium chloride, and lastly the copper sulphate, dilute the whole to 14° Tw. and then enter the goods. Next steam, then run through a solution containing 10 lb. bichromate and 5 lb. soda per 100 gallons water at 160° F., after which the goods are washed and dry steamed at 15 lb. pressure.

4. A very good black is the prussiate or steam aniline black whose cheapness should recommend it. Prepare concentrated solutions of 1-3/4 lb. aniline salt in 1 gallon water, 1-1/2 lb. ferrocyanide of potash in 3/4 gallons water and 1-1/2 lb. potassium chlorate in 1-1/2 gallons water. Mix the solutions and work in a jigger, then steam in a Mather & Platt apparatus for two minutes, then work hot in a jigger in a solution of 2 lb. bichromate per 50 gallons water, dry and finish.

Either of these methods yields a good full black; with a little experience and care perfectly uniform shades will be got.