[Illustration: FIG. 27.--Dye-tub for Paranitroaniline Red.]
The beta-naphthol bath does not keep well and in time tends to grow brown, and when this occurs stains are invariably produced on the cotton. When the yarn or cloth has been prepared with the beta-naphthol, and dried, the developing should be immediately proceeded with, for it is found that by allowing the prepared cotton to lie about it becomes covered with brown stains, and when such stained cotton is passed through the developing bath stains and defective dyeing result.
It has been found that by adding a little tartar emetic to the beta-naphthol bath this is largely if not entirely prevented, and the prepared cloth may be kept for a reasonable length of time before proceeding with the development without fear of stains being formed.
Various additions have been made from time to time to the naphthol bath.
Some of these take the form of special preparations of the colour manufacturers, and are sold as naphthol D, naphthol X, red developer C, etc., sometimes gum tragacanth has been added, at others in place of Turkey-red oil there is used a soap made from castor oil with soda and ammonia, but such complicated baths do not yield any better results than the simple preparing liquor given above.
[Illustration: FIG. 28.--Padding Machine for Paranitroaniline Red.]
=Dyeing Paranitroaniline Red on Piece Goods.=
The dyeing of this red on to piece goods only differs from that on yarn by reason of the difference in the form of material that is dealt with.
1. _Preparing or Grounding._--The same liquor may be used. This operation is best done on a padding machine, a sketch of which is given in Fig. 26, showing the course of the cloth through the liquor. This is contained in the box of the machine, and this is kept full by a constant stream flowing in from a store vat placed beside the machine. After going through the liquor, the cloth passes between a pair of squeezing rollers which squeeze out the surplus liquor. Fig. 28 shows a view of a padding machine adapted for grounding paranitroaniline reds. After the padding, the cloth is dried by being sent over a set of drying cylinders, or through what is known as the hot flue.
2. _The Developing._--After being dried, the pieces are sent through a padding machine charged with the developing liquor made as described above, after which the cloth is rinsed, then soaped, and then washed.
Some dyers use a continuous machine for these operations, such as shown in Fig. 29.
While the developing bath used for piece goods may be the same as that used for yarns, some dyers prefer to use one made somewhat differently, thus 6-1/4 lb. paranitroaniline are mixed with 7 gallons boiling-water and 1-1/2 gallons hydrochloric acid; when dissolved 16 gallons of cold water are added, then, after completely cooling, 3-1/2 lb. sodium nitrite dissolved in 3 gallons cold water. After twenty minutes, when the diazotisation is complete, water is added to make the whole up to 40 gallons. The acetate liquor is made from 13-1/4 lb. acetate of soda in 13-1/2 gallons of water.
Equal quantities of these two liquors are used in making the developing bath.
[Illustration: FIG. 29--Developing Machine for Paranitroaniline Red.]
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.
[Illustration: FIG. 30.--Indigo Dye-vat for Cloth.]
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.