_Light Blue._--Dye with 1-1/2 lb. Diaminogene blue B B, 1 lb. soda and 10 lb. Glauber's salt, then diazotised and develop with beta-naphthol.
_Maroon._--Dye with 6 lb. Primuline and 20 lb. salt, diazotise and develop with blue developer A N.
_Olive Brown._--Dye with 5-1/2 lb. Diamine cutch, 3 lb. soda and 10 lb.
Glauber's salt, then diazotise and develop with fast blue developer A D.
_Gold Brown._--Dye with 1 lb. Cotton brown N, 3/4 lb. Diamine bronze G, 2 lb. soda and 10 lb. Glauber's salt, then diazotise and develop with phenylene diamine.
_Walnut Brown._--Dye with 3 lb. Diamine brown M, 3 lb. soda and 20 lb.
Glauber's salt, then diazotise and develop with beta-naphthol.
_Brown._--Dye with 1-1/2 lb. Diamine brown M, 1 lb. Diamine fast yellow B, 1 lb. cotton brown N, 1 lb. soda and 10 lb. Glauber's salt, then diazotise and develop with phenylene diamine.
_Dark Plum._--Dye with 3 lb. Diamine brown V, 1 lb. soda and 10 lb.
Glauber's salt, then diazotise and develop with beta-naphthol.
_Black Brown._--Dye with 3 lb. Diamine cutch, 3 lb. Diamine black B H, 8 lb. soda and 20 lb. Glauber's salt, then diazotised and develop with phenylene diamine.
_Blue Black._--Dye with 4-1/2 lb. Diamine black R O, 3 lb. soda and 20 lb. Glauber's salt, then diazotise and develop with beta-naphthol.
_Blue Black._--Dye with 4-1/2 lb. Diamine black R O, 3 lb. soda and 20 lb. Glauber's salt, then diazotise and develop with naphthylamine ether.
_Blue Black._--Dye with 5 lb. Diamine black B O, 3 lb. soda and 20 lb.
Glauber's salt, then diazotise and develop with beta-naphthol.
_Dark Blue._--Dye with 4 lb. Diamine black R O, 3 lb. soda and 20 lb.
Glauber's salt, then diazotise and develop with blue developer A N.
_Black._--Dye with 5 lb. Diamine black R O, 1 oz. Diamine bronze G, 3 lb. soda and 20 lb. Glauber's salt, then diazotise and develop with phenylene diamine.
The Diamine blacks are a range of very useful dye-stuffs, and by their means alone and in conjunction with the various developers as seen in the examples given above a range of useful shades of blue, navy blue, and blacks of every tone can be obtained. It may also be added that many of the direct dyes, although not diazotisable, are not altered by the process and so may be used along with diazotisable dyes for the purpose of shading them, and in that way a great range of shades can be produced, particularly by combining Primuline with other dyes.
(4) DIRECT DYEING FOLLOWED BY FIXATION WITH COUPLERS.
A further development in the application of the direct dyes has of late years been made. This is a two-bath method. The cotton is dyed with certain of the direct dyes: Primuline, Diamine jet blacks, Diazo blacks, Toluylene orange and brown, Diazo brown, Diamine nitrazol dyes, Benzo nitrol dyes, etc., in the usual way. Then a bath is prepared by diazotising paranitroaniline, benzidine, metanitraniline, dianisidine, etc., or by using the ready diazotised preparations which are now on the market, Nitrazol C, Azophor red P N, Azophor blue P N, etc., and immersing the dyed cotton in this bath. Combination takes place between the dye on the fibre and the diazo compound in this bath, and a new product is produced direct on the fibre, which being insoluble is very resistant to washing and soaping. These "coupled" shades, as they will probably come to be called, differ from those produced on the fibre by the original dye-stuff, thus the Diamine jet blacks and some of the Diazo blacks give, with paranitroaniline, browns of various shades.
In this section also may be considered the method of dyeing cotton by using the direct colours in the ordinary way, and then "topping," as it is called, with a basic dye in a fresh bath.
Practically in the "coupling process" of dyeing only diazotised paranitroaniline is used as the coupler, although other amido bases of a similar nature are available.
When paranitroaniline is used as the source for the coupling bath it is well to prepare a stock bath of diazotised paranitroaniline, which may be done in the following manner:--
=Preparation of diazotised paranitroaniline.=--Take 1 lb.
paranitroaniline, mix with 1 gallon boiling water and 1 quart hydrochloric acid, stir well, when the paranitroaniline will dissolve the solution may if necessary be assisted by a little heat. Now add 1-1/2 gallons of cold water, and set aside to cool, when the hydrochloride of paranitroaniline will separate out in the form of fine crystals; when the mixture is quite cold (it cannot be too cold) there is added 1/2 lb. sodium nitrite dissolved in 1/2 gallon cold water, stir well for fifteen to twenty minutes, by the end of which time the paranitroaniline will have become fully diazotised, cold water is added to bring up the volume of the mixture to 10 gallons. This stock bath well prepared and kept in a cool, dark place will keep good for three to four weeks. This bath contains 1 lb. of paranitroaniline in 10 gallons, and it is a good rule to allow 1/2 lb., or 5 gallons of this stock bath to each pound of dye-stuff used in dyeing the ground colour to be developed up.
To prepare the coupling bath there is taken 5 gallons of the stock bath, 1 lb. sodium acetate with sufficient water for each 1 lb. of dye that has been used.
This bath is used cold, and the cotton is worked in it for half an hour, then it is taken out, washed well and dried.
Nitrazol C is a ready prepared diazotised paranitroaniline in a powder form which keeps well if stored in a dry place. The method of using is to take 8 lb. Nitrazol C, stir into a paste with water and then add this paste to the coupling bath, together with 2 lb. soda and 3/4 lb. acetate of soda. This bath is used cold and the dyed cotton is immersed in it for half an hour, then taken out, well washed and dried.
The quantity of Nitrazol C given will suffice for all shades dyed with from 2 to 4 per cent, of dye-stuff, but when paler shades are dyed, using less than say 1/2 per cent. of dye-stuff, about 4 lb. Nitrazol C, with the soda and acetate of soda in proportionate quantities, may be used.
Azophor red P N is also a preparation of diazotised paranitroaniline in the form of a dry powder which keeps well.
To prepare the coupling bath there is taken 2 lb. of Azophor red P N, which is dissolved in water and added to the bath along with 1 lb.
acetate of soda. The dyed goods are worked in the cold bath for half an hour, then taken out, well washed and dried.
The quantities given are sufficient for shades dyed with 2 to 4 per cent. of dye-stuff; for weaker shades half the quantities may be taken.
Benzo-nitrol developer is sold in the form of a yellow paste. To use it take 5 lb., stir into a smooth paste with water, then add to the coupling bath. There is then added 3 pints of hydrochloric acid, with some stirring. Allow to stand for half an hour, add 1-1/2 lb. acetate of soda and 6-1/2 oz. soda, when the bath is ready for use. The cotton is entered and worked for half an hour, then lifted out, washed and dried.
It may be mentioned that solutions of the three couplers just named may be kept for some time without decomposition, but as soon as soda and acetate of soda are added they begin to decompose and then cannot be kept more than a few hours in a good condition. It is a good plan therefore not to add the acetate of soda until the bath is to be used.
An excess of coupler in the bath does no harm, but a deficiency may lead to poor and weak shades being developed.
The following recipes show the dyes which may be applied by this method and give some idea of the colours that can be got. Only the dye-stuffs are given. Any of the above couplers can be used with them as may be most convenient.
_Black._--Dye with 5 lb. Benzo-nitrol black B, 1 lb. soda and 20 lb.
Glauber's salt.
_Olive Green._--Dye with 6 lb. Primuline, 3 lb. Titan ingrain blue and 20 lb. salt.
_Black._--Dye with 4 lb. Dianil black C R, 2 lb. soda and 25 lb. salt.
_Dark Blue._--Dye with 2 lb. Dianil dark blue R, 1 lb. Dianil dark blue 3 R, 2 lb. soda and 25 lb. salt.
_Gold Brown._--Dye with 1 lb. Primuline, 8 oz. Dianil brown R and 20 lb.
salt.
_Chestnut._--Dye with 3 lb. Primuline, 3/4 lb. Dianil brown G O, 1 lb.
Dianil brown E, 1 lb. soda and 20 lb. salt.
_Dark Brown._--Dye with 1 lb. Dianil brown 3 G O, 3 lb. Dianil brown D, 1 lb. soda and 20 lb. salt.
_Dark Green._--Dye with 4 lb. Primuline, 1-1/2 lb. Dianil black C R, 1 lb. soda and 20 lb. salt.
_Walnut Brown._--Dye with 1 lb. Dianil brown 3 G O, 8 oz. Dianil brown R, 3 lb. Dianil brown B D, 1 lb. soda, and 20 lb. salt.
_Light Green._--Dye with 3 lb. Primuline, 8 oz. Dianil blue B, 5 oz.
Dianil dark blue R, 1 lb. soda, and 20 lb. salt.
_Orange Yellow._--Dye with 3-1/4 lb. Primuline, 1 lb. Oxydianil yellow, and 25 lb. salt.
_Olive._--Dye with 3-1/2 lb. Primuline, 8 oz. Dianil brown 3 G O, 8 oz.
Dianil blue B, 4 oz. Dianil dark blue R, 1 lb. soda, and 25 lb. salt.
_Bright Yellow._--Dye with 2 lb. Primuline, and 20 lb. salt.