Phenylene diamine is a most important developer. It comes into the market in two forms, as a powder, very nearly pure, made into a solution by dissolving 10 lb. with 20 gallons of water and 5 lb. hydrochloric acid, and as a solution prepared ready for use. Developer C (Bayer) and developer E (Bayer) are preparations of diamine, the former in a powder, the latter in a solution. Phenylene diamine can be used with the addition to the developing bath of acetic acid or soda.
Schaeffer's acid is a sulpho acid of beta-naphthol, and is dissolved by taking 10 lb. of the acid and 7½ lb. soda, boiling with 50 gallons of water. About 1¼ per cent. is required for developing full shades.
Developer B (Bayer) is ethyl beta-naphthylamine, in the form of its hydrochloric acid compound. The bath is made from 10 lb. of the developer and 50 gallons of water, 1¼ per cent. being used to obtain full shades.
Developer D (Bayer) is dioxy-naphthalene-sulpho acid, and simply requires dissolving in water to make the bath.
Toluylene diamine is a homologue of phenylene diamine and is used in precisely the same way.
Generally the special developers issued by the various colour firms simply require dissolving in water to form the developing bath.
The cotton, previously being passed through the diazo
tising bath, is then run into the developing bath, in which it is kept for from twenty to thirty minutes or until the required shade is fully developed, after which it is taken out, rinsed and dried. The method of working is the same for all the developers, and may be carried out in any kind of vessels. As is indicated above, the developing baths may be kept standing and be freshened up as required; they are used cold. Sometimes two developers are mixed together, in which case care should be taken that an alkaline developer naphthol or phenol be not mixed with an acid developer (phenylene diamine, naphthylamine, etc.), unless the acidity of the latter has been neutralised with soda; otherwise the developer might be thrown out of the bath in an insoluble and hence useless form.
The advantages of the diazotising and developing process just described may be summed as—easy and quick working, superior fastness to washing, soaping and milling, increased fastness to light and softness of the dyed fibre.
Scarlet.—Dye with 3 lb. Primuline and 20 lb. salt, at the boil for one hour, diazotise and develop with beta-naphthol.