Anthracen, tr. and ed. by W. Crookes

To prepare red steam colours with purpurin for goods mordanted with alumina, the following method is recommended:-Add to the purpurin 20 per cent. of its weight of soda, mix well, and add hot soft water. A splendid red colour is thus obtained, which is filtered, and allowed to cool a little. It is then mixed with starch-paste, so that the consistence may be fit for printing. The colour keeps for a long time without spoiling. After printing, the goods are steamed and washed. Twenty grms. of purpurin per litre yield a very full red. If, on filtering the solution of purpurin, any colouring-matter remains on the filter, it may be used in ordinary dyeing operations.

In dyeing wool with purpurin, we mordant as for garancin, either with tartar and alum or tartar and tin solution. The tin solution, which gives the best results, is—

which is added gradually, the dissolving-pan being set in cold water. This solution is used after filtration.

To mordant the wool, it is entered in the beck at 30°, and raised in the course of an hour to 70° C. It is then taken out, wrung, and dyed in purpurin, entering at 30° C., and raising to a boil in halfan-hour.

The purpurin may be advantageously neutralised with a little soda or crystalline carbonate of ammonia. For this purpose it is put in a bottle, with a sufficient quantity of boiling water, and the alkaline carbonate is added. The whole is then poured into the dye-beck.

Wool mordanted with alum and tartar takes a very bright crimson. If mordanted with tartar and tin solution, it is dyed almost as fine a red as with cochineal, 2 to 4 grms. sufficing for a square metre of muslin or merino. To obtain a very bright orange-red, the wool is prepared with tartar and tin solution, to which a little young fustic or extract of fustic has been added. The whole is heated to 70° C. in a tin dye-pan, lifted, rinsed in flowing water, and dyed with purpurin as above. If the tone is not sufficiently orange, a little extract of young fustic may be added to the dye-beck.

Wool mordanted with alum is printed with purpurin in the same manner as cotton.

Purpurin can be fixed upon silk in the following manner :—The silk is mordanted with acetate of alumina, at 5° B., and dried or

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prepared with precipitated alum, obtained by adding hydrate of alumina to common alum. Filter the solution when cold, and set it at 7° B. by the addition of water. The handkerchiefs are passed twice through this mordant, and dried at a steam heat. The next day they are passed through water at 50° C. In mordanting silk with acetate of alumina, a little chalk is added to the water. Dry at once, and stiffen with a little gum Senegal, or preferably tragacanth, at 2–5 grms. per litre.

The goods are then printed with the following colour :-32 grms. of purpurin, finely ground, are mixed with 1 litre of water, and 12 grms. soda-crystals are added. The purpurin dissolves perfectly in a few minutes, and the solution is strained through calico.

It is thickened with 200 grms. pale calcined starch, and the whole is then boiled. Print when the colour is cold, and steam with pressure when dry. Wash and soap in a weak clear soap-beck, at 40°-50° C., or even hotter. Half a gramme or a gramme of tannin may be added to the colour, dissolved in water holding 1 grm. of soda-crystals in solution.

Purpurin yields reds as deep as can be required, if the above-stated proportions between the colouring-matter and the soda are increased. All slightly alkaline salts may serve to dissolve purpurin. Borax or basic borate of soda is preferable, and dissolves rather more than sodacrystals; then follow the bicarbonates of soda and ammonia, carbonate of ammonia, potash, &c. Silicate of soda cannot be used, as under certain circumstances it yields gelatinous precipitates.

Purpurin, in dyeing mordanted silks, differs remarkably from madder or garancin. Its high tinctorial power admits of a very extended application, as the dye-becks can be perfectly exhausted.

Purpurin can also be employed in the form of aluminous lakes, red or rose. For this purpose either of the two following methods

may be adopted :—

1. The solubility of purpurin in boiling salts of alumina is utilised; a solution of alum or other aluminous salt is heated, and purpurin is added, previously well ground up with water. The solution is allowed to cool down, and when luke-warm, a little chalk or soda is added, to hasten the precipitation of the lake.

2. The purpurin is dissolved in water containing a very little soda, and this solution is poured into that of an aluminous salt. The aluminous lake is formed immediately.