The importance of Lime in Dyeing with madder.

Practical Magazine 17, 1876

(Chemistry applied to the Arts, Manufactures, &c.
Dyeing, Calico Printing, Bleaching, Tanning, and Allied Subjects.)

M.ROSENTHIEL has been studying the importance of lime in dyeing with madder and its derivatives. He shows that lime is fixed on textile fabrics at the same time as the colouring substances, and that a beautiful bright red on cotton contains alumina and lime, in the proportion of four atoms of aluminium to three of calcium. Rosenthiel experimented with a solution of bicarbonate of lime in the proportion of a gramme (15½ grs. troy) per litre (1¾ pt.). Pseudo-purpurine does not hold unless distilled water is used, and its tints are removed by soap. An addition of solution of lime weakens the dyeing bath. If the addition is so strong that a lake is formed with an atom of calcium, all the pseudo-purpurine will be lost and precipitated. Carbonic acid does not re-act on the insoluble lake. This is the reason why pseudo-purpurine is of no importance in dyeing with madder, which always requires the addition of a small quantity of carbonate of lime. Madder from Avignon contains this quantity of itself, but that of Alsace requires some to be added. On dyeing with Alsace madder — that is to say with a mixture of pseudo-purpurine, alizarine, and purpurine — in water free from lime, the pseudo-purpurine is first fixed on the mordant, then only the purpurine. The alizarine scarcely comes into consideration. The colours cannot be firm, being principally formed of pseudo-purpurine, and consequently do not resist soap, acid, and light. By the addition of chalk, on the contrary, the alizarine is first fixed on the mordant, and forms with the purpurine the true madder red, being also that obtained with Avignon madder. The pseudo-purpurine is again found under the form of an insoluble lake in the dyeing bath, and is lost for dyeing purposes, as well as a little of the purpurine and alizarine.

To supply this loss, the madder-dyeing baths are poured into basins apart, where the deposit takes place. The deposit, having been separated, is treated with boiling acid diluted with water. By this process the lakes are decomposed, and the pseudo-purpurine is brought to the condition of purpurine. The final product is garancine of spent madder, and for the most part contains purpurine. It is employed in the form of cakes, and takes the place of garancine, but is naturally of less value. With the hydrate of purpurine a beautiful red may be obtained in a direct way, without the use of a soap bath, which only increases the brightness of the colour.

The hydrate of purpurine, called orange colouring matter, is of no importance for dyeing, which is true of pseudo-purpurine also. Hence the only colouring matters of importance for dyeing are the purpurine and alizarine. It is easy with them to obtain all the shades required. Carbonate of lime is indispensable to the alizarine, which requires the quantity necessary to form alizarate of lime. A larger quantity is injurious, since a combination of two atoms of lime gives a deep violet blue colour, which, being scarcely soluble, has little dyeing power. If a small quantity of alizarine is boiled in water charged with lime, the liquid is coloured violet, and preserves this colour for several days. The purpurine treated in the same way gives a rose colour, which disappears after a few hours.

On dyeing with a mixture of alizarine and purpurine in distilled water, it is chiefly the purpurine that operates, even when the two are employed in equal quantities. If, on the contrary, the water is charged with lime, it is chiefly the alizarine that forms the red, and on the addition of chalk the red becomes more and more violet, while the purpurine is precipitated in the form of an insoluble lime lake.

Consequently there is a means of producing any shade what ever with the same mixture of alizarine and purpurine, by varying the proportions of chalk. This explains why often with the same garancine at one time a red may be obtained (with a small quantity of chalk), and at another a beautiful violet (with a larger quantity of chalk).

- Moniteur Industriel Belge, March 20, 1876.

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