CLEARING MADDER STYLES.

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previously possessed. That this effect is really caused by the soap is provedby the fact, that if the dyed fabrics, on being taken from the dye-beck, after awincing in cold water for the removal of adhering particles of dye-stuff, wereimmediately placed in a bath of nitro-muriate of tin, the colours would be farmore attacked than is the case in the ordinary process of clearing. By thetreatment with the tin preparation, instead of which very dilute nitric acidmay be used, a remarkable effect is produced. While undergoing this treat-ment the reds and pinks seem almost destroyed, becoming orange, but by thesubsequent soap bath the fine shades are brought out very vividly, exhibitingalso a peculiar “bloom,” which before the application of the tin-salt bath wasnot seen at all. The intensity of the colour is, however, slightly diminished,but this effect is taken into consideration during the dyeing process, care beingtaken to procure rather too deep a colour.

The experiments of Schlumberger have proved that the acid of the tin bathtakes away a small portion of the alumina, while also some of the oxide oftin becomes fixed, the acid, moreover, removing the last portions of yellowmatter. M. Persoz has thought that the tin bath might perhaps have apeculiar effect upon the principal colouring matter by entirely altering it,but this view is certainly not well founded, since more recent experiencehas proved that pure alizarin may be extracted from dyed fabrics which havebeen submitted to the clearing operations. It is far more likely that theeffect of the nitro-muriate of tin is the complete elimination of the purpurin,pseudopurpurin, and the yellow colouring matters. The two former sub-stances yield with aluminous mordants a red, less bloomy, bright, and vivid tintthan is produced by alizarin, and therefore the peculiar effects of the tin bathare readily accounted for. To this should be added, that the fixing of someoxide of tin instead of the eliminated portion of alumina plays an importantpart. The second soap bath also, at nearly boiling heat, does not simply actas detergent, but it is probable that again some of the fatty acid is fixed. Asregards the action of the last boiling under pressure, it is very difficult to ex-plain precisely what it effects. According to M. Persoz, the effect is the fixingof a larger quantity of fatty matter, and there is good reason to adoptthis as a correct view. It is supported by the following facts:—Redmadder-dyed cloth, which has either not been cleared at all or only incom-pletely so, turns, on being treated with acids, an orange-red, and, on beingnext immersed in milk of lime, becomes bluish ; but after a complete processof clearing, and especially after the boiling under pressure, as described, thecloth stands the action of these agents without thereby undergoing any per-ceptible change ; the effect, therefore, produced by the said boiling is some-what analogous to the well-known properties of the so-called Turkey-red,which, as we shall presently see, owes its great power of resistance to thepresence of a modified fatty substance in combination with the aluminouslake. The clearing of the purples, puce browns, and blacks, where no red ispresent on the cloth, requires, for bringing out all the beauty of these coloursln the highest degree of perfection, the agency of chlorine or of bleaching-powder. Without doubt the main action of the hypochlorites of lime, of soda,an d magnesia, as industrially applied, is oxidising. It is very probable thatthe iron mordants undergo in the dye-beck a partial reduction, and that theproper degree of oxidation required is restored by the application of the hypo-