INDIGO.

487

process does not appear to have been ever extensively carried out: the inten-tion was that it should be applied in combination with madder, the mordant forthe latter being printed on at the same time.

A pra&ical printer of great experience informs us that, setting aside the veryserious difficulty of steaming the goods before they are dry, whereby they areexposed to many and serious accidents, the patentee’s process, as publishedin his specification, would have to be greatly modified before it could be prac-tically applied.

M. E. Schlumberger has thoroughly investigated the subjed of fixing indigoby the so-called steaming process. He tried the following method:—Startingwith the knowledge that hydrated protoxide of tin reduces indigotin in thecold,’provided an alkali be present, he found that if, instead of the alkali,cyanide of potassium be employed, the indigotin becomes only soluble (and ofcourse first reduced) during the steaming. The following mixture was tried :—

Indigo-paste (that is to say, indigo ground to pulp with) p arts

water), containing 20 per cent dry indigo .i

Best cyanide of potassium (in cakes). 16 ,,

Wet pasty hydrate of protoxide of tin. 16 „

Gum-water.52 ,,

This colour was found too expensive, and had the disadvantage of runningtoo readily, and could not be printed on simultaneously with any coloursgiving off acids. It was never M. Schlumberger’s intention to introduce thiscolour on the large scale, but he found that it is capable of producing a mostmagnificent fast green on being combined with cadmium yellow, preparedaccording to M. Sacc, by means of a hyposulphite. This green resists, with-out alteration, all the operations of madder dyeing.

When indigo-dyed calico is treated with a strong solution of caustic alkali,the shades of colour become deeper, in consequence of the contradtion thetissue undergoes.

Indigo-dyed fabrics are recognised by their exhibiting a somewhat dull bluecolour, which resists the adtion of alkalies and of all acids which do not—byadting as oxidising substances—destroy the colour. Among these acids thenitric and chromic are the more common. Chlorine-water destroys the bluecolour of indigo. A freshly-made solution of zinc in sulphurous acid alsodecolourises indigo.

When vatted tissue is immersed in a hot alkaline solution of protoxide oftin it becomes decolourised, and the liquid turns blue on exposure to air.When a vatted tissue is treated with the strongest fuming sulphuric acid thefibre is destroyed, but if the liquid be diluted with water and filtered a blueliquid will be obtained, exhibiting all the charadteristics of the so-calledSaxon blue.

We have now to turn our attention to the application of the sulphuric deri-vatives of indigo. Sulphindigotic and sulphopurpuric acids have no affinitywhatever for vegetable fibres, not even after they have been animalised oralbuminised. When even the so-called Saxon blue is occasionally applied tocotton, after the excess of sulphuric acid has been saturated with eitheracetate of lead or acetate of soda, whereby an equivalent proportion of aceticactd is set free, and a preparation formed which is erroneously called acetate