MADDER.

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wherein some sulphate of soda is previously dissolved, and boiled for abouttwenty minutes with ten times its weight of a solution of alum containing10 per cent of that salt as free as possible from iron. The liquid is filteredoff from the insoluble dregs, and cooled down to 40° or 35 0 . The red-colouredsolution can be treated either (1) by saturating cautiously with carbonate of sodaequal to from one-eighth to one-tenth of the weight of alum used, so as tocause the formation of a basic alum to remain in solution. By bringing thisfluid to a boil an insoluble subsulphate is thrown down, carrying along with it allthe colouring matter contained in the solution. This precipitate is not gela-tinous, separates readily, and is easily filtered ; it is, moreover, entirely solublein acetic acid. (2). By adding to the solution a suitable quantity of acetateof lead (78 parts of that salt for every roo of alum employed), when sulphateof lead is precipitated. The red-coloured liquid, having been filtered, isboiled, when a basic sulphate of alumina is thrown down, combined with allthe colouring matter in solution. The lake thus obtained is far deeper andmore beautiful than that prepared with carbonate of soda. Instead of maddermany of its commercial preparations can be applied for this purpose ; amongthese may be noted purpurin.

It is quite clear that the preparation of madder lakes may be conducted byvarious other processes ; for instance, the colouring matter could be dissolvedin a limited quantity of alkali, and this solution saturated with hydrate ofalumina. Hitherto the preparation of an iron lake from madder, suitable forprinting purposes, has not succeeded. En passant, we mention here thatalizarin ink is largely made in Germany ; it is, of course, washed madderwhich is used for this purpose: it is intensely black, and very valuable, inas-much as it is very fast and suitable for steel pens.

Testing of Madders, Fleur de Garance, Garancin, Extracts, &c.

We have already shown that a very large number of variable conditionsexert, in some way or other, an influence upon the richness of any given kindof madder, in colouring material and the fastness of the colours produced.Sometimes madder is purposely adulterated with substances either added toincrease the weight or with organic matters of no tinctorial value at all.Three points have to be kept in view for properly testing madder, viz.—(1), thevalue of the substance for the consumer under the conditions in which it isemployed by him—a value depending upon the utilisable quantity of tinctorialmatter present and upon the fastness and purity of the dyes produced uponthe fabrics ; (2), the absolute quantity of colouring matter present in thepowder; (3), the testing for and quantitative determination of foreign andmert substances. Since the first pointhas the greatest interest tothe consumer,it has been most studied, and we owe to M. H. Schlumberger a most practical“-and at the same time most complete—process for its proper manipulation.

M. Schlumberger’s process for estimating the utilisable tinctorial value ofany kind of madder or garancin, and the test for the fastness of the coloursproduced, may be summarised as follows :—The principle of this mode oftesting is a dyeing experiment, with a known quantity of madder and a knownsquare surface of mordanted tissue, prepared—as used on the large scale—forted, rose-colour, and pink, with alumina mordants, and for black, lilac, andpurple, with iron mordants. The result is compared with the effects produced