MADDER.

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obtained is submitted to hydraulic pressure, and steeped for forty-eight hoursin a weak solution of carbonate of soda, sp. gr. 1*014 = 3° Tw. The materialis again squeezed and thus freed from alkali, and the steeping is repeated witha weaker alkaline solution. The colouring matters, accompanied by someimpurities, are precipitated from the alkaline solution by an acid. This pre-cipitate having been collected on a filter, washed, pressed, and dried, isexhausted by boiling alcohol, and the filtered alcoholic solution precipitatedwith water. A similar mode of proceeding has been proposed by M.Schutzenberger, with this difference, that he applies phosphate, or preferably,pyrophosphate, of soda instead of carbonate, thus obtaining a pure colouringmatter. Good extracts of madder may be obtained by treating eithergarancin or flowers of madder with— (a) boiling acetic acid, sp.gr. 1*060,12° Tw.The hot filtered liquid deposits, on cooling, abundance of a red flocculentmatter; (*&) by means of hot glycerin, which dissolves the colouring mattersand deposits them on cooling; (c) by means of boiling benzin or rectifiedboiling sulphide of carbon, best applied under pressure with special provisionagainst explosion and ignition; (d) by means of a boiling acidulated solutionof alum, which dissolves the colouring matter, and throws it down on cooling.It is quite clear that none of these methods are commercially available in con-sequence of the expense and labour required.

We have now to mention some processes wherein water is used not to aCtupon the pre-formed colouring matter, but upon their soluble glucosidespresent in madder, which has not previously undergone any other operationthan mechanical trituration, and is not too old. Mr. Higgin treats freshlyground madder with water containing from 3 to 6 per cent of its weight ofacetate of lead and acetic acid, the lead salt being added with the view ofpreventingfermentation of the glucosides. The solution is filtered after standingfor one hour; ammonia is added to the solution, which is thereby turned red ;heat is applied, while a current of air is passed through to oxidise substancespresent, after which chloride of calcium is added for precipitation. Thematerial thrown down is collected on a filter, washed, and decomposed by anacid, when the colouring matter is separated from the lime salt. A far moregenerally applicable method is that devised by M. E. Kopp, who appliessulphurous acid in aqueous solution; this solution, made in the usual manner,should contain from 4 to 5 or 54 thousandths of sulphurous acid. If thewater is pure (relatively free from calcareous matter) there is added to thissolution about from 4 to -j^^th of hydrochloric acid, in order to saturate thesmall quantity of carbonate of lime present even in the Alsace madder. If thewater contain calcareous matter in larger quantity, more hydrochloric acid isrequired. The madder to be operated upon by this sulphurous, acid solutionshould neither be pulverised too finely nor be simply coarsely broken up. Inthe first case filtration and expression are rendered more difficult, and in thelatter the aCtion of the liquid becomes unequal, and the operation of squeezingout is rendered almost impracticable. The madder is mixed with from ten totwelve times its weight of the sulphurous acid solution, placed in wooden tubsclosed with tightly fitting covers, and left standing for from twelve to twenty-five hours, care being taken to stir the magma now and then. The semi-fluidmass is poured into a stout linen bag, and the tub rinsed out with a little cleanwater, which is added to the magma in the bag. The liquid is allowed to run