292 Mr. J. Higgin on the Colouring Matters of Madder. 



become rubiacine and part of this alizarine, the remainder of 

 the time being occupied in completing the change ; the ali- 

 zarine, being removed from solution as fast as formed, has 

 probably some influence in accelerating the change of rubia- 

 cine. This will be the final action ; and when the mordants 

 are saturated, there will always be a small residue of rubiacine, 

 which has a tendency to dull the shades ; and hence the su- 

 perior brightness of those dyed with garancine, which contains 

 no rubiacine. Examination of the residual dye liquor gene- 

 rally shows a small quantity of rubiacine, which gives it an 

 opaline appearance ; there is also always alizarine united to 

 woody fibre and lime. Examination of the dyed cloth, of 

 whatever colour, gives only alizarine, as was proved by 

 Schunck. 



It is found advantageous sometimes to mix a lower quality 

 of madder with a superior; the effect produced not being a 

 mean of those resulting separately, but not much inferior to 

 that produced by the superior madder alone. The low qua- 

 lity abounding in xanthine, has probably more than can be 

 readily converted in the required time; but as we have seen 

 that good madder can readily convert more than its own 

 quantity, the change goes on nearly as uniformly as if good 

 madder alone were used. 



The fermentation and improvement of madder, when kept 

 in the cask, is readily explained by supposing the xanthine 

 gradually to change into alizarine: this is particularly noticed 

 in Dutch madders, which abound in xanthine. Many sub- 

 stances and salts, added to a madder dyeing, weaken its in- 

 fluence very much. An examination of the residual liquor 

 uniformly shows the xanthine remaining unchanged, and the 

 dyed effect has only been produced by the quantity of alizarine 

 originally in the madder. 



Madder contains a varying quantity of sugar of an un- 

 crystallizable species, which may be isolated in the following 

 manner: — To the madder solution left after throwing down 

 xanthine, in the proximate analysis before-mentioned, is added 

 sufficient dilute sulphuric acid to throw down any lead that 

 may be in excess, then evaporated to dryness, the sugar dis- 

 solved in alcohol, decolorized by animal charcoal, and again 

 evaporated to dryness: if the evaporation be too fast, the re- 

 sulting sugar is coloured slightly; but if a gentle water-bath 

 heat has been used, it is quite colourless. 



I do not think the resins found by Dr. Schunck are ori- 

 ginally contained in madder, but have been formed during 

 the boiling. I have never in my experiments on the products 

 obtained at a low temperature, or brief boiling temperature, 



