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



proving that alizarine and rubiacine result from changes in the 

 xanthine. 



When madder is mixed with cold water, stirred three or 

 four minutes, and then filtered through fine calico, a deep 

 reddish-brown liquid is obtained, tasting sweet at first and 

 then disagreeably bitter ; a drop let fall upon white calico 

 stains it a deep yellow, in the same way as a solution of pure 

 xanthine does. When the liquid is allowed to stand an hour 

 or two, it becomes gelatinous, if the solution has been strong, 

 and an orange red flocculent precipitate falls; when this is 

 filtered out, the liquor appears to have undergone a change, 

 and is much diminished in intensity of colour. It is now sweet 

 only to the taste, without a trace of the bitterness so remark- 

 able before ; and a drop applied to calico stains it only a pale 

 reddish colour, with no shade of yellow. The powder filtered 

 out has a very intense tinctorial power. The filtrate, on aci- 

 dulation with sulphuric acid, gives more precipitate of the same 

 nature, and remains a pale yellow, similar to the saturated 

 solution of rubiacine and alizarine in a dilute acid. From 

 some of the freshly-filtered solution of madder, xanthine was 

 separated in the following manner : — Subacetate of lead was 

 added to throw down all colouring matter ; the lake washed 

 and decomposed by sulphuretted hydrogen, the sulphuret 

 boiled in water several times, the mixed liquors neutralized 

 with ammonia, and a small quantity of hydrate of alumina 

 added; the mixture digested half an hour and filtered from 

 the lake of alizarine and rubiacine ; on evaporation to dryness 

 and treatment with alcohol, abundance of xanthine wasobtained 

 of the usual properties. The filtrate from the madder liquor 

 which had stood till changed, was examined in like manner 

 for xanthine, but without any being found. The red powder 

 which had separated was dissolved in alcohol, precipitated by 

 subacetate of lead, and the lake decomposed by sulphuretted 

 hydrogen. On boiling the sulphuret in water, an orange 

 liquor was obtained, from which, on cooling, flocks of rubia- 

 cine and alizarine fell : the pale orange liquor then evidently 

 contained no xanthine. The sulphuret boiled in alcohol 

 yielded abundance of alizarine and rubiacine. 



It was evident from this experiment, that in the madder 

 liquor left to spontaneous action, all the xanthine had become 

 changed into some colouring matter. To see what was the 

 nature of this change, I took some madder liquor quite freshly 

 made in the cold, and added some solution of acetate of lime, 

 which precipitates alizarine. The dark red precipitate of 

 alizarine-lime having been separated, a dark reddish-brown 

 solution remained : part of this was acidulated with hydro- 



