Dr. Schunck on Colouring Matters. 207 



the same liquid as this xanthine. I have however not been able to 

 prove its presence by direct experiment ; but I have succeeded in 

 ascertaining indirectly that madder does in reality contain sugar of 

 some kind by means of the following experiment. Half a hundred- 

 weight of madder was treated with boiling water for several hours. 

 The liquor, after being reduced by boiling to a convenient com- 

 pass, was mixed with some yeast, and allowed to ferment. By 

 distillation an alcoholic liquid was obtained, which, after a second 

 distillation, gave 2\\ ozs. of alcohol of sp. gr. 0'9S5, which is equi- 

 valent to 9 ozs. of absolute alcohol. It is therefore evident that 

 madder contains sugar of some kind or other. 



The precipitate produced by basic acetate of lead in the solution 

 of the brown syrup was decomposed with sulphuretted hydrogen. 

 The filtered liquid was evaporated, and left after evaporation a dark 

 brown syrup, having a strongly acid taste and reaction. The brown 

 colour was no doubt due to xanthine in its oxidized state. After 

 being repeatedly dissolved, and the solution being each time evapo- 

 rated, a dark brown powder was deposited, just as in the case of the 

 original solution : nevertheless the acid taste always remained. It 

 might be supposed that this taste was due to some vegetable acid ; 

 and indeed if any such acid, or the compound of any one with the 

 alkalies or earths, had been extracted from the madder by boiling 

 water, it would most probably have been precipitated by the basic 

 acetate of lead, and it would be in the liquid obtained by the decom- 

 position of the lead precipitate that we should have to look for any 

 such acid. Now the syrup obtained after decomposing the lead 

 precipitate and evaporating the liquid, though intensely acid, con- 

 tained no oxalic, tartaric, malic or citric acid ; neither did it show 

 the least sign of crystallization ; but the watery solution gave a cry- 

 stalline precipitate with ammonia and sulphate of magnesia ; and 

 after destroying the brown organic matter contained in it by adding 

 nitric acid and boiling, and then evaporating to drive away the 

 excess of nitric acid, it gave a yellow precipitate with nitrate of 

 silver and ammonia. I therefore infer that the acid to which the 

 sour taste of the brown syrup was owing, was phosphoric acid*. 

 The sulphuret of lead, produced by the decomposition of the lead 

 precipitate, was treated with boiling caustic potash. A dark brown 

 solution resulted, which after filtration gave with muriatic acid a 

 dark brown precipitate. This precipitate, after filtration, washing 

 and drying, cohered into masses, which were brittle and black, but 

 became brown when powdered. It was totally insoluble in boiling 

 water and alcohol. It was decomposed by dilute boiling nitric acid, 



* On one occasion, after having added nitric acid to the acid syrup and boiled, 

 I obtained on evaporation crystals of an organic acid, very similar to alizaric acid, 

 but not identical with it. It was sparingly soluble in cold water, but very soluble 

 in hot. It was volatile. The watery solution gave with acetate of lead a cry- 

 stalline precipitate soluble in boiling water, with perchloride of iron a cream- 

 coloured precipitate, with acetate of copper a green crystalline precipitate, and with 

 nitrate of silver and ammonia a white flocculent precipitate. Alizarate of lead is 

 quite insoluble in boiling water, and not in the least crystalline. 



