1 9 1 Dr. Schunck on the Constitution of 



of carbon is never obtained in the analysis of a pure crystallized 

 substance. I have subjected alizarine in various states of purity 

 so repeatedly to analysis, that I may be allowed to express a 

 decided opinion on the question of its composition. Now I 

 maintain without any hesitation, that the purer the alizarine the 

 more nearly will its composition correspond to my formula, and 

 that only in an impure state does its composition approach that 

 ascribed to it by M. Laurent. The impurity which usually 

 accompanies alizarine consists of verantine. An admixture of 

 the latter, even in considerable quantity, does not deprive aliza- 

 rine of its crystalline form ; it merely imparts to the crystals a 

 red colour, and causes it to become more or less soluble in alum 

 liquor. It is only with great difficulty that alizarine can be de- 

 prived of the last trace of verantine accompanying it. The for- 

 mula of verantine being C 14 H 5 5 , it will be seen that, in any 

 mixture of this substance and alizarine, the quantity of carbon 

 and hydrogen must be lower than in pure alizarine with the 

 formula C 14 H 5 O 4 . No specimen of alizarine can be considered 

 as absolutely pure which contains less than 69 per cent, of car- 

 bon and less than 4 per cent, of hydrogen. 

 M. Laurent objects to the equation — 



C 56 H 34 O 30 + 9H o = 2C 12 H 12 O 12 + C 32 H 19 O 15 , 

 or 



A=2B + C-9Aq, 



whereby I explain the formation of rubianine and sugar from 

 rubian, as being without any analogy in science. Nevertheless, 

 he accepts without hesitation M. Strecker's view of the decom- 

 position of tannic acid into gallic acid and sugar, which is repre- 

 sented by the equation — 



C 40 H i8 O 26 + 6HO = C 12 H 12 O 12 + 4C 7 H 8 O 5 , 

 or 



A=B + 4C-6Aq, 



an equation which does not differ very widely in its form from 

 the one just given. And surely no assumption which I have 

 made can be so extravagant as some of M. Laurent's; as, for 

 instance, when he supposes rubiacate of potash to contain half 

 an equivalent of potash, a view which is and always will remain 

 without any analogy. 



It is remarkable, that of the whole series of bodies, the only 

 one whose formula M. Laurent does not change is that which 

 is the most indeterminate in its nature, viz. the sugar. Now 

 instead of being the centre or fixed point of the system, this 

 body is the unknown quantity, whose value can only be deter- 

 mined when that of all the others has been discovered. In itself 



