212 Dr. Schunck on Rubian and Us Products of Decomposition, 



This specimen of sugar had therefore the same composition 

 as that obtained by the action of erythrozym on rubian*. 



The analysis of the acid, its compounds and products of de- 

 composition just detailed, lead to the conclusion that its compo- 

 sition must be expressed by the formula C** H^ 0% and that it 

 belongs to the class of the so-called glucosides, the copula con- 

 tained in it being alizarine. Its decomposition, by means of 

 strong acids and alkalies, into alizarine and sugar, is symbolized 

 by the following equation : — 



C62H«027 + 5HO = 2C^4H504-f2C^2H»20^2. 



In order to remove all doubt concerning the true formula of this 

 substance, I determined the quantities of alizarine which were 

 obtained by decomposition of weighed quantities of the acid with 

 sulphuric acid and with caustic soda. 



1-7210 grm. rubianic acid, dried at 100° C, gave, when de- 

 composed with sulphuric acid, 0'7310grm. dry alizarine =42*47 

 per cent. 



1-2020 grm. rubianic acid yielded, when decomposed with 

 pure caustic soda, on precipitation with sulphuric acid, 0*5430 

 grm. alizarine=45-17 percent. 



Assuming the formula C^^ H^^ 0^ to be correct, 100 parts of 

 acid should, according to theory, afford 43*44 of dry alizarine. 

 If Strecker^s formula for alizarine, C^® H^ 0^, were the correct 

 one, then the only possible formula for rubianic acid, though the 

 calculated composition would then not agree very well with that 

 found in my experiments, would be C^^ W^ 0^, in which case 

 the quantity of alizarine derived from 100 parts of acid would 

 be 62' 70. It will be seen, therefore, that the view which I 

 have adopted of the constitution of the acid derives considerable 

 support from these determinations. 



A comparison of the composition of rubian and rubianic acid 

 shows that the latter can only be derived from the former by 

 means of oxidation. In order however to remove all doubt on 

 this point, I made the following experiment. A solution of 

 rubian was divided into two equal parts. One half was boiled 

 to expel all the air it might contain, then mixed with a certain 

 quantity of caustic soda, and immediately put into a bottle, 

 which the liquid just sufficed to fill, and which was then closed 



* Phil. Mag. for June 1853, p. 424. 



