479 



The presence of oxygen is necessary for the formation of this acid. 

 If a watery solution of rubian made alkaline with soda or baryta be 

 kept out of contact with the air, no rubianic acid is produced, 

 whereas an abundance of the latter is obtained from the same solu- 

 tion on exposure to the atmosphere. The manner in which it is 

 formed from rubian may be represented by the following equation : 



The author considers this as the first known instance of a body, 

 belonging to the class of glucosides, or conjugate compounds con- 

 taining sugar, having been observed to form by a process of oxida- 

 tion. 



The author thinks it probable that this acid and the ruberythric 

 of Rochleder are identical, but the description given of the latter by 

 the discoverer is not sufficiently minute to enable him to come to a 

 decision on this point. Rochleder has moreover given a very dif- 

 ferent composition for his acid. Until the properties and composi- 

 tion of the latter have been more accurately investigated, the author 

 prefers considering the two acids as distinct. If they are identical, 

 then Rochleder has merely committed the common error of mistaking 

 a product for an educt. 



Rubidehydran and rubihydran have both properties very nearly 

 resembling those of rubian, from which they can only with difficulty 

 be distinguished. Neither of them however is capable of yielding 

 rubianic acid when treated in the same way as rubian. The com- 

 position of rubidehydran is expressed by the formula 



^56 "32 ^28 



that of rubihydran by 



C 56 H 39 36' 



The former contains therefore the elements of 2 equivs. of water less 

 the latter, the elements of 5 equivs. of water more than rubian. 

 Both substances give, when decomposed by strong acids, the same 

 products, viz. alizarine, rubiretine, verantine, rubiadine and sugar. 

 The products formed by acids are therefore the same as those pro- 

 duced from rubian by alkalies, which renders it probable that the 

 latter, when acted on by alkalies, is first converted into rubidehydran 

 or rubihydran, or both. 



Rubiadine may be obtained from rubihydran in large quantities 



