FERMENTATION OF BEER. 353 



are composed of absolutely the same elements, in 

 equal proportions ; with the single exception, that 

 alloxantin contains 1 equivalent of hydrogen more 

 than alloxan. 



When alloxantin is treated with chlorine and ni- 

 tric acid, it is converted into alloxan, into a body, 

 therefore, which is alloxantin minus 1 equivalent of 

 hydrogen. If on the other hand a stream of sulphuret- 

 ted hydrogen is conducted through alloxan, sulphur 

 is precipitated, and alloxantin produced. It may be 

 said, that in the first case hydrogen is abstracted, 

 in the other added. But it would be quite as simple 

 an explanation, if we considered them as oxides of 

 the same radical : the alloxan being regarded as a 

 combination of a body composed of C^ W ff 0^ with 

 2 equivalents of water, and alloxantin as a combina- 

 tion of 3 atoms of water, with a compound consist- 

 ing of C^ W W 0^. The conversion of alloxan into 

 alloxantin would in this case result from its eight 

 atoms of oxygen being reduced to seven, while al- 

 loxan would be formed out of alloxantin, by its com- 

 bining with an additional atom of oxygen. 



Now, oxides are known which combine with water, 

 and present the same phenomena as alloxan and al- 

 loxantin. But no compounds of hydrogen are known 

 which form hydrates ; and custom, which rejects all 

 dissimilarity until the claim to peculiarity is quite 

 proved, leads us to prefer an opinion, for which there 

 is no further foundation than that of analogy. The 

 woad (^Isatis tinctoria) and several species of the 

 Nerium contain a substance similar in many respects 

 to gluten, which is deposited as indigo blue, when 

 an aqueous infusion of the dried leaves is exposed 

 to the action of the air. Now it is very doubtful 

 whether the blue insoluble indigo is an oxide of the 

 colorless soluble indigo, or the latter a combination 

 of hydrogen with the indigo blue. Dumas has found 

 the same elements in both, except that the soluble 

 compound contained 1 equivalent of hydrogen more 

 than the blue. 



30^ 



