138 M. Stasis New Determination of the Atomic Weights. 

 their formulae only differ by nC 2 H 2 , 



C io H 4 N 4 4 C 14 H 8 N 4 4 C 16 H 10 N 4 O 4 



Xanthine. Theobromine. Caffeine. 



Strecker has indeed shown that theobromine may be converted 

 into caffeine, to which it bears the same relation as aniline to 

 methylaniline. When theobromine is dissolved in ammonia, and 

 nitrate of silver added, a precipitate forms which readily dissolves 

 in warm ammonia. On boiling this, a granular crystalline pre- 

 cipitate is deposited, which is theobromine-silver. When this is 

 treated with iodide of methyle, iodide of silver is formed, and a 

 crystalline body, which is caffeine : 



C 14 H7AgN 4 4 + C 2 H 3 I = C 16 H 10 N 4 4 + AgI. 



Theobromine-silver. Iodide of Caffeine, 

 methyle, 



Strecker attempted a similar transformation of xanthine into 

 theobromine by treating the silver compound of xanthine, which 

 contains 2 equivs. of silver, C 10 H 2 Ag 2 N 2 O 4 , with 2 equivs. of 

 iodide of methyle. He obtained a body of the same composition 

 as theobromine, but which is simply isomeric, and not identical 

 with it. 



Gerhardt had already pointed out that cholestrophane, a pro- 

 duct of the decomposition of caffeine, might be regarded as a bi- 

 methylated parabanic acid; and from this point of view Hlasiwetz 

 endeavoured, but without success, to convert parabanic acid into 

 this body. Strecker, by treating parabanate of silver with iodide 

 of methyle, has succeeded in effecting the change ; that is, by 

 replacing 2 equivs. of hydrogen in parabanic acid by 2 equivs. of 

 methyle, cholestrophane is obtained, as is indicated in the for- 

 mula 



c 4 o-n c 4 o 4 i 



c 2 o 2 ^n 2 c 2 o 2 yw 



H a J 2C 2 H 3 J 



Parabanic acid. Cholestrophane. 



Hence, while the oxidation of uric acid, of guanine, and of xan- 

 thine gives parabanic acid, from caffeine, dimethylparabanic acid 

 is obtained ; and from creatine, methylparabauic acid. 



Stas* has published the results of an investigation of the 

 atomic weights of the elements which has occupied him during 

 several years. His object was to subject Prout's hypothesis, that 

 all the atomic weights of the elements are multiples by whole 

 numbers of that of hydrogen as unity, to a more rigorous scru- 

 tiny, and to ascertain whether there was in fact a common divi- 



* Bulletin de I'Academie Roy ale de Belgique, se'r. 2. vol. x. No. 8. Lie- 

 big's Annalen, Supplement, May 1861. 



