70 Royal Society : — 



contact with metallic sodium that it is possible to obtain this body 

 in the anhydrous condition. I give the numbers obtained by com- 

 bustion, side by side with the theoretical values of the two formulae : 



Carbon . 

 Hydrogen 



These numbers require no commentary. 



It is not, however, in the results of analysis that M. Cloez finds 

 the chief support of his views ; he quotes an observation which at the 

 first glance appears fatal to the diatomic notions. 



" But there is" continues M. Cloez, " a capital fact (un fait 

 capital) which completely settles the question at issue : this is the 

 vapour-density of the free base." 



This density has been found by experiment to be 1*42. 



" The theoretical density calculated for my formula, referred to 

 4 volumes, is 1*315 ; the modified formula of M. Hofmann, likewise 

 referred to 4 volumes, gives the theoretical density of 2*699. 



" These results appear to me decisive, and I do not hesitate to 

 maintain the formula of the new series of bases, of which I first 

 pointed out the formation " 



I entirely agree with M. Cloez as to the importance of the deter- 

 mination of the vapour-densities, but I certainly arrive at a very 

 different interpretation of his result. 



In repeating the experiment of this able chemist, I have arrived, 

 as might have been expected, at exactly the same number. But this 

 number refers to the hydrated base, and it is easily seen that the 

 hydrated molecule, when in the state of vapour, must occupy 8 

 volumes. In calculating the theoretical density corresponding to 

 the diatomic formula when referred to 8 volumes, we arrive at the 

 number 1*35, which coincides in fact with the number obtained by 

 experiment. 



It is obvious that under the influence of heat the hydrated base 

 splits into anhydrous base (4 volumes) and water (4 volumes), 



e 4 H 10 N 2 O 2 = C 4 H 8 N 2 +2HO, 



and that, instead of taking the vapour-density of the intact hydrated 

 molecule, M. Cloez has determined the density of a mixture of an- 

 hydrous base and water, which on cooling combined again, repro- 

 ducing the hydrated compound. And here I must recall the observa- 

 tions of several chemists, especially those of M. Bineau, of M. 

 Kekule", and of M. H. Saint- Claire Deville, each of whom has had 

 the opportunity of explaining the anomalous vapour-densities in the 

 transitory decomposition of the compounds submitted to experiment ; 

 and I would quote particularly a note by Professor Kopp*, in which 

 this distinguished physicist has treated the question of anomalous 

 vapour- densities in a general manner. 



In the case before us, there is a very simple experiment, calculated 

 * Ann. der Chem. und Pharm. cv. 390. 



