xx DISSOCIATION 521 



served merely to throw discredit upon Avogadro's 

 hypothesis. 



Pebal's proof of the dissociation of sal-ammoniac 

 (1862). Deville's discovery of dissociation suggested a 

 simple explanation of these abnormal vapour-densities. Kopp, 

 following Cannizzaro (Nuovo Cimento, 1857, 6, 428), 

 pointed out (Liebig's Annakn, 1858, 105, 390) that the 

 vapour obtained by heating a dissociable substance might 



FIG. 56. PEBAL'S AI-PARATUS FOR PROVING THE DISSOCIATION OF 

 SAL-AMMONIAC. 



be merely a mixture of the decomposition-products, occu- 

 pying a larger volume and having a much lower density 

 than the undecomposed vapour. This explanation had 

 been suggested tentatively by Bineau in the case of am- 

 monium carbamate, but was first verified in the case of sal- 

 ammoniac, by the experiments of Pebal (Liebig's Annakn, 

 1862, 123, 199-202). 



