LECTURE IV.] HISTORY OF CHEMISTRY. 63 



are present in ammonia, etc., and he thus arrives at results 

 quite different from those of Dalton. 



He points this out explicitly in his paper, and draws 

 attention to the fact that in his determinations, he starts from 

 legitimate physical principles, whereas Dalton's rules contained 

 arbitrary assumptions. He lays stress on the fact that Dalton, 

 in case he wishes to identify the physical with the chemical 

 atoms (molecules int'egr antes and elementaires\ will be forced to 

 assume that in those combinations which take place without 

 contraction, the composite atoms must be further removed 

 from one another than the uncombined ones. 



Avogadro is able, from their densities, to determine directly 

 the molecular weights of the elements known in the gaseous 

 state. This, however, is not sufficient for him, and he also 

 attempts the determination in the cases of other elements. 

 Here, however, he has recourse to more or less doubtful 

 hypotheses. He finds the atomic weight of carbon to be 11.3, 

 and that of sulphur 31.3, referred to that of hydrogen assumed 

 = i ; that is, he finds numbers which very nearly agree with 

 those adopted at present. I shall not enter into the more 

 minute details of this most interesting paper, and shall only 

 remark further that Avogadro admits the possibility of molecules 

 of elements consisting of 4, 8, etc., atoms, and believes that 

 nature has, in this very way, equalised the difference between 

 simple and compound substances. 



Starting from similar views, Ampere writes a paper on the 

 same subject three years later (i8i4). 34 His conclusions are, 

 however, less simple, as he tries to explain at the same time 

 the crystalline form of substances, by the position of the atoms 

 in the molecule. 



These speculations met, on the whole, with but little 

 attention in the chemical world. It seems as if a distinction 

 between atom and molecule was not regarded as justifiable, 

 and accordingly neither Avogadro's nor Ampere's ideas exercised 

 any immediate influence upon the science. This may also be 



a4 Ann. Chim. 90, 43. 



