426 



.SCIENTIFIC THOUGHT. 



according to definite proportions of their weight, it follows 

 that in the gaseous state these combining weights of bodies 

 have either equal volumes or such as stand in very simple 

 proportions. Now the amount of matter (measured by 

 weight) in the same volume is called the density of a gas. 

 It therefore follows, by putting Dalton's and Gay-Lussac's 

 discoveries together, that the combining weights of gases 

 are either directly proportional to their densities or to a 

 simple multiple thereof. Some years after this discovery 

 in 1809, Gay-Lussac extended his statement so as not 

 only to embrace elementary gases, such as hydrogen, 

 oxygen, and nitrogen, but also compounds, such as am- 

 monia, carbonic acid, hydrochloric acid, and showed how, 

 if they enter into chemical combination, they likewise do 

 so in the simple proportions of one volume of one, to one 

 or two volumes of the other. 



Whilst chemists such as Gay-Lussac, Berzelius, and 

 others ^ recognised in the facts discovered by the first a 



^ Dalton was the only person who 

 doubted the correctness of Gay- 

 Lussac's figures, although both 

 Thomson and Berzelius pointed out 

 to him tlie great support they 

 afforded to the atomic theory. 

 Berzelius also saw the usefulness 

 of the law of volumes in fixing the 

 smallest combining or atomic uum- 

 beis in cases where the reference to 

 weight alone left the matter unde- 

 cided. Thus he correctly inferred 

 that the formula of water should 

 be HoO, as we write it to-day, be- 

 cause two volumes of hj'drogen 

 combined with one of oxygen. But 

 it was unfortunate that, through 

 his want of appreciation of Avo- 

 gadro's further expositions, he was 

 unable to reconcile more completelj' 

 the appeal to volume with that to 



weight, and that in consequence 

 great uncei'tainty reigned for a long 

 time in these matters. This in- 

 duced L. Gmelin to disregard the 

 volumetric relations in his system 

 of equivalents, to the great detri- 

 ment of those who in the middle of 

 the century were brought up with 

 very vague and unsatisfactorj' ex- 

 planations on this subject differ- 

 ent numbers being used in books 

 on organic and inorganic chemistry. 

 A great confusion existed at that 

 time. Gerhardt showing good rea- 

 sons, based upon his observations of 

 the substitution of hydrogen in or- 

 ganic compounds and the system of 

 classification which he introduced, 

 why several of Gmelin's figures 

 should be doubled ; but the matter 

 was not cleared up till Cannizzaro 



