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-Lussae, Berzelius, and 

 others 1 recognised in the facts discovered by the first a 



1 Dalton was the only person who weight, and that in consequence 



doubted the correctness of Gay- great uncertainty reigned for a long 



Lussac's figures, although both time in these matters. This in- 



Thomson and Berzelius pointed out duced L. Gmelin to disregard the 



to him the great support they volumetric relations in his system 

 afforded to the atomic theory, j of equivalents, to the great detri- 



Berzelius also saw the usefulness ment of those who in the middle of 



of the law of volumes in fixing the the century were brought up with 

 smallest combining or atomic num- | very vague and unsatisfactory ex- 



bers in cases where the reference to planations on this subject differ - 



weight alone left the matter unde- ent numbers being used in books 



tided. Thus he correctly inferred on organic and inorganic chemistry, 



that the formula of water should A great confusion existed at that 



be H 2 0, as we write it to-day, be- time, Gerhardt showing good rea- 



cause two volumes of hydrogen sons, based upon his observations of 



combined with one of oxygen. But the substitution of hydrogen in or- 



it was unfortunate that, through game compounds and the system of 



his want of appreciation of Avo- classification which he introduced, 



gadro's further expositions, he was why several of Gmelin's figures 



unable to reconcile more completely should be doubled ; but the matter 



the appeal to volume with that to was not cleared up till Cannizzaro 



