RELATION OF ATOMS TO VOLUMES. 69 



Recent experiments performed by (Erstedt and 

 Despretz, have proved that this is actually the 

 case that the volume of sulphurous acid, cyano- 

 gen, ammonia, and sulphuretted hydrogen, dimi- 

 nishes much more rapidly under an equally 

 increasing pressure, than oxygen and nitrogen, 

 as in common air consequently, that the law of 

 Mariotte is not true when applied to gases indis- 

 criminately ; but only to such as have the same 

 degree of elastic force. Despretz regards the 

 above deviation from the law of Mariotte, as 

 referable to some unknown law which regulates 

 the constitution of gases. 



When I come to treat of the causes which 

 modify the elastic force of gases, it will be shewn 

 that their volume and compressibility are deter- 

 mined by their relations to caloric, and not by 

 the number of atoms in a given volume. 



Berzelius maintains in a recent work, entitled 

 Des Proportions Cldmiques, that all gaseous bodies 

 in the simple state, contain the same numbers of 

 atoms, or that the atomic weights of simple bodies 

 are represented by their specific gravity in the 

 gaseous state : from which it would follow, that 

 the atomic weight of hydrogen is TT that of 

 oxygen, (instead of -0, corresponding with the 

 difference between their specific gravities. And 

 as it was found that water is always composed of 

 2 volumes of hydrogen to 1 of oxygen, it was in- 

 ferred by Davy, Berzelius, Prout, and others, that 



