Dalton's Atomic Theory. 363 



formed his atomic theory. According to this theory, the mole- 

 cular weight of steam ought to be greater than the molecular 

 weight of oxygen, and this result in connexion with the hypo- 

 thesis M/S — would require the specific gravity of steam to 

 be greater than the specific gravity of oxygen. Experiments 

 gave opposite results ; they made the specific gravity of 

 oxygen greater than the specific gravity of steam. Hence, 

 one of the two — the new atomic theory or the hypothesis 

 M/S = — must be wrong. Dalton rejected the latter (Note- 

 book, i. p. 246). 



The extension of the investigation to other gases, however, 

 furnished several examples which gave nearly the same value 

 for M/S = C. Note-book, i. p. 258 (R. 41), contains a table of 

 12 gases with their specific gravities and Dalton's molecular 

 weights. I have recalculated the specific gravities on the 

 unit of hydrogen, and in place of the diameters of molecules 

 calculated by Dalton I have deemed it sufficient to give the 

 molecular volume, M/S. 



Table of the 19th Sept. 1803 (R. 41). 



Molecular Specific 



Name of the gas. Weight. Gravity. M/S. 



Hydrogen 1 TOO TOO 



Oxygen 5-66 1460 038 



Nitrogen 4'00 125 032 



Nitrous oxide 13-66 20-9 065 



Nitric oxide 966 143 067 



Carbonic oxide 10-10 130 077 



Carbonic acid 1570 195 080 



Hydrocarbon 540 8-6 063 



Ammonia 5'00 7'5 066 



Sulphurous acid 2000 29*0 0'69 



Sulphuretted hydrogen 15*40 140 1*1 



Steam 6'66 9-0 074 



The values of M/S are not equal for the different gases, but 

 may be arranged in three groups : — 



I. II. in. 



M/S. M/S. M/S. 



Nitrogen ... 0-32 Hydrocarbon 0*63 Hydrogen ... 1*0 



Oxygen 0-38 Nitrous oxide 065 Sulphuretted},, 



Ammonia 0*66 hydrogen j 



Nitric oxide 067 



Sulphurous acid 069 (S0 2 ) 



Steam 074 



Carbonic oxide 077 



Carbonic acid 0'80 (CO.) 



