60 HISTORY OF CHEMISTRY. [LECTURE IV. 



as to the volume relations of the gases. He says there : 30 

 " In prosecuting my enquiries into the nature of elastic fluids, 

 I soon perceived it was necessary, if possible, to ascertain 

 whether the atoms or ultimate particles of the different gases 

 are of the same size or volume in like circumstances of tem- 

 perature and pressure. By the size or volume of an ultimate 

 particle, I mean in this place, the space it occupies in the state 

 of a pure elastic fluid ; in this sense the bulk of the particle 

 signifies the bulk of the supposed impenetrable nucleus, to- 

 gether with that of its surrounding repulsive atmosphere of 

 heat. At the time I formed the theory of mixed gases, I had 

 a confused idea, as many have, I suppose, at this time, that the 

 particles of elastic fluids are all of the same size ; that a given 

 volume of oxygenous gas contains just as many particles as the 

 same volume of hydrogenous." He afterwards became of a 

 different opinion, to which he was led by the following con- 

 siderations : One atom of nitric oxide consists of one atom of 

 nitrogen and one of oxygen. If, now, there were the same 

 number of atoms in equal volumes, one volume of nitric oxide 

 should be formed by the combination of one volume of nitro- 

 gen with one of oxygen, but, according to Henry's experiments, 

 about two volumes are produced ; hence nitric oxide could 

 only contain half as many atoms in the same space as nitrogen 

 or oxygen. 31 



Dalton, in his reply, refers to these considerations, and then, 

 with regard to Gay-Lussac's " hypothesis that all elastic fluids 

 combine in equal measures, or in measures that have some 

 simple relation one to another," he proceeds : 32 " In fact, his. 

 notion of measures is analogous to mine of atoms ; and if it 

 could be proved that all elastic fluids have the same number 

 of atoms in the same volume, or numbers that are as i, 2, 3, 

 etc., the two hypotheses would be the same, except that mine 

 is universal, and his applies only to elastic fluids. Gay-Lussac 

 could not but see that a similar hypothesis had been entertained 

 by me, and abandoned as untenable." 



30 New System. I, 187-188; A.C.R. 4, 6, 7. 31 Compare New 



System. I, 70-71 ; A.C.R. 4, 5. New System. 2, 556 ; A.C.R. 4, 25. 



