SECT. in. DIFFUSION OF GASES, 1 1 5 



atmospheric air. When a portion of air confined in a 

 vessel was allowed to penetrate into a vacuum through 

 graphite or un glazed earthenware, the nitrogen passed 

 more rapidly than the oxygen in the ratio of 1'0668 to 

 1, and the portion of oxygen is proportionally increased 

 in the air left behind in the vessel. The increase of 

 oxygen actually observed when the air in the vessel was 

 reduced from 1 volume to 0*5 was 0'48 per cent. The 

 diffusion was continued till the air in the vessel was 

 reduced to 0*0625 and the concentration of the oxygen 

 in it amounted to 2*02 per cent. The molecular or 

 diffusive mobility exercises a certain influence on the 

 heating of gases by contact with heated liquid or solid 

 substances. The more rapid the molecular movement 

 of a gas is, the more frequent will be the contact of the 

 molecules and the quicker will be the communication of 

 heat. The greater cooling power of hydrogen compared 

 with that of oxygen or air is probably owing to that 

 cause. ( Oxygen and hydrogen gas have the same 

 specific heat for equal volumes ; but a hot object placed 

 in hydrogen is really touched 3-8 times more frequently 

 than it would be if placed in oxygen gas. Dalton had 

 already ascribed this peculiarity of hydrogen to the 

 high mobility of the gas.' 4 



It appears that isomorphic substances such as chlo- 

 ride, bromide, and iodide of sodium, have a similar dif- 

 fusibility, another of the many analogies between these 

 singular marine substances. 



Modern chemistry is essentially experimental ; the 

 unprecedented magnitude to which British manufac- 

 tures have risen is chiefly owing to experiments con- 

 ducted with consummate skill and dexterity. In these 

 investigations, accidental circumstances have sometimes 

 occurred which led to other researches quite different 



M. H. Kopp. 

 T2 



