64)2 Royal Society. 



numerical constants. As the results, too, were entirely novel, and 

 wholly unprovided for in the received view of the gaseous constitu- 

 tion, of which indeed they prove the incompleteness, it was the more 

 necessary to verify every fact with the greatest care. 



The most general and simple of the results is, that the transpira- 

 tion velocity of hydrogen gas is exactly double that of nitrogen gas. 

 These gases, it will be remembered, have a less simple relation in 

 density, namely 1 to l^. This was the conclusion respecting the 

 transpiration of these gases of his former paper, and he has obtained 

 since much new evidence in its favour. The transpirability of car* 

 bonic oxide, like the specific gravity of that gas, appears also to be 

 identical with that of nitrogen. 



The result which may be placed next in point oif accuracy and 

 importance is, that the transpiration velocity of oxygen is related to 

 that of nitrogen in the inverse ratio of the densities of these gases, 

 that is, as 14 to 16. In equal times it is not equal volumes but equal 

 weights of these two gases that are transpired, the more heavy gas 

 being more slowly transpired in proportion to its greater density. 

 Mixtures of oxygen and nitrogen have the mean velocity of these 

 two gases, and hence the time of air is also found to be proportional 

 to its density when compared with the time of oxygen. 



The relation between nitrogen and oxygen is equally precise as 

 that between nitrogen and hydrogen. The densities calculated from 

 the atomic weights of oxygen and nitrogen, namely, 16 and 14, 

 being 1 for oxygen, 0"9010 for air and 0*8750 for nitrogen, the ob- 

 served times of' transpiration of equal volumes of the same gases are 

 for oxygen 1, air 0-8970 to 0*9010, and for nitrogen to 0*8708. The 

 result for carbonic acid, which is perhaps next in interest, appears ' 

 ^t first anomalous. It is, that the transpiration time of this gas is 

 inversely proportional to its density : when compared with oxygen or 

 0*7272, the time of oxygen being 1, their velocities will of course be 

 directly as their densities. It is to be remembered, however, that 

 carbonic acid is a compound gas, containing an equal volume of 

 oxygen. The second constituent, carbon, which increases the weight 

 of the gas, appears to give additional velocity to the oxygen in the 

 same manner and to the same extent as inc» eased density from pres- 

 sure or from cold increases the transpiration velocity of pure oxygen 

 itself. A result of this kind shows at once the important chemical 

 bearing of gaseous transpirability, and claims for it a place with the 

 doctrines of gaseous densities and combining volumes. The circum- 

 stance that the transpiration time of hydrogen is one-half of that of 

 nitrogen, indicates that the relations of transpirability are even more 

 simple in their expression than the relations of density among gases. 

 In support of the same assertion may be adduced the additional fact, 

 that binoxide of nitrogen, although differing in density, has the same 

 transpiration time as nitrogen. Protoxide of nitrogen and carbonic 

 acid have one transpiration time; so have nitrogen and carbonic 

 oxide, as each pair has a common density. 



The transpiration of twenty other gases and vapours is experi- 

 mentally determined, and shown to be uniform, like the preceding 



