850 



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 densit5^ 



The transpiration of twenty other gases and vapours is experi- 

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

 gases, with tube resistances varying in amount from 1 to 1000. This 

 list includes protocarburetted hydrogen, olefiant gas, ammonia, cya- 

 nogen, hydrocyanic acid, hydrosulphuric acid, bisulphide of carbon, 

 sulphurous acid, sulphuric acid, chlorine, bromine, hydrochloric acid, 

 ether, methyiic ether, chloride of methyl, coal-gas and the vapours of 

 water, alcohol and coal-tar naphtha. 



The principal results respecting the transpiration of these vapours, 

 and on the influence which pressure and temperature have upon the 

 transpiration of a gas, are summed up as follows : — 



The velocity of protocarburetted hydrogen is 0'8, that of hydrogen 

 being 1, 



The velocity of chlorine appears to be 1 ^ that of oxygen ; of bro- 

 mine vapour and sulphuric acid vapour the same as that of oxygen. 



Ether vapour appears to have the same velocity as hydrogen gas ; 

 their densities are as 37 to 1. 



Olefiant gas, ammonia and cyanogen appear to have equal or nearly 

 equal velocities, which approach closely to double the velocity of 

 oxygen. 



Hydrosulphuric acid gas and bisulphide of carbon vapour appear 

 to have equal or nearly equal velocities. 



The compounds of methyl appear to have a less velocity than the 

 corresponding compounds of ethyl, but to be connected by a certain 

 constant relation. 



The resistance of a capillary tube of uniform bore to the passage 

 of any gas is directly proportional to the length of the tube. 



The velocity of passage of equal volumes of air of the same tem- 

 perature, but of different densities or elasticities, is directly propor- 

 tional to the density. The denser the air, the more rapidly does it 

 pass under a constant propulsive pressure. 



Rarefaction by heat has a similar and precisely equal effect in 

 diminishing the velocity of the transpiration of equal volumes of air, 

 as the loss of density and elasticity by diminished pressure has. 



A greater resistance in the capillary is required to bring out the 

 law of densities, than appears necessary for the two preceding results ; 

 and a resistance still further increased, and the highest of all, to 

 bring out the law of temperatures. 



Finally, transpiration is generally promoted by density, and equally 

 whether the increased density be due to compression, to cold, or to 



