on the Atomic Theory. 125 



aqueous vapour, bearing the remaining portion of the pressure = 

 0.516 of an inch ; 100 cubic inches of such oxygen weigh 33.88 x 

 0.9828 ss 33.3047 + 0.3278 vapour. The sum 33.6325 is there- 

 fore the weight of 100 cubic inches of oxygen standing over 

 water at 60°, barom. 30. Its specific gravity, compared to moist 

 air, or their relative weights, when taken by the same balloon 



33 6325 



and balance at the same time, will be . = 1.10986. But 



30.3032 



Dr. Thomson's wonder-working balance afforded him directly, in 

 these circumstances, the specific gravity 1.1117, being Dr. Prout's 

 theoretic number, where that number ought not to be found. 

 Such a fictitious, or we might rather say, factitious coincidence 

 destroys all confidence in Dr. Thomson's experiments on the spe- 

 cific gravity of the gases. 



The above calculation may be represented by the following 

 formula, calling S, the specific gravity of dry gas, (bar. 30, and 

 therm. 60°) ; v, that of vapour at 60°;/, its elastic force ; then 

 the specific gravity of the gas standing over water, bar. and 



30 — / ' -4- v 

 therm, as above, will be S X ^—- 



03 



We have seen that a volume of such moist gas consists of a 



volume of dry gas, supporting — ! of the atmospheric pres- 

 sure -f a volume of vapour supporting — ! of that pressure. 



Hence, by deducting from the specific gravity of the moist gases 

 the weight of the volume of vapour present, or its specific gra- 

 vity 0.01075, the remainder will be the specific gravity of the 

 dry gases, under a barometric pressure of 29.484 inches. Thus 

 the following tabular view arises. Specific gravity of 



Dry at 30 Bar. Dry at 29.484 B. Vapour at 60*. Moist air at 60*. 



Air . 1.00000 0.98280 + 0.01075 = 0.99355 



Chlorine 2.50000 2.457 + 0.01075 = 2.46775 



Oxygen 1.11111 1.09199 + 0.01075 tea 1.10274 



Hydrogen 0.06944 0.06825 + 0.01075 tec 0.07900 



If moist air be called unity, then the specific gravities of the 

 other gases standing over water will be 



Chlorine . . . 2.48370 



Oxygen . . . 1.10986 



Hydrogen . . . 0.7951 



In moist oxygen gas, the aqueous vapour fonns only T ^ of the 

 total weight ; but in moist hydrogen, it constitutes more than \. 



Many readers will probably complain of the prolixity of this de- 

 velopement of the influence of moisture on the specific gravity of 



