On the Theory of mixed Gases. 1 II 



to the pressure that confines the contents of the tubes ; and 

 if y be put for the spring of vapour of the same temperature 



measured by a column of mercury, we have g = — — -.; from 



which we also get c = -: the last expression afFards us 



an opportunity of comparing the preceding explanation, ar.d 

 therefore the theory itself, with facts ; for, according to the 

 experiments of Mr. Schmidt, 1000 parts of dry air, at 32 

 degrees of Fahrenheit, will expand to 1087' H parts, bv 

 being raised to 39 degrees, in contact with water; call this 

 number g; according to the same author, 1000 parts of 

 dry air at 32 degrees will expand to 1053-61 parts, bv being 

 heated to 59 degrees in a dry tube: let this number be /; 

 then g — I = 33'50: but yj or the spring of vapour at 59 

 degrees, is 507, according to Mr. Dalton ; then J'g = 551, 

 164; hence c = 16*15 inches; which expresses the height 

 of the barometer, together with the column of mercury con- 

 tained in the tube. If the temperature be stated at 93 de- 

 grees, c will amount to little more than eight inches : ik>w 

 it is highly improbable that Mr. Schmidt made his experi- 

 ments when the barometer stood at a height indicated by 

 cither of these numbers. Tliis application of the theory to 

 practice affords a presumptive evidence that the principles 

 of it are not altogether just, supposing the experiments of 

 Mr. Dalton and Mr. Schmidt to be correct; but a positive 

 proof of a want of accuracy in these principles may be ob- 

 tained by introducing a small change into the manner of 

 conducting the experiment made with moist air, This al- 

 teration consists in discarding the stopple of niercurv, and 

 substituting the simple pressure of the atmosphere in the 

 room of It; because, when this substance, which is impene- 

 trable to steam, has been removed, the redundant vapour 

 will, according to the theory, flow into the atmospiicrc, 

 ihcrebv leaving the moist air of the tube to follow the law 

 of expansion observed by dry »ir. With a view to lind 

 whether this be the case or not, I filled a bottle with run- 

 ning water of the temperature of 59 degrees, which, when 

 carefully poured out aeain, weighed 7794 grains. The bot- 

 tle. 



