v THE STUDY OF GASES 67 



The identification of inflammable air and fixed air 

 by Cavendish. To Cavendish belongs the credit of intro- 

 ducing the method of identifying gases by careful measure- 

 ments of their physical properties. For this purpose he 

 measured the density of inflammable air and of fixed air 

 from various sources ; in the case of fixed air the solubility 

 in water was also found. The densities were measured by 

 filling a bladder with the gas, and finding the change in 

 weight when the bladder was emptied. If the gas was 

 heavier than ordinary air the bladder became lighter when 

 emptied, but if the gas was lighter than air a gain in weight 

 was observed. In either case the density of the gas was 

 calculated from the known weight of the bladder-full of 

 air, and the change of weight on emptying the bladder. 



In the case of inflammable air a gain of weight was 

 observed amounting in four experiments to 4of, 40 J, 41 J 

 and 41 grains, when using 80 ounce-measures of gas pre- 

 pared by the action of zinc on vitriolic acid and on spirit 

 of salt, of iron on oil of vitriol, and of tin on spirit of salt 

 respectively. The gas produced by the four methods was 

 therefore the same ; as air was 800 times lighter than water, 

 80 ounce-measures of common air weighed 80 x 480 l -=- 800 = 

 48 grains ; the same volume of inflammable air weighed 

 48 - 41 = 7 grains ; this gas was therefore 48 + 7 = 6-9 times 

 lighter than common air or 80 x 480 -r 7 = 5490 times lighter 

 than water. 2 



In the case of fixed air there was a loss in weight of 

 34 grains on a volume of 100 ounces ; the air weighed 

 i oo x 480 -v- 800 = 60 grains ; the fixed air weighed 60 4- 34 = 

 94 grains ; it was therefore i T 5 (/o times heavier than air or 

 511 times lighter than water. 2 The values for fixed air 

 were trustworthy; those for inflammable air were un- 



1 480 grains = I ounce. 



2 The correct values are : for inflammable air, 14*4 and 11600 ; for 

 fixed air, I '53 and 530. 



F 2 



