1822.] in modifying the Specific Gravity of Gases. 305 



gravity of air at 60°, I'OOO, then the specific gravity of steam at 

 212° will be 0*472. Hence it appears that when water is con- 

 verted into steam, its volume is increased J 754 times. Now 

 this approaches very near to 1800 times, which was the increase 

 of bulk determined long ago by the experiments of Mr. Watt^^^^ 

 The following little table exhibits the specific gravity of 

 vapour at different temperatures both above and below 212% 

 calculated on the supposition that the specific gravity of vapour 

 increases as its elasticity. The reader, by means of the tables 

 of the elasticity of steam at different temperatures, which I have 

 inserted in vol. i. p. 61, of the sixth edition of my System of 

 Chemistry, may extend this little table as far as he thinks 

 proper. The specific gravity of common air at 60° is reckoned 

 unity. 



Temperature. Sp. gr. of aqueous vapour. 



32° 0-00314 



40 0-00413 



50 0-00590 



60 0-00824 



70 0-01134 



80 0-01440 



90 0-02140 



100 0-02880 



212 0-472 



250 0-944 



300 2-203 



343-6 3-776 



'*. I have entered into the preceding details, because the know- 

 ledge of them puts it in our power to determine the amount of the 

 error occasioned by the gas, whose specific gravity we are deter- 

 mining, containing as much vapour as can exist in it under the 

 given temperature. 



Let us suppose that we determine the specific gravity of com^ 

 mon air by weighing 50 cubic inches of it in a glass flask at the 

 temperature of 60°. And let us suppose further that this por- 

 tion of air is saturated with vapour from having been left for 

 some time in contact with water. 



At the temperature of 60°, the elasticity of vapour is 0-52 inch 

 of mercury, and its specific gravity 0-00824 ; while that of air is 

 1.-000. Now 0-52 is nearly l-58th of 30. The problem, there- 

 fore, is reduced to finding the specific gravity of a mixture of 

 57 volumes of air of the specific gravity 1, and one volume of 

 vapour of the specific gravity 0*00824. 



Let A = volume of air = 57. 



a = specific gravity of air = 1. 

 B = \^olume of vapour = 1. 

 h = specific gravity of vapour = 0*00824. 

 X = specific gravity of mixture. 

 "New Series, vol, hi. x . ^ . 



