HYDROSTATICS. 



19 



Table for solids and liquids repre- 

 sent the absolute weight of a cubic 

 foot of each ; if we remove the deci- 

 mal point, and add a cypher where 

 there are only two decimals thus a 

 cubic foot of mercury weighs 13,580 

 ounces and a cubic foot of bar-iron 

 7,7-8 ounces. 



To ascertain, in like manner, the ab- 

 solute weight of the gases, we have 

 only to observe that 100 cubic inches 

 of common air weigh 30.50grs. ; and 

 as there are 1728 cubic inches in a 

 cubic foot, the simple method of calcu- 

 lation will stand thus: As 100 : 30.50 

 grs. : : 1728 : 527. C4 rs., the weight of 

 a cubic foot of common air. 



In order to ascertain the weight of a 



cubic foot of any other kind of gas, it 

 is nec-essary merely to observe its speci- 

 fic gravity in relation to that of com- 

 mon air; for instance, chlorine has a 

 specific gravity = 2.5 : hence a cubic foot 

 of chlorine will weigh 2.5 times as much 

 as the same bulk of common air ; thus 

 527.04 x 2.5 = 1317.60 grs. the weight 

 of a cubic foot of chlorine. 



If we wish to know the weight of a 

 cubic foot of any gas lighter than com- 

 mon air, we also compare their specific 

 gravities. Thus the specific gravity of 

 ammoniacal gas is 0.5, and that of 

 atmospheric air being = 1 ; then 1 728-J-2 

 = 864 grs. will be the weight of a cubic 

 foot of ammoniacal gas. And so on 

 for all other gaseous bodies. 



TABLE OF SPECIFIC GRAVITIES. 



