230 Scientific Intelligence. [Sept. 



sure of atmospheric air; and/ = pressure or tension of vapour in any 

 moist gas. Then the following formul.-t will be found useful in calcu- 

 lating the volumes, weights, and specific gravities, of dry and moist 

 gases ; putting M for the volume of moist gas ; D for that of dry gas ; 

 and V for that of vapour, all of the same pressure and temperature. 

 i. M = D + V. 



.i« P-f 



S. ^ M a V. 



p -f f 



" If we wish to infer the specific gravity of any dry gas from the 

 observed specific gravity or weight of the same mixed with vapour, it 

 will be convenient to expound p by that particular value which corre- 

 sponds with rt, namely 30 inches ot mercury ; and let s = the specific 

 gravity of the dry gas, and vo = the observed weight of 100 cubic 

 inches of the moist gas. 



Then we shall have the following, viz. 



30 f f 



5. -30^ . 5 a + ^ X -620 a = tu. 



6.5 = =^ (to --^ X -620 fl.) 

 30 -/a V P ' 



Exemplifications. 



1. 98 vol. dry air + 2 vol. vapour = 100 vol. of moist air. 



2. Given p = 30,/= -5, and M = 100. 



Then^-^ . M = D, the dry air, = 98^. 

 p 



3. And- M = V, the vapour, = If. 



4. Given D = 100, p = 30,/= •4<. 



SO X 100 



Then ^^^ = 101*35, the moist air. 

 Given V* = 2,;? = 30,/= -3. 



SO X 2 

 Then —^ = 200, the moist air. 



5. Let/= -5, s = Mil, a = 30-5, p = 295, 



Then ^^^ Mil x 30-5 + 2^ X -62 x 30-5=: 33-64 = tv, which 



gives the specific gravity 1'103. 



6. Let/ a, and p as above, and tv = 2*5, corresponding to specific 

 gravity 0-8197. 



Then. = ,-^^^3 (2-5 - ^ x '62 X 30-5) = -07266. 



" The above formulae apply equally well if V be a permanent gas, or 

 any other vapour beside that of water, the specific gravity of the gas or 

 vapour being substituted instead of -620 that of steam." 



♦ It is easy to see that V, in this and the other cases, mostly will denote a virtual vo- 

 lume only ; or such as would result, if the vapour w^r? condensible lilje a gas, wHhou^ 

 ^g convertible into a lic^uid. 



