1521.] Causes of Calorific Capacity, Latent Heat, fyc. 453 



Cor. 3. — Because when the vapour is all condensed, and the 



water beneath 1172-6, true temp, t = — %—. " — , we obtain 



* o (tc + to ) 



«/ ss , _ , ; that is, a quantity of water being given, a 



quantity of vapour may be found, whose temperature is known, 

 which, condensed on the water, shall raise its temperature from 

 any one given temperature to any other under 1172-6, or the term 

 of ebullition, according to the pressure under which we operate. 

 Cor. 4. — And since by the same formula we get w — w 



-p — - — -, we are enabled to determine the quantity of water, 



which, at a given temperature, shall condense with a given 

 increase of temperature a given quantity of steam whose temper- 

 ature is known. 



If we put t = 1172-6, the theorem w = — ll7 ~ , '' w' 



determines the quantity of water at a given temperature which it 

 will just require to condense the whole of a given portion of steam 

 at a given temperature. 



Cor. 5. — By the second theorem in Cor. 2, we find w = 



— T_ ' '" . Therefore the quantity and temperature of the 



steam being given, the quantity of water at a given temperature 

 may be found, which, introduced into the apparatus, shall be 

 wholly converted into steam, and the temperature of the mixture 

 be reduced to a given temperature. 



Scholium. 



The numbers 6 and 11, that I have found for the proportion 

 of the baromerins of water and vapour, will also, like those for 

 water and ice, give the ratio of the relative powers of equal 

 weights of water and vapour at 212° Fahr. to effect changes in 

 the temperature of any other body ; or, in the language of the 

 old doctrine, they exhibit the ratio of the " calorific capacities." 

 Therefore if the capacity of water be 1, that of vapour must be 

 y = 1*83, which differs from the experimental determination 

 1*55 of Dr. Crawford by a quantity which every philosopher will 

 allow to be much within the limits that probability would assign 

 to the errors of experiment. 



From the baromerin of vapour thus determined, we might 

 easily deduce that of any gas whatever, supposing the vapour and 

 gas respectively homogeneous. For this purpose, the theorem I 

 published in the Annals for July, 1816, is serviceable. By that 

 theorem, it appears that the baromerins in any homogeneous 

 airs are reciprocally proportional to the square roots of the spe- 

 cific gravities ; and hence the baromerin of water being unity, 

 that of any homogeneous gas (taking for granted that vapour 



