4 Ramsay, The Newly Discovered Elements. 



as the volume of the gas that occupied by 2 grams of 

 hydrogen, 28 grams of nitrogen, 32 grams of oxygen, and 

 so on — numbers proportional to the molecular weights of 

 their molecules — namely 22,222 cubic centimetres ; and if 

 we raise the temperature of that volume of gas from 0° to 

 i°C, the energy gained by the gas, measured in ergs and 

 deduced from the increase of its pressure, is 123,765,000. 

 Knowing from the researches of Joule, and of his successors 

 Rowland and Griffiths, that the value of the mechanical 

 equivalent of heat is 42,750 gram-centimetres, and dividing 

 the ergs by this number, and by the gravitation constant, 

 981, we arrive at the number of calories equivalent to the 

 energy imparted to the gas. The result is very nearly 

 3 calories, or, in other words, as much heat as will raise 

 one gram of water through 3°C must be imparted to a 

 " gram-molecule " of a gas in order to raise its temperature 

 through I'^C. 



Suppose such a gas, thus raised in temperature through 

 1°, to be allowed to expand against atmospheric pressure, 

 until its pressure falls to the original value which it had 

 before it was heated, its temperature will fall, owing to the 

 work which it does in " raising the atmosphere." In order 

 to restore it to the temperature i^C, more heat must be 

 added. The amount of this necessary heat is easily 

 calculated from the known weight of the atmosphere on 

 each square centimetre, and the distance through which 

 it is raised ; it is 2 calories, approximately. The first 

 amount of heat — that required to heat the gas at constant 

 volume — is thus 3 calories ; the second, required to raise 

 the temperature of the gas under constant pressure, when 

 it is allowed to expand, is 3 + 2 = 5 calories. The ratio 

 between these two quantities is 3: 5, or i : i"66. 



It must be remembered that the assumption involved 

 in these considerations is that tl^e molecules of gases are 



