LOW-TEMPERATURE RESEARCHES 



high temperatures are reached. Costly fuel must be 

 burned and the heat applied to the water before it can 

 avail to do its work. But suppose we were to place 

 our portion of liquid air, limpid and water-like, in the 

 cylinder of a locomotive, where the steam of water 

 ordinarily enters. Then, though no fuel were burned 

 though the entire engine stood embedded in the snow 

 of an arctic winter it would be but a few moments 

 before the liquid air would absorb even from this cold 

 medium heat enough to bring it above its critical tem- 

 perature ; and, its atoms now dancing apart once more 

 and re-exerting that enormous pressure, the piston of 

 the engine would be driven back and then the entire 

 cylinder burst into fragments as the gas sought exit. 

 In a word, then, a portion of liquid air has a store of 

 potential energy which can be made kinetic merely by 

 drawing upon the boundless and free supply of heat 

 which is everywhere stored in the atmosphere we 

 breathe and in every substance about us. The diffi- 

 culty is, not to find fuel with which to vaporize it, as 

 in case of water, but to keep the fuel from finding it 

 whether or no. Were liquid air in sufficient quantities 

 available, the fuel problem would cease to have any 

 significance. But of course liquid air is not indefinitely 

 available, and exactly here comes the difficulty with 

 the calculations of many enthusiasts who hail liquefied 

 gas as the motive power of the near future. For of 

 course in liquefying the air power has been applied, for 

 the moment wasted, and unless we can get out of the 

 liquid more energy than we have applied to it, there is 

 no economy of power in the transaction. Now the 

 simplest study of the conditions, with the mechanical 



VOL. V. 5 65 



