LOW-TEMPERATURE RESEARCHES 



is often several inches in thickness, giving a very char- 

 acteristic and unmistakable appearance. 



Another commercial use to which refrigerator ma- 

 chines are now put is in the manufacture of various 

 drugs, where absolute purity is desirable. As different 

 substances congeal at different temperatures, but the 

 same substances at uniform pressure always at the 

 same temperature, a means is afforded of freeing a 

 drug from impurities by freezing, where sometimes the 

 same result cannot be accomplished with like thorough- 

 ness by any other practicable means. Indeed, by 

 this means impurities have been detected where not 

 previously suspected. And Professor Ramsay has de- 

 tected some new elementary substances even, as con- 

 stituents of the air, which had previously not been 

 dissociated from the nitrogen with which they are 

 usually mixed. 



Such applications of the refrigerator principles as 

 these, however, though of vast commercial importance, 

 are held by many enthusiasts to be but a bagatelle 

 compared with other uses to which liquefied gases may 

 some time be put. Their expectations are based upon 

 the enormous potentialities that are demonstrably 

 stored in even a tiny portion of, say, liquefied air. 

 These are, indeed, truly appalling. Consider, for ex- 

 ample, a portion of air at a temperature above its 

 critical point, to which, as in Thilorier's experiments, 

 a pressure of thirty-one tons to the square inch of the 

 encompassing wall is being applied. Recall that ac- 

 tion and reaction are equal, and it is apparent that the 

 gas itself is pushing back struggling against being 

 compressed, if you will with an equal power. Suppose 



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