1884.J 



on Liquefied Gases. 



149 



filled with fluid oxygen (for projection) holds at least 1-5 cubic 

 centim. With such a quantity of fluid oxygen it is easy to show its 

 ebullition at ordinary pressures, and by means of a thermo-junction 

 to demonstrate the great reduction of temperature which is attendant 

 on its change of state at atmospheric pressure. 



Provided a supply of liquid ethylene can be had, there is no 

 difficulty in repeating all the experiments of the Eussian observers ; 

 but as this gas is troublesome to make in quantity, and cannot be 

 bought like carbonic acid or nitrous oxide, such experiments neces- 

 sitate a considerable sacrifice of time. It was therefore with con- 

 siderable satisfaction that I observed the production of liquid oxygen 



by the use of solid carbonic acid, or preferably liquid nitrous oxide. 

 When these substances are employed and the pressure is reduced to 

 about 25 mm., the temperature of —115° 0, may be taken as that of 

 the carbonic acid, and — 125° C. as that of the nitrous oxide. As the 

 critical point of oxygen, according to the Eussian observers, is about 

 — 113° C., both these cooling agents may be said to lower the tempera- 

 ture sufficiently to produce liquid oxygen, provided a pressiu'e of the 

 gas above the critical pressure, which is 50 atmospheres, is at 

 command. In any case, however, the temperature is near that of the 

 critical point ; and as it is difficult to maintain the pressure below 

 about an inch of mercury, the temperature is apt to be rather above 



