86 CHEMICAL DISCOVERY AND INVENTION 



pressures combined with cold, the pressure being limited by the 

 capacity of the thick glass tubes to resist it. The cold was the 

 temperature of the carbonic acid and ether mixture which, 

 under reduction of pressure, would go down to -160 F. 



Atmospheric air was compressed to ^-yyth of its volume, in 

 which state its density was little inferior to that of water, oxygen 

 to -err th, hydrogen to ^^th, an d so on, but in no case was there 

 any appearance of liquefaction. But observations on the com- 

 pression of carbon dioxide at different temperatures led to the 

 discovery that when the gas contained in a tube is partly liquefied 

 by pressure alone, on gradually raising the temperature to 31 C. 

 (88 F.), " the surface of demarcation between the liquid and 

 gas became fainter, lost its curvature, and at last disappeared. 

 The space was then occupied by a homogeneous fluid which 

 exhibited, when the pressure was suddenly diminished or the 

 temperature slightly lowered, a peculiar appearance of moving 

 or flickering strise throughout its entire mass. At temperatures 

 above 88 F. no apparent liquefaction of carbonic acid or 

 separation into two distinct forms of matter could be effected, 

 even when a pressure of 300 or 400 atmospheres was applied. 

 Nitrous oxide gave analogous results." 



A series of comparisons were then made by Dr. Andrews on 

 the volume of carbon dioxide and air when submitted to in- 

 creasing pressures at different degrees of temperature. When his 

 results were plotted, the volumes against the pressures, a series 



FIG. 41. CARBONIC ACID CURVES. 



