EXPERIMENTAL KNOWLEDGE OF THE PROPERTIES OF MATTER. 127" 



comparable with each other ; and the suggestion imposes itself upon one 

 that this may be au expression — very approximately true — of a general 

 law with regard to vapour-pressures and temperatures applicable to any 

 volatilisable liquid — to any at least which can be lieated with no chemical 

 change, or none but dissociation ; in other words, that bodies of this 

 kind in the liquid state are, in spite of their apparently great divergencies 

 in respect of relations of vapour-pressure to temperature, really very 

 similarly constituted in that respect if compared under physical condi- 

 tions, which this formula of Ramsay and Young in some way represents, 

 at least approximately. 



Application of the formula to Liquid Oxygen. 



The case of oxygen is of such interest that it is impossible to leave- 

 this important paper without treating of it. 



Olszewski ' published a series of determinations by a hydrogen-ther- 

 mometer of temperatures of liquid oxygen, and vapour-pressures corre- 

 sponding, the temperatures varying from the critical temperature of 

 oxygen — 118'8° C. to — 211'5° C. ; and critical pressure being 50'8 atmos =: 

 38,608 mm., and the pressure for the lower temperature being 9 mm. 

 Olszewski was unable to measure any lower temperature, because at this 

 point so much liquid oxygen had evaporated that the bulb of the ther- 

 mometer was not sufficiently covered with it. 



Taking water to compare with, c was found = — •0008932. By inter- 

 polation from Olszewski's numbers, temperatures were determined for 

 vapour-pressures 800, 1000, 1500, 2000, and so on up to 20,000 mm.; 

 the critical temperature corresponding to a critical pressure 38,600 mm. 

 of oxygen vapour being about 154° in ahsohite temperature. 



The calculated and the interpolated values of absolute temperature of 

 oxygen are as under : — 



The same comparison of absolute temperatures is made for oxygen 

 and alcohol, the vapour-pressures of alcohol and corresponding tempera- 

 tures being known over a large range ^ up to 155° C. by air thermometer, 

 at which temperature the vapour-pressure is 8259-19 mm. The tempera- 

 tures calculated by the formula, from the table for alcohol, give absolute 

 temperatures nearly agreeing with those got from Olszewski's observed 

 values by interpolation. 



Again, a third calculation of vapour-pressures and temperatures was 

 made from the data given by Regnault for sidphur^ where air-thermo- 

 meter temperatures centigrade are given at intervals of 10° from 390° 



' Compt. Rend. 100, p. 350. J.C.S. 1885, May Abs. p. 476. 

 - Regnault in Memoires, t. xxvi. p. 375. 

 ' Ibid. p. 530. 



