" Specific Heat of Saturated Ether Vapour." 293 



I believe, warrant the amalgamation of this part of our dis- 

 cussion with the former, which is chiefly based on the latter 

 authors' measurements. For the pressure of 100 cm. we 

 may take 



^=0-001145, * 3 = -0-00000031, 



and as we have to deal with pressures below 200 cm., we 

 may make use of the following formula : — 



o p =/(T)-T|^j^. 



I obtained thus the following numbers : — 



1 



t. 



dT 2 " 



t d P 2 i>r , 



o 

 



00000543 



0000047 



10 



563 



51 



20 



584 



55 



30 



620 



60 



It follows then that the influence of pressure on the specific 

 heat c p is completely negligible when the temperature range 

 to be considered is from 0° to + 30° or thereabout. 



To sum up, the above examinations, or rather estimates, 

 seem to justify the first assumption that 



H = c ? , 



and also the second assumption that 



Then come the questions, What are the values of the heat 

 of vaporization v, and how does it vary with temperature ? 

 Here again Ramsay and Young's measurements were of 

 great importance to me. I found besides those the measure- 

 ments of Battelli* to be of special interest, as they cover 

 the temperature range (0° to + 40°) which we have been con- 

 sidering in particular. In the latter case the values of v were 

 to be calculated from the given data, and in doing this I took 

 no account of the specific volumes on the liquid-line which 

 are not given by Battelli; but this will be of no consequence, 



* Battelli, Ann. de Chim. et Phys. 6 e ser. tome xxv. (1892). 



