438 PROCEEDINGS OF THE AMERICAN ACADEMY. 



by compression as was the temperature of the liquid in the piezometer. 

 There was, of course, some loss due to the heat capacity of the 

 piezometer. 



To calculate the heat of compression, we made use of the well- 

 known formula,^ 



42350 Cj, 



where e is the coefficient of expansion at constant pressure ; T is the 

 absolute temperature of the liquid ; A Hs the change in the tempera- 

 ture of the liquid due to an adiabatic compression of one atmosphere ; 

 and Cp is the specific heat of the liquid at constant pressure. The 

 values of Cp for different temperatures for both ether and alcohol were 

 calculated from the equations given by Regnault,^ 



q = 0.529^ + 0.000296^^ for ether, 



q = 0.5475^ + 0.00112^== + 0.0000022U' for alcohol, 



where t is temperature of the liquid on the ordinary centigrade scale, 

 and q is the amount of heat in calories required to raise the tempera- 

 ture of the liquid from 0°C. to t°C. 



In order, however, to make sure that the method of adiabatic com- 

 pression would give trustworthy results, the compressibility of alcohol 

 was determined at 20°C. by the first method, — -i. e. by waiting for the 

 heat of compression to equalize before the change of volume was read. 

 The compressibility of the same specimen of alcohol was then deter- 

 mined by the second method, in which the change of volume is read 

 rapidly and corrected for the error due to the heat of compression. 

 Ether was examined in a similar way. The values obtained by the 

 first method differing from those obtained by the second method by 

 only one per cent, the method of adiabatic compression was regarded 

 as justified, and was used in all subsequent work on compressibility. 



After the piezometer had been filled and had been in the thermostat 

 long enough to assume a constant temperature, observations were made 

 in the way just indicated, on the apparent change of volume of the 

 liquid in glass. The change of volume produced by a change of pres- 

 sure of 15 cm. of mercury was very small. In such a case, the total 

 movement of the liquid meniscus in the capillary tube amounted to 

 about 0.08 cm., and it was difficult to observe this change of volume 



8 Sir William Thomson, Mathematical and Physical Papers, 3, 238. 



9 Mem. de I'Acad., 26, 262 (1862). 



