EESEAECHES ON EVAPORATION AND DTSSOCIATION. 305 



and wfitor. Comparative I'esiilts — i.e. boilinf^-points and 

 volatilizing-points for water and ice at ideiitioal pressures — 

 were obtained between 0° and - B°. Tables are also given 

 of tlio volatilizing-points of ice, down to - I(;°, and these 

 results, when compared with those which James Thomson 

 obtained by recalculation of Regnault's data, are found to 

 give differences of vapour-pressure of ice and water greater 

 than his. But when the observed pressures for ice for 

 temperatures below 0° were compared with the pressures 

 calculated from a theoretical formula of Thomson's, it was 

 found that the observed results agreed more nearly with 

 those so calculated than with Regnault's results. 



Fischer {Wied. Ami,., 188(!, p. 4(X)) has also ]:)ublishod data 

 for water and for benzene obtained by the statical method. 

 His results with water agree very closely with ours ; but, 

 he states that with benzene the vapour-pressure of the solid 

 is not identical with that of the liquid at the melting-point. 

 In a recent paper (FUl. Mag., 1887, p. (11) wo have pointed 

 out that Fischer made use of the formula, p = a + ht + c1^", 

 which is not well adapted to represent the relations of tem- 

 perature and pressure, in preference to the one suggested 

 by Biot, h<j p = a + ha'{ + cfi'), which is better adapted for 

 the purpose. Moreover Fischer did not make use of his 

 experimental results at low temperatures in calculating the 

 constants for his formula; if these errors be rectified, his 

 results confirm the thermo-dynamical conclusion. We took 

 this opportunity of redetermining the vapour-pressures of 

 benzene, and for the liquid we obtained results identical 

 with Fischer's ; but for the solid somewhat higher tempera- 

 tures were found for tlie same pressures ; and we give 

 reasons why we regard our results as more probable, based 

 on experimental determinations of the heats of vaporization 

 of solid and li(iuid benzene, on the heat of fusion of solid 



