422 PROCEEDINGS OF THE AMERICAN AC/VDEMY. 



for the liquid is probably open to greater question. The error intro- 

 duced by this cannot be very large, however, because of the small 

 temperature range over which the solid cooled. By far the greatest 

 possibility of error seems to be in the simple measurement of tempera- 

 ture. The thermometry of low temperatures must have been in a 

 chaotic state at the time, judging by the values given by Person for 

 known fixed temperatures. He gives the value on the air thermometer 

 of the melting point of mercury as —41°. This point is now known to 

 be — 08°. 85. He furthermore states that his alcohol thermometer read 

 higher than a mercury thermometer at — 20°. No statement what- 

 ever is made as to the corrections applied to the readings of this alco- 

 hol thermometer. If, however, he did apply the correction of the 

 mercury thermometer to the alcohol thermometer, then there is still 

 the possibility of great variation between — 20° and — 40°. The con- 

 sistent behavior of three calibrated alcohol thermometers which have 

 been used in this present work indicates a possibility of error of as 

 much as 3 per cent between — 20° and — 40°. 



Person made three determinations of the latent heat, giving 2.77, 

 2.86, and 2.83, mean 2.82, as against 2.735 found above. The use of 

 this latter value seems to be justified, therefore, in preference to that 

 of Person. 



Person's value for the latent heat has entered directly into the 

 determination by Regnault ** in 1849 of the specific heat of solid 

 mercury. Again the value of Regnault is apparently the only value 

 which we have of this quantity. The method of Regnault was exactly 

 the same as that of Person, except that the mercury was initially at 

 — 77°.7, so that the heat given out by the solid in cooling to the melt- 

 ing point was a very appreciable part of the total heat given out. In- 

 cidentally Kegnault's temperature measurement was very probably at 

 fault as well as Person's, for he gives — 40° as the melting point of 

 mercury. Regnault made two determinations of the mean specific 

 heat from — 77°.7 to the melting point, giving 0.0314 and 0.325. 

 Evidently the effect of a smaller latent heat of melting would be to 

 give a larger specific heat to the solid. Substituting the value found 

 above produces a change of 6.5 per cent in the values given by lleg- 

 nault, giving 0.0334 and 0.0346 respectively, mean 0.0340. 



The data used in determining the change of volume may also be 

 used to give evidence on one point for which they were not intended. 

 The slope of the curve plotting piston displacement against pressure is 

 evidently going to be dilferent above and below the melting point be- 



** Regnault, Ami. de Chim. et Phys., 26, 268-278 (18i9). 



