BRIDGMAN. — MERCURY UNDER PRESSURE. 379 



It is to be noticed, however, that Richards' value involves directly his 

 own value for the compressibility of iron, which is almost certainly 

 much too low. If the more probable value O.OeSS is used instead of 

 Richards' value O.OeSS, the value of Richards for mercury becomes 

 O.O539I at room temperature. The change of compressibility with 

 pressure found by Richards is higher than that found above, dropping 

 from 3.80 between and 100 kgm. to 3.60 between 500 and 600 kgm. 

 As mentioned in a previous paper, this is probably due to error in the 

 pressure gauge. Carnazzi ^9 has published data over a much wider 

 pressure and temperature range than the other previous observers, up 

 to 3000 kgm., and from 23° to 192°, but with less pretense to accur- 

 acy, as only two figures are given in the results. Carnazzi gives O.O537 

 as the initial compressibility at 23°. Since Carnazzi's results are the 

 only ones which give the change of compressibility with pressure over 

 an at all wide pressure range, it may be permitted to anticipate a little 

 in order to compare his results with the present ones. Carnazzi finds 

 a drop in the compressibility of 0.064 from 250 kgm, to 2750 kgm. at 

 23°, against 0.0625 of the present work. His change in the mean 

 dilatation between 23° and 53° is from 181 at pressure to 157 at 3000, 

 against a change in the mean dilatation between 0° and 22° from 181 

 to 163 for the same pressures as found in the present work. 



Finally, the results may be compared with the results of the previous 

 paper. *o It has been already stated that the method of the paper was 

 open to question, but it should be remembered, as was stated at the 

 time, that the primary object of that work was to find whether the 

 compressibility of mercury showed any marked change over a pressure 

 range from to 6000, and that the data were obtained because of their 

 bearing on another question. The accuracy was sufficient for the pur- 

 pose in hand, and the employment of the method seems to have been 

 justified in view of the very much greater speed and ease of manipula- 

 tion. The initial compressibility at 20°, making correction as already 

 explained for the erroneous value used for the compressibility of steel, 

 was O.O5375. 



Taken altogether, the agreement with the more accurate of the pre- 

 vious determinations is as satisfactory as could be expected : 380 at 

 0° against 379 of Amagat and 374 of de Metz, and 395 at 22° against 

 394 of de Metz and 391 of Richards. 



^' Carnazzi, loc. cit. 

 ^^ Bridgman, loc. cit. 



