BRIDGMAN. — MERCURY UNDER PRESSURE. 397 



tempt to force the above very imperfect data to give more accurate 

 results. 



It may be mentioned, however, that the above results are fully as 

 consistent as the results which have been obtained by previous ob- 

 servers for the electrical resistance of solid mercury at atmospheric 

 pressure. Thus Weber ^'^ found the following values for the ratio of 

 the conductivity of the solid mercury to that of the liquid out of which 

 it is freezing : 3.2, 4.2, 3.9, 4.0, 3.5, 4.0. Taking the reciprocals so as 

 to compare with the above form, these become 0.31, 0.24, 0.26, 0.29, 

 0.25 ; different measurements of the same quantity. Cailletet and 

 Bouty 38 give the single number 0.24, while Grunmach in his first 

 paper 39 gives 0.67 and redetermines it in a later paper ^^ as 0.40. 

 The high values of Grunmach are doubtless to be explained by the for- 

 mation of cracks in the mercury when freezing. This error can hardly 

 come in the present work. In explanation of the other outstanding 

 discrepancies, the fact does not seem to have been sufficiently consid- 

 ered that mercury freezes into crystals which may have different con- 

 ductivities in different directions. It is known that the conductivity 

 of bismuth, for example, may change by 60 per cent in different direc- 

 tions, and that of iron glance by 100 per cent. It is to be expected, 

 therefore, that the particular form of vessel in which the mercury is 

 frozen, by influencing the position in which the crystals tend to sepa- 

 rate out, would have an eff"ect on the apparent change of resistance 

 on freezing. *i 



Finally, mention may be made of an unsuccessful attempt to get the 

 heat of transformation from these same resistance measurements. The 

 idea was to measure the depression of the freezing point occasioned by 

 dissolving some metallic impurity in the mercury, the commencing of 

 freezing being indicated by a kink in the curve giving resistance as a 

 function of the pressure. The depression of the freezing point gives 

 the heat of transformation by a well known formula. The difficulty 

 with the method is that there is no metal which gives a depression of 



" Weber, Wied. Ann., 25, 245-252 (1885), and 36, 587-591 (1888). 



38 Cailletet et Bouty, C. R., 100, 1188 (1885). 



39 Grunmach, Wied. Ann., 35, 704-772 (1888). 

 " Grunmach, Wied. Ann., 37, 508-515 (1889). 



*^ Since the writing of this paper Onnes (Kon. Akad. Wet. Proc., 4, 113- 

 115 (1911)) has given data from which the ratio of the resistance of solid to 

 liquid mercury may be found to be 0.237. This value was computed by the 

 author from the values given in Science Abstracts for the resistance of a given 

 quantity of mercury (172.7 ohms at 0°C., and 39.7 ohms in the solid state at 

 the melting temperature) . 



