BRIDGMAN. — MERCURY UNDER PRESSURE. 429 



expected that the value so obtained can do more than roughly indicate 

 the probable value, since this use of the data was not contemplated in 

 the original experiment. The information comes by observing at the 

 melting point the change in the slope of the curve plotting weights 

 against temperature. The slope is evidently connected with the 

 various thermal dilatations. 

 The exact expression is found to be 



The subscript 1 refers to the liquid and 2 to the solid. i>cs. is the 



J) 

 density of the CS2. The value -^ was taken to be 0.0014. This 



amounts to assuming the value of the dilatation of CS2 to be 0.001, 

 which is the value given at 0° by Pierre's formula. There is room for 



considerable question here, but the term into which — ^ enters is only 



10 per cent of the other term involving the dilatation of the liquid 

 mercury. 



Only the last two of the sets of weighings are available for this cal- 

 culation, the CS2 having then assumed an unvarying value for the 

 density. The dilatation of the solid calculated from these two sets 

 was 0.000165 and 0.000125, mean 0.00014. The value is extremely 

 rough, but probably as good as either the value of Dewar or Grunmach. 



These data also give a rough incidental determination of the density 

 of CS2 at -38°.85. This was found to be 1.3460. It has been 

 already mentioned that this is probably slightly in error due to the 

 presence of a slight impurity of ether, but the above value was the 

 final value, and remained constant over two days, showing that what 

 little ether there was had nearly all evaporated. The density as cal- 

 culated by the third degree formula of Isid. Pierre is 1.3647.50 The 

 formula of Pierre is intended to hold only for the range 0° to 100°. 

 The discrepancy suggests at any rate the danger of using the formula 

 by extrapolation to considerable negative temperatures. 



SUBCOOLING AND SUPERHEATING. 



All these observations on the freezing and melting of mercury under 

 pressure also show that one property which apparently holds without 



" Pierre, Ann. de Chim. et Phys. (3), 15, 325 (1845). 



