BRIDGMAN. — MERCURY UNDER PRESSURE. 425 



change in the weight equal in amount to the weight of the displaced 

 CS2, that is, equal to the weight of CS2 of volume equal to the change 

 of volume of the mercury. The only quantities directly concerned are 

 the discontinuity of the weights and the density of the CS2 at the point 

 of discontinuity. It is not necessary to know even the temperature 

 accurately. Any consistent device for indicating changes of tempera- 

 ture, so that the weight may he plotted as some continuous function of 

 the temperature on either side of the melting point, is all that is 

 required. 



The temperature was indicated by the resistance of a coil of fine 

 double silk covered iron wire, wound on a glass core 4 inches long and 

 placed in kerosene inside a thin- walled brass tube, which was immersed 

 directly in the CS2 in which the weighings were made. The coil was 

 not calibrated for absolute temperature, but the resistance could be 

 measured with an accuracy corresponding to changes of temperature of 

 0°.002. In addition, the temperature was read on a toluol thermome- 

 ter, graduated to 0°.l, which was also immersed in the bath. The 

 readings of the thermometer were taken only to give a check on the 

 readings of the resistance thermometer, since the thermometer readings 

 were inaccurate because of varying parallax and the necessity of remov- 

 ing the thermometer partly from the bath in making the readings. 



The cold CS2 in which the mercury was weighed was contained in a 

 cylindrical Dewar flask, 2 inches in diameter and 12 inches long. The 

 inside of this was lined with a sheet of celluloid to protect the glass 

 from being scratched, and inside this a tube of heavy copper tubing, 

 5/32 inch thick, to promote rapid equalization of the temperature. 

 The most effective equalization of temperature, however, was provided 

 by a small turbine stirrer, reaching the entire length of the flask. This 

 was run constantly between readings, but was naturally stopped while 

 a weighing was being made. The mercury was contained in a thin 

 steel shell, 9/16 inch diameter, and 4 inches long, suspended by a fine 

 iron wire (0.007 inch diameter), from the beam of a sensitive balance 

 above. The quantity of mercury used was about 140 gm. It was pos- 

 sible to weigh this to 1/4 milligram, giving an accuracy on the discon- 

 tinuity of weight on freezing, which was about 0.6 gm., of one part in 

 2000. In the respect of sensitiveness, the CS2 is probably as convenient 

 a liquid as could be found, because of the high density and very low 

 viscosity and surface tension. Provision was made for warming the 

 bath after each weighing by passing a current through a small heating 

 coil immersed in the bath. 



The experimental procedure was the natural one. The Dewar flask 

 was first filled with CS2 which had been cooled in another dish with 



