BRIDGMAN. — WATER UNDER PRESSURE. 475 



sure, and the gasolene itself gave evidence of considerable viscosity at 

 the lower temperatures. Attempt was made to use a still lighter oil 

 to avoid altogether this viscosity. Pentane was tried, but after a 

 number of failures had to be abandoned. There is evidently some ac- 

 tion under pressure between the pentane and either the water or the 

 ice. The action seems to be one of solution. In every case water 

 found its way sooner or later through the long connecting tube to the 

 manganin resistance coil, where it short-circuited the coil, making 

 measurements impossible. 



The nickel steel cylinder containing the water was supported from 

 above by means of the connecting pipe in a cylindrical Dewar flask, 

 2 inches diameter and 10 inches long. The low temperature was ob- 

 tained with solid COa and ether, or usually CO2 and gasolene, this being 

 much cheaper and giving nearly as low a temperature as the ether. 

 No thermostatic regulation was used with the apparatus. The thermal 

 insulation provided by the bath proved sufficient so that the slight 

 amount of regulation necessary could be performed from time to time 

 by hand, by dropping in small masses of solid CO2. The bath liquid 

 was stirred by blowing bubbles of air into it through a tube reach- 

 ing to the bottom of the flask. It was possible with very little effort 

 to keep the temperature constant to 1/2°, which was sufficient for 

 most requirements, since in the region of these experiments the equi- 

 librium pressure is affected only slightly by changes in temperature. 

 Greater constancy of temperature was attained by the exercise of a 

 little more care when this was necessary. 



Temperature was measured with a nickel resistance thermometer. 

 This was a coil of bare nickel wire wound in spiral grooves on a hard 

 rubber cylinder, which was immersed in kerosene in a thin, tightly 

 fitting tube of glass. The top of this tube was carefully stoppered 

 to prevent the condensation of moisture around the leads. The 

 glass tube, 3/8 inch o. d., was immersed directly in the temperature 

 bath. The response to changes of temperature was always very 

 prompt. The resistance of this wire was measured on the same bridge 

 wire of the same Carey Foster bridge as that on which the measure- 

 ments of the resistance of the manganin coil for pressure were made. 

 Either the nickel or the manganin resistance, with the appropriate 

 extension coils, could be connected with the bridge wire by two double- 

 throw mercury switches in paraffin blocks. The temperature was ordi- 

 narily read both before and after the readings of pressure and piston 

 displacement. The coil was calibrated by comparison at 0°, —50°, and 

 —80° with a nickel resistance thermometer of Leeds and Northrup, 

 which had been calibrated at the Bureau of Standards. The sensitive- 



