198 



BRIDGMAN. 



The initial compressibility of lead at 20° has been found by Richards 

 to be 22.8 X 10~ 7 , appreciably smaller than the above. A. W. J. 

 gives for the initial compressibility 21.7 X 10~ 7 . They also give a 

 value for the decrease of compressibility with pressure, but they find 

 a much smaller decrease than I do. Their decrease of instantaneous 

 compressibility over a range of 10000 kg. (using my new values for the 

 change of compressibility of iron with pressure) would be 1.2 X 10 -7 , 

 against a minimum value twice as great from the formulas above. 

 A. W. J.'s average compressibility to 10000 kg. is 21.2 X 10~ 7 against 

 21.8 above for either sample. 



Thallium. This material was prepared electrolytically by me 

 several years ago, and I have already published data for some of its 

 electrical properties. Judging by the temperature coefficient of 

 resistance, its purity is high. Since the previous work the metal has 

 been kept in a sealed glass tube. The metal was now fused under 

 KCN, the fused button was hammered to fit the extrusion block, and 

 it was extruded from a diameter of 1.2 to 0.6 cm. The final length 

 was 13 cm. This was mounted in the apparatus for direct measure- 

 ment without magnification. There was no perceptible set on the 

 first application of pressure. 



Discarding the three worst points, the average arithmetical devia- 

 tion from a smooth curve of the remaining 27 points was 0.34%, and 

 the maximum deviation from linearity was 4.0% of the maximum 

 pressure effect. The deviation from linearity is unusually large for 

 thallium, and furthermore it is not symmetrical about the mean 

 pressure, so that the results cannot be represented by a too constant 

 formula. I have therefore computed the change of volume at inter- 

 vals of 3000 kg. (in terms of the volume at 30° and atmospheric 

 pressure as unity) and give them in the following table. 



TABLE I. 



Change of Volume of Thallium under Pressure. 



