COMPRESSIBILITY OF METALS. 211 



at 20° 9.797) were made with the finally perfected apparatus, that for 

 direct measurement without magnification. The pieces were mounted 

 as compression specimens, and their length was 16.3 cm. The mean 

 deviation from a smooth curve of the 28 readings on the extruded 

 specimen (no discards) was 0.32% of the maximum pressure effect, and 

 the maximum departure from linearity was 3.5%. The corresponding 

 figures for the casting (no discards) were 0.24% for the deviation from 

 a smooth curve and 3.07% for the maximum departure from linearity. 

 The final results are given by the formulas : 



AV 

 Extruded cylinder, At 30° tt = - 10~ 7 (35.35 - 28.0 X 10~ 5 p) p 



I 



' o 



AV 

 At 75° r- = - 10- 7 (35.94 - 28.7 X I0~ 5 p) p 

 I o 



AV 

 Cast cylinder, At 30° — = - 10~ 7 (22.02 - 9.0 X lO^p) p 



AV 



— = _ io-7 (22.11 - 9.0 X l0-*p) p. 

 y o 



At 75 



o 



These results were calculated on the assumption of equal compressi- 

 bility in all directions. One third the difference between the results 

 is a minimum measure of the difference of the linear compressibility 

 in different directions in the crystal. It is to be noticed that both 

 the pressure coefficient and the temperature coefficients are greater 

 in that direction in which the linear compressibility is the greater. 



Richards and A. W. J. have both measured the cubic compressibility, 

 that is, the mean of the linear compressibility in all directions. 

 Richards finds for the initial value of bismuth of density 9.80, 29 X 

 10~ 7 . A. W. J. find the same initial value, and the average compressi- 

 bility to 10000, corrected by my new value for iron, has dropped by 

 2.3 X 10 -7 below its initial value. It is seen that both the initial 

 value and the pressure coefficient of A. W. J. are included in the range 

 of values above. 



It should be possible to calculate the difference of the linear com- 

 pressibility in different directions from the elastic constants of bismuth, 

 but these do not seem to have been determined with sufficient accuracy. 



Tin. The material was a melting point sample from the Bureau of 

 Standards, and had the following analysis: Pb 0.007, Cu 0.003, Fe 

 0.002, Sb not detected, As and S trace, Sn (by diff.) 99.988. It was 

 investigated in the form of a simple casting, cast in graphite and 



