202 BRIDGMAN. 



There seem to be no previous determinations of the compressibility 

 of strontium. 



Lithium. This was from Merck, obtained before the war, sealed in 

 glass under oil, and was from the same lot as that used in determining 

 the effect of pressure on resistance. A chemical analysis showed 0.7% 

 Al and a trace of Fe. This was extruded cold to a diameter of 0.6 

 cm. The original piece was of square section; the extrusion produced 

 little change of section or of length, but only a change in the shape of 

 the section from square to round. The density at 20° was 0.546. 

 The final length was 6.3 cm. and it was mounted as a compression 

 specimen in the apparatus for direct measurement without magnifica- 

 tion. 



Two regular series of runs at 30° and 75° were made. The average 

 departure of the 29 observed points from a straight line (no discards) 

 was 0.15% and the mean departure from linearity was 4.9% of the 

 maximum pressure effect. The departure from linearity was about 

 15% higher at the higher temperature than at the lower, a difference 

 much beyond the limits of error. The final results are contained in 

 the formulas : 



AV 

 At 30° — = - 10- 7 (86.92 - 97.5 X l^v) V 



V 







AV 

 At 75° -p- = - 10- 7 (89.72 - 107.3 X lO^p) p. 



''o 



The initial compressibility at 20° of lithium of density 0.534 was 

 found by Richards to be 88 X 10~ 7 . This agrees with the above with- 

 in the limits of error indicated by Richards' two significant figures. 



Sodivm . This was from Eimer and Amend, obtained before the war. 

 It was not the identical lot, but was obtained at about the same time 

 and is presumably similar to the lot for which I have already deter- 

 mined the effect of pressure on the electrical conductivity and melting 

 point. No chemical analysis has been made, but the sharpness and 

 high value of the freezing point are evidence of its high purity. The 

 specimen was prepared by cutting from the interior of a large coherent 

 block of sodium a smaller piece, perfectly clean and with no inclusions 

 of any sort, and forming this by cold extrusion and pressing in a special 

 mold into a cylinder 0.9 cm. in diameter and 2.5 cm. long. Tins was 

 mounted as a compression specimen in the apparatus for direct meas- 

 urement without magnification. 



The two regular runs were made at 30° and 75°. There was no 



