COMPRESSIBILITY OF METALS. 201 



Calcium from Professor Bidwell, 



AV 



At 30° -=r = - 10- 7 (56.97 - 47.2 X 10" 5 p) p 

 "o 



AV 

 At 75° — = - 10- 7 (58.50 - 52.7 X 10- 5 p )p. 

 v o 



The higher temperature coefficient of the second and purer sample 

 is to be noticed ; the pressure coefficient of the two samples is about 

 the same. 



The initial compressibility of calcium of density 1.54 has been found 

 by Richards to be 56 X 10 -7 . This agrees with the value above 

 within the limits of error indicated by Richards' two significant 

 figures. 



Strontium. This material was from the same lot most kindly sup- 

 plied me by Dr. B. L. Glascock as that for which I have previously 

 determined the changes of resistance under pressure. 14 The purity 

 is unusually high. The most homogeneous lump of this lot was 

 chosen, and it was extruded in two stages to a final diameter of 0.3 cm. 

 and machined to a length of 1.1 cm. The extrusion was performed at 

 a temperature of 270° and under oil to avoid chemical action. The 

 sample was mounted as a compression specimen in the lever apparatus 

 for long specimens. 



One preliminary run was made, in which it was not possible to reach 

 more than 10,000 kg. because of trouble with the pressure apparatus, 

 and then two regular runs to 12,000 at 30° and 75°. Within the limits 

 of error the results of the first incomplete run agreed with the final 

 results. The average departure of the 28 observed points of the 

 regular runs from a smooth curve (no discards) was 0.35% and the 

 maximum deviation from linearity was 3.9% of the maximum pres- 

 sure effect. The deviation was the same at the two temperatures. 

 In spite of the high compressibility of strontium the deviation from 

 linearity was symmetrical about the mean pressure, so that it is pos- 

 sible to represent the changes of volume by a two constant formula, 

 which follows: 



AV 



At 30° — = - 10- 7 (81.87 - 72.5 X I0~ 5 p) p 



r 

 AV 



At 75° — = - 10- 7 (82.68 - 71.7 X I0~ 5 p) p. 



V 



