200 BRIDGMAN. 



of the density and thermal expansion. 13 This block was perfectly 

 free from any flaws on the exterior, but in cutting it in two preparatory 

 to getting out a smaller specimen, an inclusion of slag was found in the 

 very center. The previous measurement of density must therefore 

 have a small error, and the value for the expansion also an error, but 

 presumably not so large. On making a second cut no new inclusion 

 was found. A clean piece was got from the original cylinder approxi- 

 mately 1.3 cm. in diameter, and this was extruded at a temperature 

 of 450° to 0.6 cm. in diameter. A piece 10.5 cm. long was finally 

 obtained and mounted in the apparatus for direct measurement. Its 

 density at 20° was 1.555 against the previous value 1.556. 



The second piece I owe to the kindness of Professor C. C. Bidwell. 

 I do not know the origin, but it was stated to be of unusually high 

 purity. This was originally of roughly square section 1.6 cm. in 

 diameter. It was extruded in two steps at 450°, first to a round sec- 

 tion 1.3 cm. in diameter, and then to 0.6 cm. diameter. The final 

 length was the same as that of the other piece, and it was measured in 

 the same apparatus. Its density at 20° was 1.532. 



Professor F. A. Saunders was kind enough to make a spectroscopic 

 analysis of these two samples for me, with the following results: 



Calcium from General Electric Co.: Sr, considerable, perhaps 1 to 

 5% (2% would account for the difference of density), Cu trace, Mg 

 trace, Al trace, Si trace. 



Calcium from Professor Bidwell; remarkably pure, Mg trace, 

 Cu trace, nothing else. 



The regular runs at 30° and 75° were made on each specimen. 

 The average arithmetical departure from a smooth curve of the points 

 from the sample from the General Electric Co. (no discards) was 

 0.14%, and the maximum departure from linearity was 3.55% of the 

 maximum pressure effect. The corresponding values for the sample 

 of Professor Bidwell were (one discard) 0.11% and 3.7%. In spite of 

 the high compressibility of calcium, the departure from linearity was 

 symmetrical about the mean, so that it is possible to represent the 

 results by a two constant formula. The results follow: 



Calcium from General Electric Co., 



AV 

 At 30° -=r = - 10- 7 (59.46 - 48.8 X 10- 5 p) p 

 > o 



AV 



At 75° r- = - 10- 7 (59.67 - 48.8 X 10- 5 p) p. 



I 



