COMPRESSIBILITY OF METALS. 197 



Lead. This material was a melting point sample from the Bureau 

 of Standards. The analysis of this specimen had not been completed. 

 A presumably similar piece of purity 99.9948 is reported in detail in a 

 previous paper. 12 Two samples were prepared in two different 

 ways. The first was cast in a graphite mold, and chilled by lowering 

 the mold slowly into water while the upper part of the casting was kept 

 hot, in this way ensuring solidification from the bottom up without 

 the formation of flaws. This was seasoned by heating in oil to 200° 

 after easting. Its density at 20° was 11.347. It was machined to 

 0.75 cm. diameter and 16 cm. long, and was mounted in the apparatus 

 for direct measurement without multiplication. The second piece 

 was cast like the first, then extruded cold from a diameter of 1.5 to 

 0.75 cm., annealed at 230°, and measured in the same apparatus as the 

 first piece. Its density at 20° was 11.337. Neither specimen showed 

 any perceptible permanent set even after the first application of pres- 

 sure. 



Regular runs were made on each sample at 30° and 75°. The cast 

 sample gave points whose arithmetical departure from a smooth curve 

 (no discards) was 0.14%, and the maximum departure from linearity 

 averaged 3.1%. The average arithmetical departure from a smooth 

 curve of the points for the extruded sample (no discards) was 0.22%, 

 and the maximum deviation from linearity was 2.2%. It is remark- 

 able that both samples agreed in showing a departure from linearity 

 nearly 50% greater at the lower temperature, but this seemed to me 

 so unlikely, that I have preferred to regard it as due to a chance accu- 

 mulation of error, and have used the mean of the deviations at the two 

 temperatures in computing the final formulas, which are: 



AV 

 Casting, At 30° — = - 10~ 7 (23.73 - 17.25 X I0~ 5 p) p 



I 



o 



AV 

 At 75° — = - 10- 7 (24.33 - 17.7 X lO" 5 ?) p 



I 



o 



AV 

 Extruded casting At 30° — = - 10~ 7 (23.05 - 12.3 X 10- 5 p) p 



I 



a 



AV 



At 75° — = - 10- 7 (23.63 - 12.3 X lO^p) p. 



I 



o 



It is to be noticed that these two samples differ chiefly in their 

 pressure coefficient of compressibility; the average compressibility to 

 12000 kg. of the two samples is practically the same. 



