COMPRESSIBILITY OF METALS. 191 



both when one considers the mechanical softness of the metal, and 

 also that its position in the periodic table below copper and silver 

 suggests a compressibility following the succession of values of these 

 two other metals, which would lead to a figure more than twice as high 

 as the actual one. 



Copper. Copper from two sources was used. One was commercial 

 drawn rod 0.6 cm. in diameter. Two sets of runs were made with 

 this, the first with the rod in the commercial drawn condition, and the 

 second after annealing. The second grade of material was pure copper 

 from the Bureau of Standards, cut from one of their melting point 

 samples, and had the following analysis: Sb 0.004, As 0.0020, S 0.0026, 

 Cu 99.987. This second sample was measured only in the annealed 

 condition. Both samples were mounted as compression specimens in 

 the lever apparatus for long specimens ; it was necessary to dowel to- 

 gether two pieces of the pure copper in order to get the requisite length, 

 which was 12 cm. In addition to the runs on these long samples, at 

 least four runs were made with preliminary forms of apparatus on 

 shorter samples of the pure copper. The accuracy was not as high as 

 in the final runs, and it is not necessary to describe the details, but 

 within the somewhat wider limits of error, the results of these prelimi- 

 nary measurements agreed with the final results. It was during the 

 preliminary measurements that an attempt was made to find a differ- 

 ence of compressibility of copper in different directions, with negative 

 results. 



The commercial copper was quite unusual in that it showed evidence 

 of internal strains. The readings both before and after the annealing 

 were affected by considerable hysteresis, and after the annealing the 

 first application of pressure produced a rather large permanent dis- 

 tortion. The average arithmetical deviation from a smooth curve 

 of the results for the unannealed copper (two discards) was 2.6 % of 

 the maximum pressure effect. Almost the entire amount of this 

 deviation is due, not to irregularity of the individual points, but to 

 hysteresis, which at the maximum was 5.5% of the maximum pressure 

 effect. For the commercial annealed copper the average arithmetical 

 deviation from smoothness was 1.6% of the maximum effect, and the 

 greatest width of the hysteresis loop was 5.5%. The loop was of a 

 different shape from that of the unannealed copper. The pure copper 

 from the Bureau of Standards showed no hysteresis; the average 

 arithmetical departure (no discards) from a smooth curve was 0.47%, 

 and the maximum departure from linearity was 1.44%. The results 

 are contained in the following formulas: 



