COMPRESSIBILITY OF METALS. 187 



One was a piece of commercial nickel obtained from the International 

 Nickel Company in the form of a drawn bar 0.75 cm. in diameter and 

 16 cm. long. The purity was high commercial purity, a little better 

 than 99%. It was annealed by heating for several hours to a bright 

 red after its final machining, and was used as a compression specimen 

 in the lever apparatus for long specimens. The second sample piece 

 of nickel was obtained from the research laboratories of the Leeds 

 and Northrup Company, and was of very unusually high purity. It is 

 the same material as that for which I have already published data for 

 the effect of tension on resistance 9 and pressure on thermal conduc- 

 tivity. 10 I have no chemical analysis, but have determined the tem- 

 perature coefficient of resistance between 0° and 100° to have the 

 mean value 0.00634, which is very high. This material was provided 

 in the form of small cast ingots a couple of mm. thick and 5 or 6 cm. 

 long. There were flaws in these castings large enough to be visible 

 to the eye. I tried to get rid of these flaws by forging the castings to 

 considerably smaller dimensions. The forged castings were mounted 

 as compression specimens in the lever apparatus for long specimens, 

 and their compressibility measured, but there was a rather large 

 permanent set on the first application of pressure, and the relation 

 between pressure and deformation showed a rather large amount of 

 hysteresis. In order to get rid of the effect of the flaws, therefore, 

 this forged piece was drawn down to wire of 0.079 cm. diameter, 

 annealed at a bright red after the last drawing, and used as a tension 

 specimen in the lever apparatus for long specimens. 



The regular series of readings were made on each specimen, at 30° 

 and 75°. The average arithmetical deviation from a smooth curve of 

 the readings on the commercial rod (no discards) was 0.8% of the 

 maximum pressure effect. The corresponding average deviation 

 from a smooth curve of the readings on the wire, making three dis- 

 cards (it is usually true that the tension specimens do not give such 

 regular results as the compression specimens) was 1.1% of the maxi- 

 mum effect. Neither specimen showed any perceptible deviation from 

 linearity, which means of course that the variation of compressibility 

 with pressure is the same for nickel as for iron. 



The final results are as follows : 



AV 

 Commercial rod, At 30° 77- = - 10" 7 (5.25 - 2.1 X KHp) p 



I 



AV 

 At 75° — = - 10- 7 (5.28 - 2.1 X 10^p) p 



Vo 



