COMPRESSIBILITY OF METALS. 193 



of the difference of compressibility between uranium and iron is not 

 high. The results are embodied in the formulas: 



AT' 

 At 30° — = - 10- 7 (9.66 - 2.5 X 10" 5 p) p 



W 







AV 



At 75° 77- = - 10- 7 (9.55 - 2.2 X 10- 5 p) p . 



V 



It is to be noticed that the temperature coefficient of compressibility 

 seems to be negative. This is unusual, and perhaps is not genuine, 

 but I give the results as they were found because the magnitude of 

 this temperature effect is greater than the probable error. 



The compressibility of uranium seems not to have been previously 

 measured. The value found is not inconsistent with that which might 

 be expected from its position in the periodic table, but this is always 

 a rather inaccurate way of getting compressibility, and in the case of 

 uranium, because of its position at the end of the list of the elements, 

 it is a particularly poor way of guessing the compressibility. 



Silver. This I owe to the courtesy of Baker and Co. I have no 

 analysis, but it was said to be of the highest possible purity. It was 

 provided in the form of drawn rod 0.6 cm. in diameter and 12 cm. long. 

 It was annealed at a red heat before the measurements, and mounted 

 as a compression specimen in the lever apparatus for long specimens. 

 The density at 20° was 10.486. I also made measurements on another 

 similar piece of material in the lever apparatus for short specimens. 

 This was done before the final improvements had been made in the 

 apparatus, and the results were rather irregular, but agree with those 

 found for the other specimen within the limits of error. 



The regular two runs at 30° and 75° were made. The average 

 arithmetical departure from a smooth curve of the 28 readings (no 

 discards) was 0.4S% of the maximum pressure effect. The maximum 

 departure from linearity, which was sensibly the same at the two 

 temperatures, was 2.05%. The final results are given by the formulas ; 



AV 



At 30° — = - 10- 7 (9.87 - 4.4 X 10~ 5 p) p 



I 



o 



AT' 

 At 75° -=- = - 10- 7 (10.04 - 4.5 X 10- 5 p) p. 



J 







The initial compressibility found by Richards for silver of density 

 10.5 was 9.9 X 10 -7 . A. W. J. found no departure from linearity with 



