COMPRESSIBILITY OF METALS. 195 



The final results are given by the formulas : 



AV 

 Drawn rod, Hard, At 30° — = - KH (13.40 - 3.5 X 1Q- 5 p) p 



I 



o 



AV 

 Drawn rod, annealed, At 30° — = - 10- 7 (13.34 - 3.5 X 10- 5 p) p 



V 



AV 



At 75° 77- = - 10- 7 (13.91 - 3.5 X 1CH p) p 



1 



o 



AV 

 Casting At 30° — = - 10~ 7 (13.43 - 5.0 X 10~ 5 p) p 



I 



' o 



AV 

 At 75° — = - 10- 7 (13.76 - 5.1 X 10- 5 p)p. 



I 







Some time ago I found the average compressibility to 6000 kg. of a 

 piece of commercial aluminum rod to be 11.7 X 10 -7 , distinctly lower 

 than the values found above. These early readings were not accurate 

 enough to show a departure from linearity. The specimen showed set 

 on the initial application of pressure, but otherwise there was no evi- 

 dence, such as hysteresis, of internal strain. Richards has found the 

 compressibility of aluminum of unstated analysis of density 2.60 

 to be 14.1 X 10~ 7 , somewhat higher than the above. A. W. J. for 

 aluminum containing 0.235% Si and 0.016% Fe were not able to detect 

 any departure from linearity over the range of 12000 kg., and give for 

 the average compressibility (corrected by my new value for iron) 

 12.7 X 10 -7 , which agrees to the third figure with the value given by 

 the above formula for cast aluminum. 



Germanium. The crystal structure of this substance has not yet 

 been published; I owe to the kindness of Dr. A. W. Hull of the General 

 Electric Company the information given in personal correspondence 

 that X-ray analysis shows it to be cubic, of the same type of lattice 

 as diamond and silicon. 



For the sample of germanium I am indebted to the kindness of 

 Professor C. C. Bidwell of Cornell University, who in turn obtained it 

 from Professor L. M. Dennis of the Cornell Chemistry Department. 

 It is the same specimen as that whose electrical properties he has 

 reported in the Physical Review. 11 The material is evidently ab- 

 normal in some way, because the electrical resistance behaves normally 

 below 100°, but above 100° decreases instead of increasing with rising 

 temperature. The specimen was in the form of a casting about 2.5 



