594 



BRIDGMAN. 



run was made on this specimen at 100° before the cylinder broke; the 

 average coefficient of this specimen at 100° was 0.5% lower than that 

 of the pure specimen. tfiitiM 



The smoothed results are collected in Table V and the experimental 

 points are shown in Figure 7. The maximum departure of any single 

 point from the smooth curve was 0.2% of the total pressure effect, 

 and the average numerical departure was 0.026%. The deviation 



.U4I /U^o Tni 



40° 60° 80° 100° 

 Temperature 



Lead 



Pressure, Kg./Cm.'X 10' 



Figure 7. Lead, results for the measured resistance. The deviations 

 from linearity are given as fractions of the resistance at kg. and 0°C. The 

 pressure coefficient is the average coefficient between and 12000 kg. 



from linearity is very nearly symmetrical and parabolic, but there are 

 distinct failures of symmetry in the usual direction. It is very notice- 

 able at the higher temperatures that the curvature of the deviation 

 curves is greatest near the maximum. This is vmmistakably indicated 

 by the data. The deviation curves are also given in Figure 7. 



The temperature coefficient of the lead given in the table is 0.004207. 

 The coefficient of a piece of the same lead, which had never been 

 subjected to pressure, was found to be 0.00441. This value was 

 found by extrapolation of the readings between 25° and 96°. It is 

 this which is strictly comparable with the value 0.00428 of Jaeger 

 and Diesselhorst ^ for Kahlbaum's "K" lead. 



The initial pressure coefficient at 0° is given by Lisell ^ as — O.O4I4O. 

 Williams ^^ found the relation between resistance and pressure to be 

 linear over a range of 700 kg. and the value of the coefficient to be 

 — O.O4I38. The value found above by graphical extrapolation from 



13 W. E. Wilhams, Phil. Mag. 13, 635-643 (1907). 



