138 BRIDGMAN. 



Cr 2%, made by the Driver Harris Co. for use in heating units. I was 

 interested in the pressure and temperature coefficients because I had 

 used it as the capillary for containing liquid lithium. The accuracy 

 required in the coefficients was not high, so that measurements of the 

 pressure coefficient at only one temperature and of the temperature 

 coefficient between only two temperatures were sufficient. 



The specimen was in the form of a capillary 0.045 inches outside 

 diameter, and 0.032 inches inside diameter, about 6 cm. long. The 

 resistance was too low to be measured by the Carey Foster method, 

 and accordingly the potentiometer was used, as with other metals of 

 low resistance. The temperature of the pressure readings was 94.2°. 

 At this temperature the resistance decreases mth increasing pressure, 

 the relation is linear within the limits of error, and the average coeffi- 

 cient between and 12000 kg. is — O.OalTQO. Except for a single bad 

 point, the maximum departure of any reading from the linear relation 

 was 0.7% of the total effect, and the arithmetic mean of all the depar- 

 tures was 0.25%. 



The average temperature coefficient of resistance at atmospheric 

 pressure between 0° and 94° was 0.000684. 



General Survey of Results. 



We have in the first place to inquire whether these new results for 

 elements somewhat unusual in their properties are the same in char- 

 acter as those pre\'iously obtained for the more common elements. 

 In discussing the new data it will be convenient to discuss separately 

 metals in the solid and liquid state, and also metals with positive or 

 negative pressure coefficients of resistance. The pre^-ious results were 

 almost entirely for solid metals; measurements for only one liquid 

 metal, mercury, had been made at that time. Furthermore, the 

 pressure coefficient of all solids, except bismuth and antimony, was 

 negative. In the following a solid or liquid is called normal if its 

 pressure coefficient of resistance is negative. The alloys VAill require 

 separate discussion. 



Normal Solids. The normal solids embraced in the present series 

 of measurements are Xa, K, Mg, Hg, Ga, Ti, Zr, As, W, La, Xd, Si, 

 and black phosphorus. The special interest of these measurements 

 attaches to those substances with large coefficients. Many of the 

 above list do not belong in this category, and ma}' be dismissed with a 

 few words. 



