44 BRIDGMAN. 



For the theoretical considerations suggested by these measurements 

 it is necessary to know the mechanical deformation produced by the 

 tension, that is, to know Young's modulus. I have determined this 

 for most of the metals. The metals were in most cases too soft to 

 allow a direct determination by hanging a weight on the wire and 

 observing the change of length, so that an indirect method was neces- 

 sary. The method I used was that of flexure. A horizontal wire of 

 known length and section was bent by a weight hung on the free end, 

 and the amount of the flexure of the free end determined. From this 

 Young's modulus can be calculated. The calculation assumes the 

 perfect isotropy of the wire. It is probable that this condition is not 

 always satisfied to as high a degree of approximation as would be 

 desirable, but under the conditions it seemed the best that I could do. 

 The modulus for manganin and therlo was determined directly. 



The difficulties of the resistance measurements vary greatly for the 

 different metals. The effect is in any event small, and for those 

 metals which are soft and have a low elastic limit, the magnitude of 

 the maximum effect is sometimes not greatly in excess of the order of 

 magnitude of the accidental errors. An additional difficulty for the 

 metals Li, Sr, and Ca is that of making electrical connections. These 

 metals cannot be soldered, and mechanical spring clamps had to be 

 used. The resistance at the contact would sometimes vary sufficiently 

 to produce perceptible fluctuations in the main current, and also the 

 potential terminals were sometimes subject to slight displacements 

 under the stirring by the oil. The details of these difficulties will be 

 described under the metals separately. 



I am indebted to the skill of my assistant, Mr. J. C. Slater, for 

 practically all the actual readings. 



Here follows a description of the details for each metal. 



Detailed Data for Individual Metals. 



Lithium. The material was from Merck, for which I have no 

 analysis. It was apparently entirely free from inclusions of slag, and 

 mechanically homogeneous. Metal from the same lot was used in 

 previous determinations of the pressure coefficient of resistance.^ It 

 was formed into wire of about 0.032 inches diameter by cold extrusion, 

 in the usual way. The surface of the wire so formed is bright, and it 



5 P. W. Bridgman, Phys. Rev. 56, 59-154, 1921. 



