THE EFFECT OF PRESSURE ON THE ELECTRICAL 



RESISTANCE OF COBALT, ALUMINUM, NICKEL, 



URANIUM, AND CAESIUM. 



By P. W. Bridgman . 



Presented October 11, 1922. Received October 18, 1922. 



Introduction. 



In former numbers of the Proceedings of the American Academy 1 

 I have given data for the effect of pressure on the resistance of 39 of 

 the elements. It is my intention to keep this work as up-to-date as 

 possible by the revision of the previous data or the inclusion of new 

 substances; this paper is in the nature of such a supplement to the 

 former work. The first three of the metals above have been previ- 

 ously investigated, but I have now been able to obtain them in a state 

 of considerably higher purity than formerly, so that a redetermination 

 of the pressure effect was worth while. The pressure coefficients now 

 found for these purer samples are of the order of 10% higher than the 

 previous values. Measurements on uranium have not been made 

 before; the specimen I had was presumably not of very great purity, 

 but since even the sign of the coefficient was not known, and since as a 

 general rule impurity does not greatly affect the pressure coefficient, 

 it was of interest to make and record the measurements. The work 

 on ceasium is not yet complete, but enough has been done to establish 

 the existence of surprising phenomena for this element, and since it 

 may be some time before I shall be able to complete the work, it 

 seemed that announcement of the chief fact should not be delayed. I 

 have found that caesium has a new polymorphic modification under 

 high pressure, of smaller volume than the ordinary modification, but 

 that the resistance of this new modification increases instead of de- 

 creases under pressure. Since caesium is the most compressible of the 

 metals, this result may be of significance in suggesting what may 

 happen to all metals at pressures sufficiently extreme. 



Detailed Data. 



Cobalt. The former sample of cobalt was obtained from Dr. 

 Herbert T. Kalmus who had prepared it in the course of an investiga- 

 tion of the properties of metallic cobalt for the Canadian Government. 

 This was one of the impurer of the samples which he prepared, but 



