ELECTRICAL RESISTANCE UNDER PRESSURE. 139 



Mg and W were measured in the pre\dous paper. Except for the 

 improvement in the numerical values afforded by the new measure- 

 ments, these substances require no further discussion. It is to be 

 noticed that the revised values of the pressure coefficient are in such 

 a direction as to make the pressure coefficients of atomic amplitude 

 and resistance even more divergent than was found previously.^ 



La and Nd are the first metals of the rare earth group whose pres- 

 sure coefficients of resistance have been measured. The coefficients 

 of both these substances are not distinguished in any particular way 

 over those of the elements of the previous paper, and do not require 

 further discussion. 



Ti and Zr also belong to a class of elements not previously measured. 

 There was considerable impurity in these materials, and the results 

 have no considerable accuracy. The results are chiefly remarkable 

 for the smallness of the coefficients, which are smaller than for any 

 other pure substances measured. It is even possible that Ti belongs 

 to the abnormal metals, and that its resistance increases with increas- 

 ing pressure, but the experimental accuracy was not high enough to 

 allow this to be stated with certainty. 



Arsenic is a substance wliich might be expected to show abnormal 

 results because of its position in the periocHc table, but it is actually 

 found to be quite normal both in regard to the sign of the coefficient 

 and its magnitude. 



Gallium is another substance for which abnormal results were 

 expected because of its anomalous property of expanding on freezing. 

 The coefficient is however, normal in sign and magnitude. The accu- 

 racy of the measurements was not great enough to gi^'e the variation 

 of the pressure or temperature coefficients over the range open to 

 measurement. 



Solid mercury has been here measured for the first time over a 

 restricted range. It is quite normal with regard to sign and size of 

 the coefficient. 



Silicon and phosphorus are non-metallic in character, and wall be 

 discussed later. This leaves of the above list of normal metals only 

 the alkali metals sodium and potassium as needing special comment 

 because of the magnitude of their coefficients. Of the metals previ- 

 ously studied lead was found to have the greatest coefficient, the resist- 

 ance under 12000 kg. being 14% less than under atmospheric pressure. 

 Contrasted with this is a decrease of over 40% in the resistance of 

 sodium and over 70% in that of potassium under a pressure of 12000 

 kg. The question is whether substances with such high coefficients 



