ELECTRICAL RESISTANCE UNDER PRESSURE, 67 



and construction previously employed in measurements of resistance 

 or thermal e.m.f. under pressure were observed here also. 



The methods of computation were essentially the same as those 

 which ha\'e been described in great detail in the previous paper. Any 

 slight modifications were entirely obvious, and it is not necessary to 

 describe them further. 



A description in detail of the results obtained for the separate 

 substances now follows. 



Detailed Data for Individual Substances. 



Lithium. Two distinct series of measurements were made on this 

 substance, at two different times. The first series was on the pressure 

 coefficient of the solid, in the spring of 1919. It was found that the 

 pressure coefficient is positive, and large. This result was so sur- 

 prising in view of the high compressibility of the metal, and its close 

 relation to sodium and potassium, both of which have a very high 

 negative coefficient, that a correlation of this positive coefficient with 

 other properties of lithium was desirable. For instance, does lithium 

 expand in freezing, like bismuth, and if so, is this connected in any way 

 with the positive coefficient? But on looking up the data I could not 

 find that the melting data for lithium had ever been determined. It 

 was not even known whether lithium expands or contracts on melting. 

 The second series of measurements, in the winter of 1919-20, was 

 concerned with the effort to obtain some of the missing data. In 

 particular, it was desirable to find the volume relations on melting, 

 and to find whether the pressure coefficient of the liquid is positive as 

 well as that of the solid. I had already found that the positive coeffi- 

 cient of solid bismuth changes to negative on melting. 



The first series of measurements, on the resistance of the solid, was 

 made on lithium from Merck, prepared a number of years ago, but 

 kept under oil in sealed glass since then. A chemical analysis by 

 Mr. N. S. Drake showed 0.7% Al, and a trace of Fe. Sodium, if anj^, 

 could not be determined because only one gram of the lithium was 

 available for analysis. The method of preparation by electrolysis 

 should not allow much impurity of sodium if ordinary care is exercised. 



The lithium was extruded cold through a steel die into \\are 0.030 

 inches in diameter, and wound bare onto a bone core. Connections 

 were made at the ends with spring clips. So far as I am aware, no 

 previous measurements have been made on the properties of bare 



