PRESSURE ON RESISTANCE OF METALS. 



593 



are scaled to the same initial resistance, the curves for the higher 

 temperatures are steeper, but are less curved. 



Lead. I owe this material to the kindness of Mr. C. Wadsworth, 

 who prepared it under the direction of Professor T. W. Richards 

 in connection with determinations of the atomic weight of lead of 

 ordinary and radio-active origin. It showed by spectroscopic analysis 

 not more than 1 part in 300,000 of Ag and Cu, and no trace of any 

 other metal. It was made into wire 0.013 inch diameter by cold 

 extrusion, wound loosely on a bone core as usual, and connected to the 

 leads with "fine" soft solder. Its initial resistance at 0° was 11.0 

 ohms. It was seasoned by preliminary applications of 12000 kg. at 

 50° and 100°. 



TABLE V. 

 Lead. 



The temperature coefficient of this excessively pure lead was com- 

 pared with that of Kahlbaum's "K" lead, formed into w^ire of the 

 same dimensions by extrusion in the same way. The coefficient of 

 Kahlbaum's lead was 0.2% lower than this, thus again confirming 

 this test of purity. 



An unsuccessful attempt, terminated by a flaw in the cylinder, 

 was made about two months before the successful runs. This first 

 run was on Kahlbaum's "K" lead, drawn from 0.06 to 0.01 inch and 

 silk insulated by the New England Electrical Works. It was very 

 fragile, with many places of incipient break. One break was made in 

 winding, and it had to be soft soldered in the center. A successful 



