PRESSURE OX RESISTANCE OF METALS. 



587 



ordinates of the several curves is changed so as to make the resistance 

 at kg. independent of the temperature, the curves corresponding to 

 the higher temperatures M'ill drop off more sharplj', and will also have 

 greater curvature. This is entirely as one would expect, particularly 

 if the curves are asvTnptotic to zero resistance at infinite pressure. 



Tin. This was Kahlbaum's best, grade "K." It was extruded to 

 O.OOS inch diameter and wound bare on a bone core. Its resistance 

 at 0° and 1 kg. was 12.3 ohms. Connections were made by soldering 

 with a fusible alloy of tin and lead of melting point about 180°. It was 

 seasoned by heating to 120°, and by a preliminary^ application of 12000 

 kg. at 25°. Extrusion instead of drawing proved necessary. It was 

 possible to draw the wire down to 0.01 inch, but there were many 

 irregularities and it was not possible to wind it with silk insulation. 

 Several unsuccessful preliminary attempts were made with the bare 

 extruded wire on a hard rubber core. There were large initial irregu- 

 larities due to the large thermal expansion of the hard rubber which 

 entirely disappeared on using bone. With the final set-up the perma- 

 nent change of zero after a run to 12000 was never more than 0.1% 

 of the pressure effect, except at 0°, where the change jumped to 1%, 

 probably because of viscosity of the transmitting medium. 



Runs successful in every way were made at all five temperatures. 

 The smoothed results are collected in Table II, and the experimental 

 points are shown in Figure 4. Except for a single discordant point, 



TABLE II. 

 Tin. 



