EFFECT OF PRESSURE ON CONDUCTIVITY OF METALS. 



91 



A scale drawing of the longitudinal specimen mounted in the 

 massive copper block ready for assembly in the pressure cylinder is 

 shown in Figure 3. 



The sink at one end of the specimen was formed by soldering it into 

 a massive copper block of a diameter nearly the same as the interior 

 of the pressure cylinder. Good thermal contact between the copper 

 block and the cylinder was ensured by a centering arrangement of 

 springs of strip metal, exactly as in the case of the cylindrical speci- 

 mens, except that now the strips were made of heavy copper instead 

 of thin german silver. In order to reduce mechanical distortion due 

 to unequal compression of the specimen and the copper of the block, 

 the bottom of the hole in the block into which the specimen was 



Figure 3. Longitudinal section of the pressure cylinder with the longi- 

 tudinal flow specimen attached to the three terminal plug and in place. 



soldered was brought into connection with the pressure transmitting 

 medium by a small drilled hole. 



The source of heat at the other end of the specimen was provided 

 by a small coil of nichrome wire 0.005 inch diameter and exactly 1 

 inch long, silver soldered to copper leads of the same diameter. The 

 resistance was of the order of two ohms. This wire was wound into a 

 coil of small dimensions on a core of a fine piece of glass tubing, and 

 was placed in a small copper capsule in the form of a square bottomed 

 cup about 2.5 mm. deep. One end of the heating coil was grounded 

 to the cup with solder, and the other end was connected to a lead 

 from the three terminal plug. The copper capsule was let into a hole 

 of the proper dimensions drilled in the end of the specimen. By the 

 use of the capsule I hoped to more nearly realize a uniform heat input 

 over the entire cross section of the specimen. To further realize these 



