1891.] Heat produced by compressing Liquids and Solids. 185 



graduation or to allow the substance to be changed. The wires were 

 insulated by drawing them through tine india-rubber tubing of the 

 kind known as vein tubing. This arrangement proved very objection- 

 able in practice, as the oil and grease off the inside of the gun attacked 

 the rubber and ultimately perforated it, permitting contact with the 

 metal sides of the gun. 



Naturally, after this occurred, the results became perfectly irregular 

 and worthless, and the whole apparatus had to be taken to pieces in 

 order to renew the insulation. This was done by stripping off the 

 bad pieces of india-rubber and then covering the whole length of each 

 wire with a double thickness of narrow silk ribbon wound on and 

 whipped over with thread. After the renewal of the insulation there 

 was not a single defective result, and the readings vary within re- 

 markably narrow limits, as. will be seen by reference to the tables. 

 The outer or cold junction of the thermo-electric apparatus was im- 

 mersed in a large wooden tub of cold water, the temperature of which 

 changed but little from day to day, and might be regarded as perfectly 

 uniform during the performance of any experiments. 



The apparatus for containing the liquids which were subjected to 

 compression is represented in fig, 3. The wires of the junction are 



FIG. 3. Section of Tube. 



fixed into a hollow glass stopper, B, which was ground to fit the tube 

 C. This tube carried a slight flange at D, to which a disc of soft 

 black rubber could be tightly wired. This rubber disc served to close 

 the end of the tube and at the same time allowed perfectly free com- 

 munication of pressure from the outside to the inside of the apparatus. 

 A loop of thick copper wire was twisted round the neck of the tube 

 to furnish a handle by which it could be drawn out of the gun. In 



