134 



Prof. C. I. Burton and Mr. W. Marshall. [June 18, 



FIG. 2. Section of Gauge. 



them between two broad washers of thick soft leather, and screwing 

 these as tightly as possible between the flanges at the lower end of 

 the gun. The leathers were prepared by soaking in warm lard in 

 racwo, as recommended by Professor Andrews. The arrangement was 

 found to hold pressure extremely well, if the bolts were tightened tip 

 each day before beginning the experiments. As it was necessary that 

 many of the liquids used should be completely protected from water, 

 we were obliged to choose wires for the junction which could be sealed 

 through glass. After experiments with a large number of different 

 pairs of metals, beginning with pure platinum and going up to 33 per 

 cent, of iridium, specimens of commercial platinum and an alloy of 

 platinum with 10 per cent, of iridium were selected. Strange to say, 

 nearly the same current was obtained from a junction of two different 

 samples of 10 per cent, iridium. 



The platinum wire was of about No. 24 B.W.G., the alloy wire of 

 0" 029 diameter. The latter resembled steel in its properties, being- 

 very hard and elastic. Its thickness was a disadvantage, because it 

 increased the mass of the junction and caused a sensible time to elapse 

 before the wires attained the temperature of the liquid during the 

 experiments. The wires were welded to form the junction and 

 hammered thin and flat in order that the contact with the substance 

 under trial might be as perfect as possible. A length of about 3 feet 

 of the double wires was coiled into a spiral spring inside the gun, so 

 that the junction end could be drawn out at the top either for 



