THE CALORIMETER SYSTEM AND MEASUREMENT OP HEAT. 113 

 THE THERMO-ELECTRIC ELEMENTS. 



Differences in the temperatures of the zinc and the copper walls are 

 indicated by a current of electricity generated by thermal junctions 1 of 

 iron and German-silver wire inserted between the metal walls and con- 

 nected with a reflecting galvanometer. There are in all 304 pairs of 

 such junctions distributed throughout the metal walls in groups, each 

 group containing four pairs of junctions and comprising what, for con- 

 venience, is termed an element. The thermo-electric element used in 

 this calorimeter is illustrated in figure 26. 



Construction of the element. Each element consists of four pairs of 

 j unctions of iron and German-silver wires, inserted in grooves in a wooden 

 cylinder. The iron wire consists of " soft, bright Bessemer steel wire, 

 Washburn & Moen gage No. 19." The other is so-called nickel 

 German-silver wire, 18 per cent, Brown & Sharpe gage No. 18. 

 Four short pieces of the iron wire were joined with silver solder, by 

 means of a blow-pipe, to three pieces of German-silver wire of the 

 same length and two pieces somewhat longer, and then bent in the 

 manner shown in figure 26, in which the iron wire is represented by 

 the solid black line. They were then crowded into slots in a short 

 wooden rod made of thoroughly seasoned, straight-grained, hard maple. 

 As is seen in figure 27, one of the long German-silver wires is doubled 

 on itself and brought out parallel to the other. By this arrangement 

 there are four soldered unions of iron and German- silver at each end 

 of the wooden rod. The ends of the German-silver wire are fastened 

 to copper wires leading to the galvanometer. The completed element, 

 as above described, is finally boiled for some time in paraffin to expel 

 moisture and insure perfect electrical insulation. 



Method of installing elements. The method of installing the elements 

 in the metal walls is illustrated in figure 28. 



The base of a copper thimble, 15 mm. in diameter and 16 mm. deep, 

 having straight sides, is soldered to the outer surface of the copper 

 calorimeter shell, i. e. , in the space between the zinc and the copper. 

 Directly opposite this thimble in the zinc wall, a copper ring, 15 mm. 

 internal diameter and 26 mm. long, is soldered in such a position that 

 it extends 13 mm. outside of the zinc wall. The thermo-electric ele- 

 ment is then slipped through the ring soldered in the zinc wall, and 

 the inner end of the element inserted into the thimble soldered to the 



1 The use of thermal junctions for this purpose was originally suggested by Dr. 

 R. B. Rosa. The use of this principle in cp.lorimetric work has been attended with 

 such excellent success that it is retained here, although the form of element has 

 been modified. The present form was devised by Mr. O. S. Blakeslee, formerly 

 mechanician of Wesleyan University. 



SB 



