182 APPLIED SCIENCE 



temperature of the hot junction at the place where the 

 thermo-element is inserted. 



Inasmuch as the electric current produced in the thermo-ele- 

 ment through the heating of the hot junction depends on the 

 difference between the temperature at the two extremes of 

 the rods, it is, of course, essential that the outer ends of the 

 rods or the cold junction be kept cool. 



The insertion tubes are made in various lengths and fitted 

 with protection tubes and flanges (screwed couplings) to 

 adapt them exactly to the different processes or apparatus 

 for which they are required. The constituents of the thermo- 

 element vary according to the intensity of the heat for which 

 they are intended. For temperatures up to 1100 F. or 

 600 C., the element consists of nickel and a special metal 

 alloy; for temperatures up to 2300 F. or 1250 C., nickel 

 and a special carbon are used; while for temperatures up 

 to 2900 F. or 1600 C., platinum and platinum rhodium 

 give the best results. 



216. Galvanometers and the Measurement of Heat. 

 Galvanometers can also be used to measure temperature 

 because, as noted above, an electric current is formed when 

 metals are heated. The current thus produced is propor- 

 tional to the temperature to which the metal is heated. 

 Consequently, a galvanometer reading in current indirectly 

 measures the temperature. 



Galvanometers are used for the measurement of lower 

 temperatures up to 1100 F. They are hung vertically, 

 and the scale and finger are made very bold, so as to enable 

 the operator or workman to recognize the temperature at a 

 glance, without having to go close to the instrument. 



When used for scientific and other work requiring exact- 



