PIERCE. — CRYSTAL RECTIFIERS FOR ELECTRIC CURRENTS. 339 



Thermoelectromotive Force. — 

 Five specimens were mounted for 

 the study of the thermoelectromo- 

 tive force of molybdenite against 

 copper. These specimens are re- 

 ferred to as "A," "B," "C," "D," 

 and "E." The method of mounting 

 the specimen E is shown in Fig- 

 ure 8. A thin sheet of molybdenite 

 .1 or .2 mm. thick, 2 cm. wide, and 

 8 cm. long, was cemented between 

 two glass microscope slides G with 

 a cement made of water-glass and 

 calcium carbonate. 14 The molyb- 



Figure 8. Apparatus for determin- 



TEMPERATURE 

 60 80 100 120 



140 160 180 



denite was then copper-plated over ing thermoelectric force of molybdenite 



a small area at each of the exposed against copper. 



ends MM, and to these copper-plated areas were soldered copper wires 



.2 mm. in diameter, so as to form thermal junctions with the molybden- 

 ite. The thermal junctions and 

 the ends of the glass mounting 

 were inserted into two brass ves- 

 sels for containing the tempera- 

 ture baths of oil. The joints 

 between the brass vessel and the 

 glass mounting were made tight 

 with the cement of water-glass 

 and calcium carbonate. The oil 

 baths were provided with stirrers 

 driven by a motor. One of the 

 baths was kept at 0° C, and the 

 other bath was given various tem- 

 peratures between and 200° C 

 The resulting thermoelectromo- 

 tive force was measured by means 

 of a potentiometer to which the 

 copper wires LL led. The results 

 are recorded in Table VIII and 

 plotted in the curve of Figure 9. 



Figure 9. Thermoelectromotive force 

 of copper-molybdenite couple "E," for 

 various temperatures of hot junction. 

 Cold junction at 0° C. 



14 Otto Keichenheim suggests the 

 use of such a cement in Inaugural 

 Dissertation, Freiburg t 1906. 



