PIERCE. — CRYSTAL RECTIFIERS FOR ELECTRIC CURRENTS. 323 



Figure 3. Mounting of molybdenite. 



periments on sound, 9 or it was mounted in a manner to permit of ready 

 adjustment, as is shown in Figure 3. The clamp K containing the mo- 

 lybdenite is metallically connected with the binding post H (Figure 3). 

 Another binding post is 

 attached to the metallic 

 block A, on top of which 

 is supported a stout 

 spring B. Through a 

 hole in B provided with 

 a set screw, the rod P 

 is allowed to drop down 

 into contact with K. 

 The set screw is then 

 tightened against P, and 

 the final adjustment is 

 made by the slow mo- 

 tion screw S. The apparatus is connected in circuit by means of the 

 binding posts, so that the current of the circuit is made to enter the 

 molybdenite through the contact area between P and the molybdenite 

 and leave by way of the contact between the molybdenite and the cap C, 

 or the reverse. It is found that a larger current flows in one direction 

 than in the reverse direction for a given applied electromotive force. 



Current- Voltage Characteristic of the Molybdenite Rectifier. — A large 

 number of current- voltage curves of the molybdenite rectifier with the 

 form of mounting shown in Figure 3 have been taken both with direct 

 and alternating applied voltages. Two sets of these curves, with the 

 corresponding tables, are here given. In taking the observations of 

 Figure 4, Table I, the rectifier was submerged in a constant tempera- 

 ture oil bath. The oil was rapidly stirred and had free access to the 

 surface of the molybdenite and to the point contact between the molyb- 

 denite and the copper rod. A steady voltage was applied to the termi- 

 nals of the rectifier, and the current through the crystal was measured. 

 The voltage was then reversed and the current again measured. The 

 process was repeated with various values of the voltage. These values 

 thus obtained in the oil bath were found to be the same as the corre- 

 sponding values when the rectifier was in air at the same temperature. 

 That is, the presence of the oil about the rectifying contact did not 

 materially affect the process. 



The values of Table I are plotted in the curves A and B of Figure 4. 

 A is the curve obtained when the current was sent from the copper to 



9 Loc. cit. 



