CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL 

 LABORATORY, HARVARD UNIVERSITY. 



ON ELECTRICAL PROPERTIES OF CRYSTALS. 



I. STRATIFICATION AND CAPACITY OF CARBORUNDUM. 



By Geoege W. Pierce and Rhys D. Evans. 



Presented by G. W. Pierce, February 14, 1912. Received February 1, 1912. 



This work is a continuation of some investigations by one of us on 

 Crystal Rectifiers for Alternating Currents. * 



Capacity of Carborundum. — In the experiments that are described 

 in the present paper it has been found that a fragment of carborundum, 

 with certain attachments of the electrodes, shows a large electrostatic 

 capacity. Measurements are given of this capacity in two typical 

 cases. 



Character of the Phenomenon. — The discussion of the measurements 

 is followed by an account of a microscopic and electrical investigation 

 of the carborundum, which shows that the carborundum crystal is made 

 up of an insulating mass permeated by fine layers of conducting ma- 

 terial. These conducting layers are nearly parallel, and, separated as 

 they are in the crystal by non-conducting sheets, form a natural elec- 

 trical condenser, provided electrical contacts are made to two conduct- 

 ing layers or sets of layers that do not happen to short-circuit within 

 the crystal. 



Method of Measuring the Capacity of the Crystals. 



Method of Charge and Discharge. — The capacity of the carborundum 

 crystals was measured directly by a method of charge and discharge. 

 A simplified diagram of the circuits employed is shown in Figure 1. 

 By means of a motor-driven commutator C the crystal Cr was con- 



^ G. W. Pierce: "Crystal Rectifiers for Electric Currents," Part I, Physi- 

 cal Review, 25, pp. 31-60, 1907; Part II, ibid., 28, pp. 153-187, 1909, and 

 These Proceedings, 44, pp. 317-349, 1909; Part III, Physical Review, 29, pp. 

 478-484, 1909. See also " A Simple Method of Measuring the Intensity of 

 Sound," These Proceedings, 43, 1908, and " Principles of Wireless Telegraphy," 

 McGraw-Hill, New York, 1910. 



