The Electrical Conductivity of Calcite. — By W. J. Jack- 

 son, M.A,, McGregor Fellow in Physics, Dalhousie Uni- 

 versity, Halifax, N. S. 



(Read May 21, 1923) 

 It has been found that in crystals of calcite there is a polarisation effect 

 due possibly to a space charge near the electrodes or throughout the crystal; 

 the amount varying with different crystals. There is a displacement current 

 as well as a conduction current. The relation between the current and the 

 temperature is approximately exponential. The conductivity is directional. 

 When the crystals are exposed to X-Rays the change in conductivity does 

 not last for more than one or two hours. 



Introduction 

 Experimental work on the thermo-luminescent properties 

 of calcite and similar crystals has been carried out by Mackay* 

 in which he found that when the crystals became luminescent 

 the electrical conducitvity increased. The photo-electric con- 

 ductivity of diamond crystals has been recently investigated 

 by Miss Levi,t who found that the electrical resistance of dia- 

 mond crystals varied with the wave-length of the exciting light. 

 In a paper on the change in the electrical resistance which 

 certain crystals undergo on exposure to radiation, Gudden and 

 Pohl| offer an hypothesis that conduction takes place by means 

 of negative carriers, which on becoming separated from neutral 

 atoms leave them positively charged; the positive ions then 

 create a space charge within the crystal. 



Apparatus and Method of Measurement 

 Crystals of calcite were selected from a larger block of 

 calcite which was thermo-luminescent. 



Electrodes were fastened to the parallel faces by drilling 

 the calcite and fastening in copper wires with an amalgam 

 cement (dental). The approximate size of No. 1 crystal was 

 (2 cm. X 5 cm. X .75 cm.) and No. 2 (2.5 cm. X 2.5 cm. X 

 1 cm.) 



After the crystals had been carefully cleaned with alcohol 

 and dried they were mounted as shown in the diagram. 



* Proc. Roy. Soc. Canada. Vol. XV. Page No. 241; 1921. 

 t Proc. Roy. Soc. Canada. Vol. XVI., Page No. 95; 1922. 

 X Zeitschr. Fur Physik No. 6. Page 249. No. 7. Page 65; 1921. 



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