78 



GEOLOGICAL SURVEY OF ALABAMA 



terminals at 60 cycles, alternating current, the voltage 

 being applied gradually until the breakdown occurred. 



Average Voltage 



Per Mill. Thickness 



of Sample. 



1530 



4600 



4200 



Thickness of 

 Sample. No. Sample in Inches. 



1 0135 



2 0025 



3 00325 



The results of the test on samples Nos. 2 and 3 indi- 

 cate a high dielectric strength. 



The comparative low voltage per mill of sample No. 1, 

 was due to the condition of the sample, in that cracks 

 were present. 



CHAS. A. NASH, 

 Consulting and Testing Engineer, 



3300 Federal Street, Chicago, 111. 

 August 12, 1920. 



Report on electrostatic test of 12 samples of mica, sub- 

 mitted by the Consolidated Mica Company, from their 

 mines at Micaville, Alabama. 



PUNCTURE TEST ON MICA SAMPLES. 



Surface 

 Leakage 



3"_13440 

 2 y 2 " 14640 

 2 y 2 " 12480 

 2 y 2 "12240 

 2 y 2 "12000 



2%"' v 10500 



Samples with the exception of "D" were split because 

 of small size. 



Bottom electrode flat and 1" in diameter. 

 Top electrode %" sphere. 



INDIANA AND MICHIGAN ELECTRIC COMPANY, 



South Bend, Indiana. 

 August 19, 1920. 



