429 



TABLE 448.— VALUES OF DIELECTRIC CONSTANT FOR SEVERAL ELECTRIC 

 INSULATING MATERIALS AT RADIO FREQUENCIES 



Frequency Dielectric 



Material kc constant 



Glass 30 5.1-7.9 



cobalt 500 7.3 



crown 230 6.3 



800 6.2 



flint 500 7.0 



890 7.0 



photographic . . 100 7.5 



1700 7.4 



plate 500 6.8-7.6 



Pyrex 30 4.8 



500 4.9-5.8 



Marble 44 8.4 



80-650 9.2-11.7* 



1400 7.3 



Mica 100-1000 5.8-8.7 



Range of 10 samples of various kinds of marble. t After drying sample for 48 hours at 80°C. 



TABLE 449.— COMPARISON OF ELECTRICAL PROPERTIES OF INSULATING 

 MATERIALS AT ROOM TEMPERATURE** 



Intrinsic dielectric strength 



, — ; A v Volume 



Thickness Dielectric resistivity 



Material (mm) (Kv/cm) constant (ohm-cm) 



Cellulose acetate 025-.12 2300t 5.5 10 18 



Glass : 



borosilicate No. 7740 (Pyrex) .10 4800* 4.8 10 18 



soda lead 10 3100* 8.2 10" 



soda lime 10 4500* 7.0 10" 



Mica, muscovite clear ruby 020-.10 3000-8200t 7.3 10" 



Phenolic resin 012-.04 2600-3300t 7.5 10 u 



Porcelain, electrical — 380t 4.4-6.8 10 u 



Porcelain, steatite— low loss .. — 500t 6.0-6.5 10" 



Silica, fused — 5000* 3.5 10 18 



Rubber, hard 10-.30 2150t 2.8 lO 18 



** Table from Corning Glass Works publication on Properties of Selected Commercial Glasses (B-83). 

 * Values of P. H. Moon and A. S. Norcross, Trans. Amer. Inst. Electr. Engr., vol. 49, p. 775 (1930). 

 t Values of S. Whitehead. World Power, p. 72, September 1936. 



Intrinsic dielectric strength can be realized only under test conditions and is very much 

 higher than the working dielectric strength attainable in ordinary service. These data are 

 listed for purposes of comparison. 



SMITHSONIAN PHYSICAL TABLES 



