423 



TABLE 434.— DIELECTRIC STRENGTH OF MATERIALS 



Potential necessary for puncture expressed in kilovolts per centimeter thickness 



of the dielectric 



Kilovolts 

 Substance per cm 



Ebonite 300-1100 



Empire cloth .... 80-300 



" paper 450 



Fiber 20 



Fuller board 200-300 



Glass 300-1500 



Granite (fused) .. . 90 



Guttapercha 80-200 



Impregnated jute . 20 



Leatheroid 30-60 



Linen, varnished. . 100-200 



Liquid air 40-90 



Mica : Thickness 



Madras .1 mm 1600 



1.0 " 300 



Bengal .1 " 2200 



1.0 " 700 



Canada .1 " 1500 



1.0 " 500 



South America. 1500 



Micanite 400 



Substance 



Oils: 

 Castor 



Cottonseed 

 Lard 



Linseed, raw 



boiled 



Lubricating . . 

 Neatsfoot 



Olive 



Paraffin 



Sperm, mineral 



" natural 



Turpentine 



.2 

 1.0 



.2 

 1.0 



.2 

 1.0 



Kilovolts 

 per cm 

 Thickness 



.2 mm 190 

 1.0 " 130 



70 



140 



40 

 185 



90 

 190 



80 



50 

 200 



90 

 170 



75 

 215 

 160 

 180 



85 

 195 



90 

 160 

 110 



.2 

 1.0 



.2 

 1.0 



.2 

 1.0 



.2 

 1.0 



.2 

 1.0 



.2 

 1.0 



Kilovolts 



Substance per cm 



Papers : 



Beeswaxed . . 770 



Blotting 150 



Manilla 25 



Paraffined .. 500 



Varnished ... 100-250 



Paraffin : 



Melted 75 



Melt, point 



Solid 43° 350 



47° 400 



52° 230 



70° 450 



Presspaper 45-75 



Rubber 160-500 



Vaseline 90-130 



Thickness 



Xylene .2 mm 140 



1.0 " 80 



TABLE 435.— DIELECTRIC CONSTANT (SPECIFIC INDUCTIVE CAPACITY) 



OF GASES 



Atmospheric pressure 



Wavelengths of the measuring current greater than 10000 cm 



TABLE 436.— VARIATION OF THE DIELECTRIC CONSTANT WITH 

 THE TEMPERATURE 



If K = the dielectric constant at the temperature 0°C of the above table, K« at the tem- 

 perature t"C, and a and /3 are quantities in the following table, then K ( = K» — a (t — 0) 



+ P(t-ey. 



Ammonia o = 5.45 X 10" 5 ft = 2.59 X lO" 7 Range, 15-110°C 



Sulfur dioxide 6.19 X 10" 5 1.86 X 10' 7 0-110 



Water vapor 1.4 X 10"* .... 145 



The dielectric constant of air at 76 cmHg and varying temperature may be calculated 

 since K — 1 is approximately proportional to the density. See Table 437. 



SMITHSONIAN PHYSICAL TABLES 



