395 



TABLE 401.— VOLUME AND SURFACE RESISTANCE OF SOLID DIELECTRICS 



The resistance between two conductors insulated by a solid dielectric depends both upon 

 the surface resistance and the volume resistance of the insulator. The volume resistivity, p, 

 is the resistance between two opposite faces of a centimeter cube. The surface resistivity, 

 <r, is the resistance between two opposite edges of a centimeter square of the surface. The 

 surface resistivity usually varies through a wide range with the humidity. 



a; megohms <x; megohms a; megohms p 



Material 509c humidity 70% humidity 90 r f humidity Megohm-cm 



Amber 6X10 8 2x10 s lXlO 5 5xl0 10 



Beeswax, yellow 6x10* 6X10 8 5X10' 2X10" 



Celluloid 5X10 4 2x10* 2X10 3 2X10 4 



Fiber, red 2X10* 3X10 3 2X10 2 5X10 3 



Glass, plate 5X10' 6X10 2x10 2X10 7 



" Kavalier 4X10° 4xl0 3 1X10 3 8X10° 



Hard rubber, new 3Xl0 9 1X10 8 2X10 3 1X10 12 



Ivory 5X10 3 1X10 3 3x10 2X10 2 



Khotinsky cement 7X10" 3X10 8 5x10 s 2X10° 



Marble, Italian 3X10 3 2X10 2 2X10 1x10 s 



Mica, colorless 2X10 7 4x10* 8X10 3 2X10 11 



Paraffin (parowax) 9XlO n 7X10° 6X10" 1X10 10 



Porcelain, unglazed 6X10 5 7X10 3 5x10 3X10 8 



Quartz, fused 3X10° 2X10 3 2X10 2 5X10 12 



Rosin 6X10 8 3X10 8 2X10 8 5X10 10 



Sealing wax 2X10 9 6X10 8 9X10 7 8X10° 



Shellac 6X10 7 3X10° 7X10 3 1X10 10 



Slate 9X10 3X10 1X10 1X10 2 



Sulfur 7X10° 4X10 9 1X10 8 lXlO 11 



Wood, paraffined mahogany 4X10° 5X10 5 7X10 3 4X10 7 



TABLE 402.— ELECTRICAL RESISTIVITY OF SOME OXIDES AND 

 MISCELLANEOUS MINERALS* 



Resistivity 



Material ohm-cm 



Graphite, commercial 



electrodes (density = 1.5) .001-.0013 



Hematite, Fe 2 3 , mineral.. .35-7 



Iron, metallic, meteoric . . . 2.4-3.2X6" 6 



Rock salt, pure 10M0 7 



impure 10" 



Resistivity 

 Material ohm-cm 



Sulfur >10 u 



Pb0 2 , synthetic 000092 



Mn0 2 , synthetic 6 



W 2 5 00045 



WO, 2X10 5 



For reference, see footnote 45, p. 136. 



TABLE 403.— ELECTRICAL RESISTIVITY OF ROCKS AND SOILS* 



Resistivity 

 Igneous rocks ohm-cm 



Granite 10 7 -10 9 



Lava flow (basic) 10M0 7 



Lava, fresh _ 3X10 5 -10 8 



Quartz vein, massive >10° 



Resistivity 

 Metamorphic rocks ohm-cm 



Marble, white 10 10 



Marble 4X10 8 



Marble, yellow 10'° 



Schist, mica 10 7 



Shale, Nonesuch 10 4 



Shale, bed 10 s 



Resistivity 

 Sedimentary rocks ohm-cm 



Limestone 10 4 



Limestone, Cambrian 10M0 5 



Sandstone, eastern 3X10M0 4 



Sandstone 10 6 



Limestone 10 5 



Resistivity 

 Unconsolidated materials ohm-cm 



Clay, blue 2X10 4 



Clavey earth 10MX10 4 



Clav, fire 2X10 5 



Gravel 10 5 



Sand, dry 10M0 6 



Sand, moist 10 5 -10 a 



* For reference, see footnote 45, p. 136. 

 SMITHSONIAN PHYSICAL TABLES 



