The diëlectric constant measurement of powdered regular crystalline solids

Abstract

In measuring t i e D.C. of a powder a grain-size effect must bz taken into account.For r,/fr ratio':; up to 3 special precautions will not he necessary. lor ratio's up to 6 the effect may be eliminated by using a large condenser (500 cm?) and a powder of fine grain-size (0.02 m m ) .Former measurements of several authors cannot be relied upon, thc grain-size effec': not having been taken into account. Measurements of the D.C. of NaCl and KCI powder at different fillingfractions under ideal conditions of powder-sizes and of NH,CI and KC1 floating in CCI,-C,,H, prove that the Biitfcher and Wiener-Bruggcrnan powder-formula'. give good results. In contrast with liquids the accurate D.C. measurements of solids meets with several difficulties. Each of the four methods, which may be used has certain disadvantages which makes the result of the measurement less accurate than would he desired: 1. Capxifly mcasurcnient of largc, flat-grohnd discs of crystal, ccpippcd with r?lcta/ elccfrodcs. From the dimensions of the crystal and the measured capacity the D.C. of the solid may be calculated directly with the aid of Kirchhofj's formula 1 ) c = capacity of a circu!ar condenser r = radius d = plate distance T h e disadvantages in this c x e m e : ( a ) Difficulties concerning the exact measurement of the physical dimensions of the crystal. ( b ) Uncertainty about the edge-correction terms in Kirchlioff's formula : I ) .