392 BELL SYSTEM TECH NIC A L JOURNA L 



electric constants of sodium chlorate (NaClOs) and sodium bromate 

 (NaBrOs) have been measured over a wide temperature range. The value 

 of the piezoelectric constant at room temperature is somewhat larger than 

 that found by Pockels. The value of the Poisson's ratio was found to be 

 positive and equal to 0.23 in contrast to Voigt's measured value of —0.51. 

 At high temperatures the dielectric and piezoelectric constants increase 

 and indicate the presence of a transformation point which occurs at a 

 temperature slightly larger than the melting point. A large dipole piezo- 

 electric constant (ratio of lattice distortion to dipole polarization) results 

 for these crystals but the electromechanical coupling factor is small because 

 the dipole polarization is small compared to the electronic and ionic polariza- 

 tion and little of the applied electrical energy goes into orienting the dipoles. 



Paper Capacitors Containing Chlorinated Impregnants. Effects of Sulfur.^' 

 D. A. McLean, L. Egerton, and C. C. Houtz. Sulfur is an effective 

 stabilizer for paper capacitors containing chlorinated aromatics, in the 

 presence of both tin foil and aluminum foil electrodes. Sulfur has unique 

 beneficial effects on power factor which are especially marked when tin 

 foil electrodes are used. The value of R (Equation 4) can be used as an 

 index of ionic conductivity in the impregnating compound. Diagnostic 

 power factor measurements on impregnated paper are best made at low 

 voltages. Electron diffraction studies give results in line with the previously 

 published theory of stabilization. Several previous findings are reaffirmed: 

 (a) the importance of all components of the capacitor in determining its 

 initial properties and aging characteristics, (b) the superiority of kraft 

 paper over linen, and (c) widely different behavior of capacitors employing 

 different electrode metals. 



A New Bridge Photo-Cell Employing a PJwio-Conductive Effect in Silicon. 

 Some Properties of High Purity SiliconP G. K. Teal, J. R. Fisher, and 

 A. W. Treptow. a pure photo-conductive effect was found in pyrolytically 

 deposited and vaporized silicon films. An apparatus is described for 

 making bridge type photo-cells by reaction of silicon tetrachloride and 

 hydrogen gases at ceramic or quartz surfaces at high temperatures. The 

 maximum photo-sensitivity occurs at 8400-8600A with considerable re- 

 sponse in the visible region of the spectrum. The sensitivity of the cell 

 appears about equivalent to that of the selenium bridge and its stability 

 and speed of response are far better. For pyrolytic films on porcelain there 

 are three distinct regions in the conductivity as a function of temperature. 

 At low temperatures the electronic conductivity is given by the expression 



'^ Indus. & Eugg. Cliemislry, Noveni1)er 1946. 

 ^^ Jour. Applied Pliysics, Novcmljcr 1946. 



