A digital indicating null method vibrating probe electrometer for electrophotography has been developed. Nulification is made automatically by the aid of the servo techniques. Compensating voltage is supplied from electronically stabilized voltage source, so that high accuracy and high stability of about ±0.2%, on potential measurement is attained.
A coded disk analogue to digital converter connected with nullifying potentiometer encodes the angle of rotation to three decimal numbers and indicates the surface potential of the electrophotographic materials in digital numbers in the range of 0 to-999 volts.
The exposure lamp is 50 watt exciter lamp, its color temperature is adjusted at 2854°K and maximum intensity obtainable is about 500 lux. The exposure intensity is controlled with an optical neutral filter.
The sector type of electromagnetic shutter controlled by a crystal controlled digital timer gives accurate exposure.

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In the first paper of the series, a report was made on tone rendering of images on Electrofax papers obtained by contact printing with halftone positives.
The object of this work is to test tone reproductions on Electrofax papers by screening with a contact screen. This is a method of forming halftone images from continuous tone originals.
In this work, two gray and a magenta contact screens are used. The dot density of the gray and the magenta contact screens are shown in Fig. 1. Fig. 2 shows the spectrophotometric transmittance of the magenta screen. Fig. 6 shows D versus Log E curve of tested papers. Spectrophotometric reflectance and spectrogram of tested papers are shown in Fig. 8 and Fig. 9-A.
Tone reproduction curves with gray screens G1 and G2 are shown in Fig. 10 and 11. From those curves it is found that the reproduced tones correlate with the contrast of screen dots. Tone reproduction curve with magenta scfeen M1 are shown in Fig. 12. Fig. 13 shows the tone reproduction curves for the effect of filter changes on paper P with the screen M1. Using paper P, we have significant variations of tones and so it may be used in practice.
Kodak Wratten filter No. 30, No. 33, No. 4 and No. 44A are used and their spectrophotometric transmittance are shown in Fig. 4. Fig. 9-B shows the spectrograms when filters mentioned above are inserted before the light source. Table 2 shows the exposure ratio of screening.
Through out this work, a 100V-1 KW tungsten lamp is used. Fog is removed with the carrier brush and to prevent discharge effect, a sheet of Myler is inserted between the charged layer and the material contacted directly.
In this work, halftone images obtained with contact screens are for final prints, but not to use for printing process.

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A study was made of organic photo conductors patented by Kalle Co. Thirty three kinds of organic compounds were synthesized and their light decay characteristics, sensitivity and electrophotographic image were measured. From the results the relationship between chemical structure of organic photoconductors and electrophotographic characteristics was discussed.

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The charge spectrometer device is outlined and the following equations for calculating particle charge from deflection of aerosol beam in the charge spectrometer are presented; equations of Lipscomb, of Cornish, of Boussinesq, and of the Authors. The method for obtaining particle size by using charge spectrometer is also described.

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The charge of tobacco or mosquito incense aerosol which was charged by corona discharging device or by illumination with ultra violet ray was measured by a chage spectrometer. The corona discharging was positlve corona. Measurements were performed by reading the deffection of aerosol beam under various electric fields in the charge spectrometer. The mechanism of charging of aerosol in the corona discharging process was discussed and the equation for estimating charge of aerosol which entered to the charge spectrometer through corona discharglng tube was derived. The charge calculated from the above equation was compared with the charge obtained by using all equations of Lipscomb, Cornish, Bonsinesq, and the authors. It was found that the tobacoo aerosol was initially negative but it changed to prsitive in passing through the positive corona field or by illuminated with ultra violet ray. The charge of mosqite incense aerosol was also positlve in passing through the positive corona field. The results of size measurement of these aerosol by charge spectrometer was not agreed with that obtained by a ultramicrosopic method. The formner was larger than the latter.

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A study was carried out to ascertain whether it was possible to obtain powder images fully available in making original prints for plate making on litho-film bases by means of electrophotographic transferring.
First, a test chart was printed contactly on Electrofax paper, with corona discharged. Then after developing with a magnetic brush to obtain original prints for transferring, the image of the test chart was transferred to on film bases or papers by means of electrostatic transferring and the other by adhesive. The results were examined on their respective density and resolving power to see their practicability for original prints for plate making.
The transferring effect on the film bases was found to be less than that on the art paper, but when adhesive was used, its effect was recognizable to the greater excellent. About the method on film base, a sufficient density in the powder image could not be obtained, but through fixing treatment it was brought within the range of possibility for plate making . Resolving power was different with various transferring methods: 12. 5 lines/mm by the electrostatic method and 16 lines/mm by one using adhesive were obtained.

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