Coal carbon electrodes heat treated at temperatures between 1000°C and 2800°C were tested with repetitive electric discharge and pulsed electric discharge. The electrode specimens were prepared from the mixture of Akabira weakly-caking coal and the additional matter (natural graphite and pitch) by means of cold molding of 2000kg/cm². The stability of repetitive discharge is the better at heat treatment temperature (HTT) of about 1400°C and about 2800°C, and the one of pulsed discharge is the best at HTT of about 2800°C. The durability of electrodes increased for the repetitive discharge and decreased for the pulsed discharge with the increase of additional matter. The durability of electrodes for the pulsed discharge showed a maximum at about 15% of additional matter. The coal carbon electrodes, which contain about 10-30% additional matter, heat treated at HTT of about 2800°C had much better electric discharging properties than the commercial arrester carbons.

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As we found equi-centred multi-ringed bodies on each sliding surface of pitch coke brushes under an electron microscope, we tried to trace them to the origin in each manufacturing process and clear up their characteristics. As a consequence, we could confirm that they originated from vortex-like bodies which had been generated in flow layers of coal pitch coke through the coking process, but not in petroleum pitch coke; that these microstructures were formed with equi-centred multi-shells which were composed of fine carbon crystals and ordinary graphite grains in turn, whose orientations of crystalits on each shell were apparently perpendicular. Besides, dropping out traces of shells were observed easily on each polishing and sliding surface of brushes. Considering these structures and the others, then, we could estimate them to be hard or stiff and have high electric resistance.
Trying to investigate how influential the multi-shelled body had been on electric sliding contacts, we could notice that it played a significant role in the brush ability; commutation, damages of a commutator and brush wear, and that variances in brush ability depended upon its distribution on the sliding surface.

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Tar-pitch was carbonized under compression by using autoclave. Coke thus obtained had better coking value and graphitizability than usual cokes. It was assumed that the component which were rich in condensed ring compounds of relatively low molecular weight carbonized without suffering any loss. The coking tests were carried out under various pressures. Nitrogen, hydrogen and oxygen were used to inquire the effect of gases on coking process.

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The decomposition processes of graphite-nitrate and graphite-bisulfate lamellar compounds were found by the X-ray diffraction method to be different from each other. The first stage lamellar compound of graphite-bisulfate decomposed to the mixed stage of the second and third stages, and the further decomposition was observed as a gradual shift of (001) diffraction lines. On the other hand, the second stage lamellar compound of graphitenitrate decomposed to the mixed stage of the third and fourth stages, and then decomposed to the residue compound directly. The third stage itself decomposed to the residue compound directly. There were no intermediate stages between the third or fourth stage lamellar compound and the residue compound. The decomposition of the graphite-bisulfate lamellar compound seemed to be caused from the decrease of the concentration of sulfuric acid by the absorption of water vapor, but the decomposition of graphite-nitrate to be caused from the vaporization of nitric acid.

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