The frictional charge of ice of artificially prepared polycrystalline and single crystals was measured.
As a result, the following results were obtained.
1. When the ice of polycrystalline with a constant rubbing point (warmer ice or hot point) was rubbed with the ice rod of single crystal with variable rubbing points (colder ice), the former was electrified positively, although it was warmer.
2. When the ice rod of polycrystal with variable rubbing points (colder ice) was rubbed with the ice rod of single crystal, the former was positively electrified in the beginning of the rubbing experiment. However, when the rubbing was continued, the amount of positive
electric charge of the polycrystal was decreased to near zero, then the sign was reversed to the negative.
3. It was found that after the reverse in sign, the surface structure of the constant rubbing point (warmer ice) in the ice rod of single crystal changed to polycrystalline, and the grain size of the polycrystalline newly produced by rubbing was as small as one tenth of the original polycrystal ice rod prepared. From the observational results it was concluded that the ice of polycrystalline was always electrified positive when it was rubbed with the ice of the single crystal, in spite of temperature difference. The smaller the grain size of polycrystal, the greater the tendency described above.
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