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Electricity due to air-blown particles
698
CURRFNT TOPICS.
[J. F. I.
Electricity Due to Air-blown Particles. P. E. SrIAW. (Proc. "Electric charges due to mutual impact of dust or other particles arise in various ways: (a) electric dust- or sandstorms in the Tropics; (b) electric snow storms in the Antarctic; (c) electric flashes seen in the ejectamenta from volcanoes; and (d) electric charges, and possibly sparking, brought about by the raising of organic powders in certain industrial processes." It is the impact of like particles that produces such electrical charges, though it has been customary to hold unlike substances as necessary for the production of electricity by shock. A few years ago the author showed " t h a t identical solid surfaces can charge one another by friction or impact, and, further, that this property of the surface changes as rubbing continues. It was there shown that such organic insulators as ebonite and celluloid yield considerable charges, whereas hard inorganic materials such as quartz, calcite and glass, produce smaller effects. When the 'like' solids meet in violent impact, not rubbing, the combined net charge is not nil, as might be expected according to Faraday's law of equal and opposite frictional charges, but finite, generally negative; so that the air surrounding the surfaces must attain an equal positive charge." In the series of experiments here described measurements were made with an electroscope on the potential developed by blowing with a speed of 54 miles per hour successive charges of particles, each .15 c.c. in volume, through a tube into a vessel, both tube and vessel being lined with the same substance. When both were lined with copper the charge developed on the vessel decreased progressively from + .o4 to -- .27 electrostatic units as the driven particles were successively Cu, Fe, Brass, Zn. When both were lined with zinc a similar decrease from + .98 to + .14 E.S.U. was noted as the particles passed through the same change from Cu to Zn. The electrical charges on the solid particles are usually considerably larger than those on the air, but this is not so when copper meets copper or zinc meets zinc. Sand on sand causes very large charges on the grains, as well as on the sand-lined container. The development of electricity is enhanced by having all surfaces clean, by raising the temperature of the blast and, by increasing the velocity of the blast. Even when the two surfaces brought into sharp contact are chemically alike electrical charges are produced by impact. G.F.S.
Roy. Soc., A 789.)
CURRFNT TOPICS.
[J. F. I.
Electricity Due to Air-blown Particles. P. E. SrIAW. (Proc. "Electric charges due to mutual impact of dust or other particles arise in various ways: (a) electric dust- or sandstorms in the Tropics; (b) electric snow storms in the Antarctic; (c) electric flashes seen in the ejectamenta from volcanoes; and (d) electric charges, and possibly sparking, brought about by the raising of organic powders in certain industrial processes." It is the impact of like particles that produces such electrical charges, though it has been customary to hold unlike substances as necessary for the production of electricity by shock. A few years ago the author showed " t h a t identical solid surfaces can charge one another by friction or impact, and, further, that this property of the surface changes as rubbing continues. It was there shown that such organic insulators as ebonite and celluloid yield considerable charges, whereas hard inorganic materials such as quartz, calcite and glass, produce smaller effects. When the 'like' solids meet in violent impact, not rubbing, the combined net charge is not nil, as might be expected according to Faraday's law of equal and opposite frictional charges, but finite, generally negative; so that the air surrounding the surfaces must attain an equal positive charge." In the series of experiments here described measurements were made with an electroscope on the potential developed by blowing with a speed of 54 miles per hour successive charges of particles, each .15 c.c. in volume, through a tube into a vessel, both tube and vessel being lined with the same substance. When both were lined with copper the charge developed on the vessel decreased progressively from + .o4 to -- .27 electrostatic units as the driven particles were successively Cu, Fe, Brass, Zn. When both were lined with zinc a similar decrease from + .98 to + .14 E.S.U. was noted as the particles passed through the same change from Cu to Zn. The electrical charges on the solid particles are usually considerably larger than those on the air, but this is not so when copper meets copper or zinc meets zinc. Sand on sand causes very large charges on the grains, as well as on the sand-lined container. The development of electricity is enhanced by having all surfaces clean, by raising the temperature of the blast and, by increasing the velocity of the blast. Even when the two surfaces brought into sharp contact are chemically alike electrical charges are produced by impact. G.F.S.
Roy. Soc., A 789.)