Abstract
The electric charge has been measured, and its polarity observed, in each particle of powder under the condition of about 65 per cent R.H. and the pressure of saturated vapour when friction takes place as factor of the electric charge among the powder particles that are channeled through the chute net, and in the measurement is used the method requiring alternating current as shown in Fig. 1. Four kinds of powder, polyvinyl chloride, mica, potato-starch and lactose were used for the experiment.
Under about 65 per cent R.H. both polyvinyl chloride and mica produce 60 to 80 per cent of negatively charged particles in number as shown in Figs. 10, 11, while both potato-starch and lactose hold the same per cent in negatively and positively charged particles and produce the reversal of polarity which turns negative from positive in the boundary of range 50 or 60 microns in diameter as shown in Figs. 12, 13. In general, the distribution of positively and negatively charged particles has the following relations to the size of particles. The amount of charge on powder particles of less than about 70 microns in diameter increases with the surface area of the particle as shown in Figs. 2∼5. For particles larger than about 70 microns, it is in proportion to the volume. But the charge of powder particles larger than about 100 microns in diameter tends to be neutral.
Under the condition of saturated vapour the amount of charge which is proportional to the volume of particle disappears especially in mica and lactose as shown in Figs. 6∼9.
