Electrification by being forced through the air of sprayed skim-milk, powdered skim-milk and other foodstuff-powdered whole-milk, powdered butter-milk, powdered lactose and flour-is measured by the gain of potential in their swift movement.
In spraying of skim-milk, charge on most of the particles atomized to about 200μ in diameter is positive while that on larger ones is negative. In pneumatic conveying of powdered skim-milk through duct, amount of positive charge on particles incleases with their concentration in air and the velocity of air stream.
Concerning those foodstuff that were examined, amount of charge on powder particles of less than about 25μ in diameter increases with their surface area, but for larger particles, it is the volume rather than the surface that determines the increase. Powder particles except those of lactose are almost charged positive if they are small, but negative if large. Particles larger than about 80μ in diameter have no polarity. Charge per particle ranged 0.394×10-4-_??_4.142×10-4 e. s. u., and mean density of charge 0.881.85 e. s. u. /cm2.
