Abstract: A plurality of bags filled with a product, which bags are to be stacked one upon the other so that the adjacent surfaces of the bags are pressed together by the weight of the upper bags pressing downwardly thereon, are coated with a coating means for controlling the friction between the coating means and the coextensive supporting surface of the adjacent bag. The coating means is adapted to become increasingly adhesive and cohesive when subjected to pressure, but with the cohesion and adhesion decreasing upon removal of the pressure so that the cohesion and adhesion between the supporting surfaces of the top two bags in the stack and the cohesion and adhesion between each pair of coextensive supporting surfaces is greater than the next pair above it by virtue of the increased weight of the product and the bag between them. As a result, the removal of the top bag in the stack produces a decrease in the cohesion and adhesion between the remaining bags in the stack.

Abstract: A method of an apparatus for improving the capacity and efficiency of electrostatic precipitators by increasing the average field intensity. The precipitator is supplied with a substantially constant base level DC voltage that is less than the sparking threshold level of the precipitator, and superimposed thereon is a periodic DC voltage waveform of short duration having peak levels that substantially exceed the sparking threshold level. By controlling the characteristics of the periodic DC voltage waveform the average applied voltage is greater than the sparking voltage but the duration of the instantaneously applied voltage is not sufficient to cause sparking in the precipitator.