465 4819 sup b 523 576 637 63710 sup b 570 570 670 67011 174 239 192 21212 9 31 185 18513 143 256 178 20614 sup b 34 201 179 208______________________________________ sup a same samples as in table iv sup b single charge with screen side adjacent the negatively charged roller table iii shows that the process of charging a web with the apparatus of fig1 produces webs with good filtering efficiencies and excellent filtration qualities in addition table iv shows that the process produces bipolar webs with good charge differentials between the two sides of the web table v lists the conditions and charging results for a variety of webs charged on an apparatus according to fig4 table vi lists the measured surface charge potential for those webs table v______________________________________no sup a filt eff sup b charging voltage sup c filt eff sup d u03b4p q sub f______________________________________15 71 65 23 19 2x 99 956 6 9 1 12016 71 65 21 19 1x 99 950 6 55 1 16017 41 55 25 19 2x 96 278 2 3 1 43118 41 55 25 19 1x 95 525 2 55 1 21819 24 55 25 19 2x 80 35 0 9 1 80820 24 55 25 15 1x 81 90 1 0 1 709______________________________________ sup a 15 and 16 are 3 oz yd sup 2 pp 17 and 18 are 1 oz yd sup 2 pp 19 and 20 are 1 oz yd sup 2 recycled pet sup b before charging sup c kv for wire shell number of chargings sup d after charging table vi______________________________________surface.