Document MGz0j28Rne2gjEpDOxrXEL8O7

202 INDUSTRIAL HYGIENE AND OCCUPATIONAL MEDICINE These results show that all four instruments collected essentially equal amounts of material. This was to be expected, since the precipitating potential and air flows were maintained as nearly equal as possible. Any difference in the amount of material collected is believed due to unavoid able variations in the air flow or voltage. EFFECT OF POLARITY A further series of tests were made to determine the effect of polarity on the amount of material collected. Two PHS-SO's were used, one operated positive and the other negative, and these were tested simultaneously with the PS-10, which was positive in some tests and negative in others. The tests were conducted under the same conditions as described previously. The results are shown in table 2. The negative corona appears much brighter to the eye than the positive, and the conclusion might be drawn that the negative corona effects better precipitation. This supposition was not borne out by the limited data obtained. Table 2.--Comparison of Material Collected with Positive and Negative Polarity Test 1 2 3 4 Totals.. 5 6 7 Totals.. 8 9 Totals.. Material Used lead oxide Load oxide Lead oxide Lead oxide Weight of Material Collected, , Mg., with Indicated Instrument Sampling Volume and Polarity of Center Electrode Operating Rate, Sampling of Air -------------------------------*----------------------- Voltage, Cu. Ft. Time, Sampled, PHS-50 PHS-50 PS-10 PS-10 Kv. per Mia. Min. Cu. Ft. Pos. Neg. Neg. Pos. . ..13.5 3 60 180 46.3 45.7 47.4 4 13.6 3 60 180 30.0 29.4 30.4 .... 13.7 3 30 90 46.6 47.1 45.6 13.8 3 30 90 18.2 18.9 18.4 180 540 141.1 141.1 151.8 Lead oxide 13.5 3 30 90 27.9 25.8 Lead oxide 13.5 3 45 135 33.5 29.3 Lead oxide 13.5 3 15 45 4.3 3.4 27.7 34.1 4.2 '80 270 . 65.7 58.5 66.0 Chromate dust 13.5 3 45 135 37.2 39.9 39.1 Chromate dust 13.5 3 30 90 19.1 19.0 19.8 75 225 56.3 58.9 58.9 .... SUMMARY A new power supply using radio frequency has been described which will fit in the old M. S. A. case. This power supply weighs only 2^ lb. (1.24 Kg.) and can be constructed for about $35. Laboratory tests showed collection efficiencies comparable to those of other instruments now in use. Lead and zinc oxide fume and a residue dust from a chromate plant were used for these tests. A limited number of tests showed no essential difference in collection efficiency when the polarity was reversed. The ^instrument has not been subjected to field tests but was operated in the laboratory for over 150 hours, including 8 hours a day for four consecutive days. There was no indication of any breakdown of parts during this time. APPENDIX LIST OF PARTS FOR PHS-50 POWER SUPPLY 1--15 kv. radio frequency coil (Spellman Television Company, Inc., 3029 Webster Ave., New York 67) 1--R. F. filament transformer (Spellman) v , 1--1B3GT tube 1--6L6G 1--Ceramic octal socket 1--Bakelite octal socket