NOVEMBER, 1950
0
STEAM-HEATED ACID CLEANING BATH C. K. HANCOCK The A. and M.College of Texas, College Station, Texas
Two steam-heated cleaning baths, constructed as shown in the figure, have been in satisfactory use in this laboratory for two years. A glazed, 3-gallon crock, to contain the dichromate-sulfuric acid mixture, is set in a glazed, 5gallon crock as a safety measure. The hazard offered by the improbable simultaneous breakage of both crocks seems negligible, and, in view of the low cost and ready availability of such containers, their use appears just,& fied. A similar safety arrangement, involving an inner Pyrex jar and an outer enameled pot, has been described by Moos.' The fivegallon crock is set in a square lead (0.06 inch thick) box with one-inch sides. This assembly is support,ed by a strong wooden box of proper height such that the top of the five-gallon crock is level with the top of the sink wall. A detachable lead trough laid across the top of the five-gallon crock and t,he top of the sink wall prevents the spilling of cleaning solution while transferring glassware from the bath to the sink. The cleaning solution in the bath is heated and kept hot by passing steam throngh the single-turn coil of lead tubing (0.25 inch inside diameter, 0.125 inch mall thickness) and exhausting to the sink. This simple coil, easily shaped by hand to fit the bath, is designed to accomplish satisfactory heating without sacrificing excessive available space in the bath. A slow input of steam maintains the bath temperature a t 70-90°C. When not in use, the five-gallon crock is covered with a transite lid which is notched to fit around the ver-
' Moos, G. E., J. CHEM.EDUC.,23,465 (1946).
tical sections of the lead tubing. I I After two years of intermittent use, the portions of lead tubing exposed to the hot cleaning solution have undergone no appreciable loss by chemical erosion. Originally, a similar coil of Pyrex tubing was employed to heat the bath, but this practice was soon discontinued because of the hazard offered by possible fracture of the Pyrex tubing while passing steam through it. Before the lead tubing coil was tried, sterteam-~eated cleaning~ = t h erosion tests showed a 0.25 per cent loss in weight of a 354 g. lead coupon (0.06 inch thick) after six days of immersion in hot dichromate-sulfuric acid cleaning mixture, and an additional 0.08 per cent loss in weight after six more days of immersion in the hot mixture. These data indioate that after an initial small loss in weight the lead is fairly resistant to further chemical erosion. ,Em
