A SIMPLE ASPIRATOR TRAP EDWARD F. DEGERING, PURDUEUNIVERSITY, LAPAYETTE, INDIANA The accompanying figure shows a simple, easily constructed, and dependable aspirator trap. In most laboratories where aspirator filter pumps are in use, the fluctuations in the water pressure are usually great enough to cause a pump to "suck back," often resulting in a mined procedure. While the new aspirator pumps are usually equipped with a check valve, these valves soon become corroded and fail to work, hence are not entirely satisfactory unless the check valves are replaced periodically. A trap constructed as indicated in the drawing, is dependable even under extreme fluctuations in the water pressure, and there are no parts to wear out. If necessary, the mercury may be cleaned as usage requires. If the outlet from the mercury trap is placed exactly opposite the inlet tube just above the surface of the mercury, as shown in the drawing, there is no hazard of sucking the mercury into the aspirator pump. However, the lower end of the outlet tube should be open and dip below the surface of the mercury, and the bore af the tube should be about 7 mm., so To ~ ~ that Iprercury ~ i particles ~ spattered ~ into t the ~ outlet will fall back to the mercury trap. The calcium chloride tube serves as a moisture trap, not entirely necessary, which may be drained as needed. The inlet tube to the mercury trap should dip just far enough below the surface of the mercury to insure a column of mercury in the tube capable of balancing the vacuum obtainable. If the bore of the inlet tube is 2 to 3 mm., the inlet tube should extend about 5 to 10 mm. below the surface of the mercury. The only experimental disadvantage encountered in the use of such a trap is the decreased efficiency of the pump, due to the 5 to 10 mm. of mercury through which the vapors must be drawn. But the slight decrease in vacuum is negligible compared to the usefulness, permanence, and dependability of a properly constructed trap of this type.
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