In the Laboratory edited by
Cost-Effective Teacher
Harold H. Harris University of Missouri—St. Louis St. Louis, MO 63121
Inexpensive Pipet or Buret Jar and Washer
Henry Brouwer Department of Chemistry, Redeemer College, Ancaster, ON L9K 1J4, Canada;
[email protected] Clean glassware is essential if students are to do analytical work in the laboratory, but without proper soaking and washing equipment it is difficult to keep pipets and burets clean. Commercially available pipet jars and washers can easily cost several hundred dollars, money that instructors could spend on other equipment. In this communication, I describe a method of constructing a pipet or buret jar and washer from supplies available at the local plumbing store. A 10-foot length of white PVC sewer pipe (either 4- or 6-in.) together with four end caps, a 10-foot length of 1⁄2-in. CPVC water pipe with eight 1⁄2-in. elbows (four street elbows [male and female ends] and four regular elbows [all female ends]), and PVC and CPVC adhesives are all that is required to construct two jars and washers, one shorter set suitable for pipets and a taller set suitable for burets. To construct the jars, cut the sewer pipe to the appropriate length (the pipe should be about 5 cm longer than the longest pipet or buret) and glue the end cap to one end of the pipe. (Coat both the outside of the pipe and the inside of the cap with plenty of adhesive before attaching the end cap to the pipe.) Fill the jars with water to test for leaks. To construct the washer, attach a siphon tube to the side of one of the jars as follows (see Fig. 1). Drill a 5⁄8-in. hole through the side just above the bottom of the jar (the hole will go through both the end cap and the pipe). Coat the inside of this hole liberally with PVC adhesive. Next coat the male end of a CPVC street elbow (A on diagram) with CPVC adhesive and press firmly into the hole with the elbow pointing up. Construct the siphon tube of two lengths of 1⁄2-in. CPVC pipe joined at the top with two elbows (one of each type); the length should be such that the top of the siphon tube will be about 2.5 to 3 cm below the top of the washer. Glue one end into the female end of elbow at the base of the tube. To the other end, attach an elbow (B on diagram) with a short length of pipe (about 4 cm); slip a 30– 40-cm length of 1⁄2-in. i.d. plastic tubing over this pipe to drain the water into the sink. For extra support, glue the siphon tube to the side of the pipe at the upper and lower ends by dabbing adhesive between the two and holding the tube firmly in place while the glue dries. Place dirty pipets or burets (with the tips up) in the appropriate jar filled with a solution of glassware detergent for at least a day. To rinse, transfer the pipets or burets to the washer. Bend a short length of glass tube into a U-shape and
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Glass tube To water supply
1/2" CPVC pipe
4" PVC pipe
End cap
A
B
To drain
Figure 1. Diagram of buret washer.
connect to one end of a plastic tube attached to a water tap; hang the glass U-tube over the top edge of the washer. The end of the siphon drain should be as low as possible in the sink (this will affect the rate at which the washer empties). Turn on the water supply; once the jar is almost filled, adjust the flow of water so that the water will automatically siphon out but not so fast that the washer will not empty. Leave the water at that flow rate. After rinsing for several hours, the washer may be drained and filled once with deionized water to give the glassware a final rinse. For a small number of pipets or burets, the 4-in. pipe will be adequate (it can hold about 12 burets). For larger quantities, the 6-in. pipe would be more suitable. For greater ease of transferring the pipets and burets, construct a basket from the 4-in. pipe fitted with a cap with holes drilled in the bottom; small pieces of pipe glued to the bottom provide space for the water to flow freely in and out. This basket, of course, will only work with the larger washer or jar (I have not been able to find a pipe of suitable diameter to make a basket that just fits inside either size pipe). Attach the soaking jar and washer to a suitable support to prevent them from being knocked over accidentally.
Journal of Chemical Education • Vol. 77 No. 2 February 2000 • JChemEd.chem.wisc.edu
