An Inexpensive Check Valve of Oil Bubblers
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There are commercially available valves for protecting nitrogen manifolds from oil backing up from the bubbler due to reduced pressure in the line. These valves are designed with a three-way stopcock so that one can intentionallv ~ D D ~vacuum V and refill the manlfold wrth nitrogen ("rapid purging"),
and costs only pennies. The set-up is shown in the accompanying figure. The only modifications from a normal homemade bubbler are the flaring of the tip of the glass tube, which then has inserted into it a l-ml polystyrene centrifuge tuhe, such as a Fisher 04-978-145 (60),readily available from your local biochemist. We made ours from 8-mm glass tubing (ad.) flared to 12 mm at the bottom. A couple of tries will usually give a flare whieh makes a pretty good seal on the centrifuge tuhe. A glass lathe helps tremendously. The assembly was inserted in a 25 x 200 side a m test tube, whieh allows for vigorous bubbling without overflow. The seal is not perfect but prevents backup even under aspirator pressure until nitrogen can refill the manifold. We use the bubblers as shown, hut if rapid purging is desired, a three-way stopcoek anywhere in the manifold will allow this.
I. David Reingold Middlebury College Middlebury. VT 05753 Theodore G. Lindernan The Colorado College Colorado Springs, CO 80903
Volume 61
Number 8
August 1984
739
