Kenneth E. Collins
SUNY at Buffalo Buffalo, New York 14214
A Convenient Glass-to-Glass Connector
Ground glass standard taper joints and hall-and-socket joints are reasonably satisfactory for coupling laboratory glassware for vacuum applications, but they do have several disadvantages. I n the larger sizes, these joints are expensive, difficult to separate, messy to handle and (particularly the ball-and-socket joints) do not consistently give vacuum-tight connections. Several commercial glass-to-glass O-ring joints are now available which are preferable to the conventional standard taper or ball-and-socket joints for many vacuum line applications, particularly in the larger diameter sizes. However, these joints are also costly and may require considerable care in alignment of components to get satisfactory high vacuum service. We describe here two modifications of a glass-to-glass O-ring coupling design' which can be made easily and cheaply in the laboratory by anyone having some experience in the working of glass. Although these couplings may not be suitable for very high vacuum use, (i.e., better than lo4 torr) they are quite satisfactory for use in the medium high vacuum (10-3-10-5 tom)% range. Figure 1 shows two modifications of an O-ring coupling design which can he constructed fromappropriately 'This design can readily he adapted for use in situations requiring @;less-to-metal couplings, or even metal-to-metal couplings. A 4-em diameter O-ring eoupling system of the type described in this paper (see Fig. 3) has a leak rate of less than 1 0 F atm ml secrLcm-I at 10-"err. For vacuum service in the range of 1 0 F torr or better, the Oring should be lightly greased. This can be done by covering the surface of the O-ring with high vacuum stopcock grease, then wipingoff excess grease with lint-free tissue.
0.
b
Figure 1. Two modiflcotionr of the boric O-ring coupling design.
Figure 2. Sublimation system in. rorpomting O-ring coupling.
sized glass tubing and O-rings which fit snugly (with but little stretching) over the inner tuhe. The two modifications differ only in the shape of the inner part. Shape l(a) is somewhat to be preferred when glass tubes of equal diameter are to be joined or when a large diameter tubing section is to he coupled to one of substantially smaller diameter. However, shape l(b) is easier to construct: that is, it is easier to shape the inner piece of l(b) to obtain an optimum confinement or "fit" for the sealing O-ring than is the case for shape 1(a). The projection of the inner section into the outer section and the raised "bumps" along the bottom edge of the inner sections of both designs permit a reasonable degree of rigidity, preventing undesirable wobble of the coupled sections. Two useful applications of these O-ring couplings are shown in Figures 2 and 3. The sublimation cell, Figure 2, is most convenient for routine sublimations of small (
