MERCURY SEAL **)

In some cases, the entry into a vacuum system of vapors of materials used for lubricating stopcocks is undesirable.

Sometimes attempts are made to avoid also the absorption by lubricating substances of gases or vapors filling the system being evacuated.

) H. M. Stanier, J. Scient. Instr. 29**, No. 5 (1952).

In these cases, mercury seals are used instead of glass stopcocks. In ordinary mercury seals, however, there are large columns of mercury, which is inconvenient in operation.

The seal described by the authors of this article has the positive qualities of normal stopcocks and at the same time guarantees against vapors of lubricants entering the evacuated system.

Fig. 2.

The axis of such a stopcock must be inclined so that, when the plug is turned through 180°, opening \(A\) is below the surface of the mercury poured into the socket of the stopcock. In this position the high-vacuum side \(B\) is isolated from side \(Б\), which leads to the low-vacuum part of the installation.

The plug and the stopcock are fitted so that the mercury is not forced through between them when side \(B\) is at atmospheric pressure.

Mercury introduced into the upper part of the plug through a small opening in its handle enters groove \(Г\) through the corresponding openings, thus forming an annular mercury seal. This seal isolates the system from the grease coating the plug above \(Г\), and protects it against the inflow of air from outside.

V. V. Fedorov