All stopcocks and movable joints in a high vacuum system must be satisfactorily lubricated, yet leak proof. The lubricant for such joints must not contribute to the pressure within the system and must be of extremely low vapor pressure at the temperature of operation. Also the lubricant must be stable, chemically inert, non toxic, easily applied and preferably easily removed when desired. Finally, the lubricant must lubricate, an obvious statement but a necessary one since so many so-called high vacuum lubricants have in fact very poor lubrication properties.
All these desirable properties are found in Apiezon greases. As with the oils, a range is offered to enable the right grease to be chosen for the job at hand. It has not been found possible to produce a high vacuum grease which is both multigrade and a good lubricant at all temperatures. The closest approach to such a multigrade grease is Apiezon Grease H which may be used over a relatively wide range of temperatures.