Sealing Materials and Lubricants

The choice of sealing materials and lubricants deserves particular consideration, especially since a great number of 

These are principally used for ground joints and stopcocks. Numerous commercial products are available of these, the following are most frequently used  

Ramsay grease has many uses and is commercially available in two forms viscous, chiefly for standard stopcocks and ground joints, and soft, for large stopcocks and ground joints as well as desiccators, and for use at lower temperatures. This lubricant satisfies most of the requirements of preparative laboratory technique and even suffices for high-vacuum work. It can be prepared by mixing paraffin, vaseline and crude rubber (1 3 7 

Silicone grease, which is chemically very resistant, is also recommended to prevent rubber from sticking to glass. Its vapor pressure at room temperature is immeasurably low. It is also serviceable at rather high temperatures. The author has observed that, with this grease, stopcocks that have not been used for a rather long time have a tendency to stick. When warmed, however, they can almost always be readily loosened again. 

Stopcock greases stable to chlorine can be obtained by chlorination of paraffin-stearin mixtures at 150°C and additional treatment with NOCl. The chlorinated mixtures are degassed by heating in vacuum. At higher temperatures perchloronaphthalene may also be used as a lubricant. Apiezon greases are also fairly stable to chlorine, even without preliminary treatment. 

---