Greasing glass joints

It is often advisable to lubricate ground-glass joint surfaces with an extremely thin film of vaseline. This applies particularly to joints employed in assemblies for distillation under reduced pressure. For distillations under greatly reduced pressures or at very high temperatures it is essential to employ a special lubricant, e.g., silicone grease. 

Some simple apparatus, suitable for high vacuum distillation, are collected in Figs. 11, 26, 1-4. Fig. 11, 26, 1 represents an apparatus, which is particularly well adapted for solids the ground glass joint must be lubricated with a grease of negligible vapour pressure. Hickman s vacuum still is shown in Fig. 11, 26, 2 it is about 60 mm. in diameter. 

Kel-F grease is recommended for ground-glass joints. Nitronium tetrafluoroborate slowly attacks silicone stopcock grease, causing air to enter the flask. 

The apparatus is set up as illustrated in Fig. 12. The use of a reaction flask and condensers fitted with ball-and-socket joints increases the flexibility of the apparatus and reduces the chance of air entering the system through improperly set joints. The ground-glass joints are greased and held in place with well-tightened ball-and-socket-joint clamps. 

Whenever apparatus with ground glass joints is used, Dow silicone grease provides excellent lubrication and airtight seal. 

The checkers recommend the use of silicone grease on all glass joints. 

Ground glass joints were connected using Teflon sleeves or a chlorofluorocarbon stopcock grease. 

Equipment. All manipulations were performed under inert atmosphere conditions. Standard vacuum line and inert atmosphere techniques were employed.5 Reactions were conducted using glassware with solvseal joints. Glassware with ground glass joints could not be used as these joints were prone to leak at low temperature or when solvent dissolved the vaccum grease. 

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