Working with Exclusion of Oxygen and Moisture

When conducting a reaction or distillation under a continuous flow of nitrogen or argon rather than in a closed system, a suitable outlet valve must be used in order to prevent back-diffusion of oxygen into the apparatus from the surrounding air. In the simplest cases, it is sufficient to use a Bunsen valve (a rubber tube with two lengthwise slits, closed at one end with a glass rod), or a paraffin oil valve. 

If small volume experiments are carried out under exclusion of oxygen, an approved method is to use a balloon filled with inert gas attached to an otherwise closed apparatus. Likewise, using a balloon can easily compensate for changes in 

When working with spontaneously inflammable substances (e.g., organometallic compounds) or with reactions on a larger scale, where there are rapid changes of pressure, it is advantageous to employ a backstop valve. 

Agents for the drying of hquids must, of course, be chemically inert, as otherwise undesired side reactions could occur (e.g., styrene polymerizes explosively on contact with concentrated sulfuric acid at room temperature). 

Suitable drying agents are, for example, calcium chloride, silica gel, molecular sieves, calcium hydride, or phosphoms pentoxide however, their use must be adapted to the requirements and conditions of each polymerization. 

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