Measurement of a gas by condensation

Many gases (see Appendix 2) have relatively high boiling points so they can easily be liquefied and measured in the liquid form. The gas is passed into a vessel, which is then cooled to the appropriate temperature, as shown in Fig. 7.6. The quantity of condensed gas can be measured by volume or by weight. When the required quantity has been condensed the cylinder is closed and the reaction flask is attached to the safety trap. The cooling bath is then removed and the gas allowed to distil into the reaction vessel. The mercury bubbler and safety trap serve the usual functions. 

A specific quantity of gas can be added to a reaction if the gas is prepared using a chemical reaction of known yield. Methods and apparatus for preparing some commonly used gases are described in Section 7.6 and mention must also be made of an elegant gas generator devised by H.C. Brown, which is described in detail elsewhere.  

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