The McLeod compression manometer

The principle of this manometer, which gives a reliable reading only for permanent gases, is the compression of a certain volume of the gas, measured at the pressure to be determined, to a small volume in a capillary tube. The gas sample is in this way brought to a higher pressure that can readily be measured. The pressure p of the original gas can then be calculated with sufficient accuracy by means of the formula 

Ah = the pressure at which the compressed gas is finally measured (the difference in mercury level in mm), 

Fj = the volume of sphere G and capillary tube K (measured from the junction at R), Fj = the volume of the compressed gas in capillary tube K. 

Volume of sphere and required amount of mercury in commercial McLeod gauges 

The numerous modifications of the McLeod manometer are dealt with in Ebert s book [51]. A pneumatically controlled model with automatic setting which is independent of the atmospheric pressure is described in detail by Peche [52]. A number of recommendations are made which are intended to ensure reproducible measurements. 

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