The fact that the registration of wet and dry gas-meters often varies even when an equal volume of gas being passed has been known for a long time, and the author endeavoured to discover predominating causes through theory and experiments. The cause of variation for each sort of gas-meter was first assumed : for a wet gas-meter it is the change of the capacity of measuring chambers of a drum when pressure difference at the inlet and the outlet sides or the rate of flow of gas changes, and for dry gas-meter the variation of leakage of gas through microscopic clearance between sliding surfaces of the slide valve-covers and-seats when the pressure difference of the two sides and the viscosity of gas change, and the author derived an equation, for each sort of meter, showing error of registration as the function of rate of flow of gas. In carrying out a number of experiments on both wet and dry gas-meters, verification of the equations was made with the consequence that they were fairly well in agreement. The author is, therefore, of the opinion that the equations derived took account of the predominating causes of the variable registration of the instruments and emphasizes that it varies systematically. Lastly, a number of scientific information and hints based on the theory is suggested which might be usefull in respect to the improvement in either the making or using gas-meters.
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