Buoyancy Correction for Air, Its Method and Limit in Precise Laboratory Weighing

Abstract

A new method presented in the paper is exact and convenient in correcting the observed values of mass of objects for air buoyancy in laboratory weighing. The extent of accuracy one must know of the densities of air, object and weights are found on nomographs from the approximate density value. Another nomograph gives the value of air buoyancy correction factor k from density values of 2_??_3 significant figures. With this nomograph, which is different from the case of conventional tables, k can be found for almost all combinations of object and weights. For a more accurate correction, one must know more accurate values of density, the density of air in particular, and in such a case, k is calculated by a theoretical equation. The density of air depends on various factors. In the usual method, in which the density is calculated from factors P, T and composition of air, 3±10^-4 is concluded to be the limit of accuracy. Multilayer adsorption of water vapor also affects the weighing accuracy. The density or mass allowed for the tare of a weighing vessel can also be de-termined from the nomographs. Among the balances of various types, the balance of gravity type is most suited to precise weighing.