On a method of determining the viscosity of gases, especially those available only in small quantities

Abstract

The apparatus about to be described was designed for the purpose of comparing the viscosities of neon, xenon, and krypton—the loan of which Sir William Ramsay kindly offered the author—with that of air. With such small quantities of gas available, the volume content of the apparatus must obviously be correspondingly small, and therefore, it would seem, unsuitable for absolute measurements. The object of the present paper is to show that this is by no means the case. As will be seen later, the method is actually restricted to small quantities by the conditions of the experiments, but there is no reason why it should not be used even when the gas under test may be obtained in practically unlimited amount. Theory of the Method . Consider a closed glass vessel (as in fig. 1) consisting of two connected limbs, one a fine capillary tube and the other of much greater cross-sectional area, yet sufficiently narrow for a pellet of mercury to remain intact in it. Let V be the volume unoccupied by mercury (the volume of the capillary tube being considered negligible). Let P denote the steady pressure of the gas in the tube when the latter is held horizontally, and let p be the difference of pressure caused by the mercury pellet when the apparatus is vertical. Let p 1 be the pressure and v 1 the volume at any time above the mercury, and p 2 , v 2 , the corresponding quantities below the mercury. Then V = v 1 + v 2 , and p 2 - p 1 = p .