NOYES AND GOODWIN. — VISCOSITY OP MBUCURY VAPOR. 229 



in measuring the quantities of the different gases which under a constant 

 difference of pressure passed in a given time through the same capillary 

 kept at a definite constant temperature. O. E. Meyer* has derived the 

 following formula for calculating the viscosity coefficient of a gas from 

 its rate of flow through a capillary tube : 



"^ 16 A. joiKi 



where A is the length and R the radius of the tube, t the time, ;3i the 

 pressure at which the gas enters and p2 at which it leaves the tube, and 

 Vi the volume of the transpired gas measured at the pressure p^. In 

 case of comparative experiments made with the same capillary on two 

 different gases, the following proportion holds true : 



Vi '■ V-2 



(pr - p^'h h , {po^- pz-y.h^ (2) 



Wl »2 



in which 7ii, n^, represent respectively the number of gram molecular 

 weights of the two gases transpired, — since n is proportional to the pro- 

 duct p V. 



The apparatus and experimental method that we employed were 

 necessarily quite different from the usual ones, and they will therefore 

 be briefly described. The capillary used in the most complete series 

 of experiments consisted of a glass tube about 74 cm. in length and 

 0.34 mm. in internal diameter (determined by measuring the volume of a 

 known length by means of mercury). A smaller capillary about 49 cm. 

 in length and 0.22 mm. in diameter was used in a preliminary series. 

 The capillary was bent in the manner shown in Figure 1, except that, as 

 actually constructed, it was made much more compact. To its ends were 

 fused pieces of ordinary glass tube, as shown in the figure : one of these 

 was provided at the point A with a ground glass joint. The capillary 

 was placed in a vertical position in a heavy steel cylinder (see A, Fig. 2) 

 30 cm. high, 2.8 cm. internal diameter, having a small orifice at the side, 

 through which the ground joint protruded for a distance of about one 

 centimeter. The capillary was held in position in the orifice by packing 

 with loose asbestos. Although the capillary was vertical, the influence 

 of gravity was eliminated by reason of the fact that the ascending and 

 descending parts were made equal in length. The top of the cylinder 

 was closed by an iron plate screwed down with a nut, N; the nut and 



* Fogg. Ann., CXXVII. 269. 



