Temperature on the Viscosity of Gases. 207 



Peoceduke in Measueements. 



The first operation is thoroughly to dry the apparatus and 

 fill it with pure dry gas. This was accomplished by repeated 

 exhaustion and refilling of all necessary parts of the tubing, 

 gauges, &c, none but thoroughly dry gas being admitted. 

 This operation was repeated on each separate day of measure- 

 ment, so that any error from slight leakage or diffusion of 

 either air or moisture should be avoided. On the first intro- 

 duction of the dry air or carbonic acid, the further precaution 

 was taken to run the apparatus under quite high exhaustion 

 for many hours consecutively ; and in all cases, on each day 

 of measurement, the apparatus was run for an hour or more 

 before any readings were taken. 



The procedure in measurement was as follows : — The aspi- 

 rator was set in operation, J being full of the gas. The 

 generator and purifiers were connected at P, and the cock c 

 opened, /remaining closed, so that the supply of gas came 

 from the generator ; the temperature of D C was regulated, 

 the stirrer being in continuous operation ; the ice-bath was 

 placed round ^L Z?, the regulator at iVadjusted, and the trans- 

 piration allowed to proceed until the gauges E and F were 

 nearly stationary. Then c was closed, and /opened and ad- 

 justed so that the reading of R slowly increased, whereupon 

 c was again opened for the slow escape of the gas and the 

 maintenance of a constant initial pressure p x . The transpi- 

 ration was allowed to proceed until E, F, and R were suffi- 

 ciently near stationary, when readings of the mercury columns 

 by the cathetometer and of the thermometers were taken 

 systematically. After a complete set of readings had been 

 thus obtained, the apparatus was thoroughly inspected and a 

 second set made ; and so on until the number was deemed 

 sufficient, whereupon the temperature of D C was changed or 

 the pressure modified as desired. The results thus obtained 

 furnished, on reduction, the values of p h p 2 , p s , and t for the 

 computation of the ratio of the coefficient of viscosity at the 

 higher temperature to that at 0° 0.; the further requirements 



being the constants ^ * =K for the tubes, R x and X 1} R 2 and 



-til A-2 



X 2 being the radius and length respectively of the tubes A B 

 and CD, as shown at page 209. This value of K was found 

 from measurements similar in all respects to those just 

 described, except that the tubes AB and CD were both 

 surrounded with ice at the same time. 



The apparatus was also arranged to place D C in steam. 

 When left at night for subsequent use, an outward pressure 

 was created in all parts of the apparatus. 



