79 



VISCOSITY OF GASES 



193 



The values also deduced by Kundt and Warburg 1 

 from oscillation experiments at 15 C. differ from the former 

 by nothing more than can be explained by the change of 

 temperature. 



With these numbers the values are in good agreement 

 which Puluj 3 and 0. Schumann 4 have deduced from 

 their observations. I must, however, abstain from citing 

 here all the determinations that have been made, but will 

 mention those measures that concern the newly discovered 

 gases argon and helium, and that have been made with the 

 vapour of mercury. 



The transpiration-coefficients of both these gases have 

 been determined by Lord Eayleigh 5 ; he found the values 

 1-21 for argon and O96 for helium referred to air. Thence, 

 taking 0-000172 as the viscosity-coefficient for air, we obtain 

 for 



argon, 0-000208, 

 helium, 0-000165 



as the value of the coefficient of viscosity at 0, the tempera 

 ture for which that of air is given. 



Before we can calculate the free paths from these values 

 we must calculate also the molecular speed, for which the 

 values of the specific gravities are required. The density 

 of argon is given by Eayleigh as bearing to that of oxygen 

 the ratio 3*2746 : 2-6276, whence, by use of the numbers 



1 Pogg. Ann. 1875, civ. p. 540. 



2 Houdaille (Fortsch. d. Phy. 1896, 52. Jahrg. i. p. 442) finds the co- 

 efficient of viscosity of water vapour to be much smaller at low pressures, 

 probably as a consequence of dissociation ( 89). 



3 Wiener Sitzungsber. 1876, Ixxiii. Abth. 2, p. 589 ; Carl's Repert. f- 

 Experimentalphys. 1877, xiii. p. 293. 



4 Wied. Ann. 1884, xxiii. p. 353. 



5 Proc. Eoy. Soc. 1896, lix. p. 198 ; Zeitschr. f. phys. Chemie, 1896, xix. 

 p. 364. 



O 



