116 On the Viscosity of Hydrogen as affected by Moisture. 



residual pressure gave 0-01114, 0*01122, 0*01118, 0-01126, 0-01120, 

 mean 0-01120. 



In the next experiments a phosphoric tube was added about 

 60 cm. long and closely packed with fresh material. The viscosity 

 appeared to be slightly increased, but hardly more than would be 

 accounted for by an accidental rise of temperature. The mean 

 uncorrected number may be taken as 0'0603. 



The evidence from these experiments tends to show that residual 

 moisture is without appreciable influence upon the viscosity of 

 hydrogen ; so much so that, were there no other evidence, this con- 

 clusion would appear to me to be sufficiently established. It remains 

 barely possible that the best desiccation to which I could attain was 

 still inadequate, and that absolutely dry hydrogen would exhibit a 

 less viscosity. It must be admitted that an apparatus containing 

 cemented joints and greased stop-cocks is in some respects at a 

 disadvantage. Moreover, it should be noticed that the ratio 

 0'0600 : 0*1120, viz. 0*536, for the viscosities of hydrogen and air is 

 decidedly higher than that (0*500) deduced by Sir Gr. Stokes from 

 Crookes's observations. According to the theory of the former, a 

 fair comparison may be made by taking, as above, the logarithmic 

 decrements for hydrogen at atmospheric pressure, and for air at a 

 pressure of 10 cm. of mercury. I may mention that moderate rare- 

 factions, down say to a residual pressure of 5 cm., had no influence 

 on the logarithmic decrement observed with hydrogen. 



I am not able to explain the discrepancy in the ratios thus 

 exhibited. A viscous quality in the suspension, leading to a sub- 

 sidence of vibrations independent of the gaseous atmosphere, would 

 tend to diminish the apparent differences between various kinds of 

 gas, but I can hardly regard this cause as operative in my experi- 

 ments. For actual comparisons of widely differing viscosities I 

 should prefer an apparatus designed on Maxwell's principle, in 

 which the gas subjected to shearing should form a comparatively 

 thin layer bounded on one side by a moving plane and on the other 

 by a fixed plane. 



