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LXXIL On the Viscosities and Molecular Dimensions of 

 Methane, Sulphuretted Hydrogen, and Cyanogen. By 

 A. 0. Rankine, Jf.Sc:, Professor of Physics, and C. J. 

 Smith, B.Sc, A.B.C.S., Research Student, Irhperial Col- 

 lege of Science and Technology, London*. 



ri^HE measurements of the viscosities of methane and sul- 

 JL phuretted hydrogen, here described, were undertaken 

 to provide the necessary data for estimating the molecular 

 dimensions of these two gases. Certain values of the vis- 

 cosities are already extant, but they do not extend over 

 ranges of temperature adequate for the calculation of Suther- 

 land's Constant, a factor of almost as much importance in 

 the calculation as the viscosity itself. The data we have 

 obtained correspond fairly closely with those already in 

 existence, and at the same time give the variation of viscosity 

 over the range of temperature from 17° 0. to 100° C. It 

 has thus been possible to find the mo'ecular dimensions of 

 these gases with a probable accuracy of something like 3 per 

 cent. The method used has been already fully described!,, 

 and we have taken advantage of the additional precision 

 which can now be obtained with it to repeat the viscosity 

 measurements for cyanogen. The values recently published^ 

 by one of us for this gas consequently require correction of 

 the amount indicated below\ 



Experiments and Results. 



The viscometer was standardized carefully with a new 

 mercury pellet in the way indicated in our previous paper, 

 and the corrected time of fall at 17° C, deduced from three 

 series of observations, proved to be 12398 sees., a value which 

 is probably correct to O'l sec. TVith this time the corre- 

 sponding times of fall for the three gases have been compared ; 

 and, after applying the appropr ate slipping corrections, the 

 viscosities have been deduced by assuming the known value 

 for air. In addition, for each gas, the ratio of the corrected 

 times of fall at 100°C. and 17° C. have been found, and the 

 values of Sutherland's Constant calculated therefrom. 



* Communicated by the Authors. 



t A. O. Rankine and C. J. Smith, supra, p. 001. 



\ A. O. Rankine, Proc. Roy. Soc. A. vol. xcix. p. 33] (1921 V 





