THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 

 CBXTB !! ta NWl4 19a ) 



S OV EMBER 



LXXI. On the Viscosity and Molecular Dimensions of Gaseous 

 Ammonia, Phosphine, and Arsine. By A. 0. Rankine, 

 D 8c, Professor of Physics, and 0, J. Smith, B.Sc, 

 A.R.C.S., Research Student, Imperial College of Science 

 and Technology *. 



ri^HE present research was undertaken to determine the 

 JL viscosity at different temperatures of the gases ammonia, 

 phosphine, and arsine, with a view to estimating- their 

 molecular dimensions. It seemed probable that a knowledge 

 of these dimensions for molecules so similar in chemical 

 constitution would throw light on the way in which the 

 constituent atoms are linked in the molecules. It was hoped 

 to include stibine in the group, but no results have been 

 obtained, on account of the almost instantaneous decomposition 

 of this gas even at ordinary temperatures. Our observations 

 have provided, however, new and sufficient data for the 

 other three gases, and we have been able to calculate, by 

 means of Chapman's formula f, the sizes of the molecules 

 NH 3 , PH 3 , and AsH 3 . 



Apparatus and Method of Observation. 



The apparatus, described elsewhere t, consists of a complete 

 circuit formed by two glass tubes, one a capillary, and the 



* Communicated by the Authors. 



f S. Chapman, Phil. Trans. A. vol. cc.vvi. p. CAT. 



X A. 0. Rankine, Proc. Roy. Soc. A. vol. Ixxxiv. p. 182. 



Phil Mag. S. 6. Vol. 42. No. 251. Nov, 1921. 2 S 



