of Gaseous Ammonia, Thospliine, and Amine. 613 



The following table gives the results calculated on this 

 basis. 



Table VI. 

 All areas are in cm. 2 x 10" 15 . 



Gas. 



Ammonia 



Phusphine 



Arsine 



A. 



Gas. 



A=7T<7 2 . 



Difference. 



0640 

 0-911 

 0985 



Neon 



0-417 

 0-648 



0-757 



0-223 

 0-203 



0-228 



Arson 



Krypton 



It is of interest to compare the collision areas given in 

 column 2 of the above table with those of neon, argon, 

 and krypton respectively, for according to the Lewis- 

 Langmuir theory* somewhat simple relations may be 

 expected. Before doing so, however, we think it desirable 

 to make a tentative correction to the collision areas of neon, 

 krypton, and xenon already published f. These values 

 were obtained from viscosity measurements made by one of 

 us before the additional precision attainable by the method 

 described in this paper of allowing for the capillary effect 

 had been recognized. Consequently the values of Suther- 

 land's Constant found are in all probability too small, and 

 the deduced collision areas too large. It is of course 

 impossible without repeating the measurements to settle this 

 question definitely, but unfortunately these rare gases are 

 no longer available. But there remains a method of estim- 

 ation which, although not exact, most certainly improves the 

 accuracy of the results. In the case of argon the value 

 obtained for Sutherland's Constant was 142 as compared 

 with 162, given by Chapman as the best value, and used for 

 calculating the molecular dimensions, the viscosity of argon 

 having been measured by several other investigators. This 

 difference is considerable and corresponds to a change of 

 about 4'5 per cent, in the mean collision area. Assuming 

 that the values for C in the cases of neon, krypton, and 

 xenon are too low by corresponding amounts, we have 

 recalculated them and deduced corrected values for the 



* I. Laogmuir, Joum. Amer. Cliem. Soc. vol. xli. p. 868 (1919). 

 t A. O. Ranking Proc. Roy. Soc. A. vol. xcviii. p. 360 (1921). 



