Gaseous Ammonia, PJiosphine, and Arsine. 605 



the application of the small correction for slipping appro- 

 priate to the particular gas to make it proportional to the 

 viscosity. The slipping corrections have been applied in the 

 same way as that already described *', and their values are in 

 no case greater than 0'2 per cent. 



Details of the preparation and purification of the gases 

 are given below. In each case the purity was proved by 

 the fact that the contents of the viscometer were found to be 

 wholly condensable at liquid air temperature, both before 

 introduction and after removal. 



Air. 



The air which was used as a standard of comparison was 

 deprived of its water vapour by allowing it to remain in 

 contact with phosphorus pentoxide for a considerable time 

 before introduction to the viscometer. The removal of water 

 vapour is important, not only from considerations of purity 

 of the gas under test, but also to ensure smooth running of 

 the mercury pellet in the tube ; in fact, the steady motion 

 of the mercury pellet in the fall tube can bo taken as a 

 criterion of the dryness of the gas as well as of the cleanliness 

 of the tube. The apparatus was cleaned with aqua regia, 

 rinsed with distilled water and absolute alcohol, and finally 

 dried by being exhausted and allowed to remain in connexion 

 with a bulb surrounded by liquid air. 



Results : — 



Table I. — Dry Air. 



Each recorded time is the mean of twelve observations, 

 mutually consistent to 02 per cent. 



Temperature 

 (cleg. C.). 



Time of fall 



in seconds. 



Capillary 

 Correction 



Corrected 

 Time 



(0. 



Whole pellet. 



Two segments. 



(a) 150 



132-02 



139-50 



0-0513 



125-25 



(b) 15-0 



13T75 



138-83 



00485 



125-35 



(c) 15-0 



130-61 



130-30 



0-0405 



125-33 



(d) 15-0 



129-78 



134-73 



0-0355 

 Mean 



125-18 

 125-28 



(e) 100-0 



159-03 



107-38 



143 



152-50 



In the above results small temperature corrections have 

 * A. O. Rankine, Proc. Rov. Soc. A. vol. lxxxiii. p. 517. 



