Methane and Sulpkuretted Hydrogen. 617 



At 17°'0 C. the viscosity of air is 1*808 X 10" l C.G.S. units, 

 whence for methane, ^ 17 =l'094x 10~ 4 C.G.S. units, 

 and 77 100 =r363x 10~ 4 C.G.S. units. 



Sulphuretted Hydrogen. 



The sulphuretted hydrogen was made by the action of 

 dilute hydrochloric acid on zinc sulphide. The gas was 

 washed with water to remove traces of hydrochloric acid, 

 and dried by passing it through a tube surrounded by a 

 mixture of solid carbon dioxide and alcohol at about —80° C. 

 The gas was then solidified in a tube surrounded by liquid 

 air. When the reaction was over, this U-tube was cut oft* 

 from the rest of the apparatus and connected to the visco- 

 meter and a Toepler pump by means of a three-way tap. 

 The viscometer was exhausted and then shut off from the 

 remainder of the apparatus. The permanent gases were 

 pumped off from the U-tube containing the solidified sul- 

 phuretted hydrogen. The liquid air was then removed from 

 the U-tube, and a portion of the gas drawn over into the 

 reservoir of the pump. Several portions of the gas were 

 drawn over and rejected, but finally one sample was intro- 

 duced into the viscometer at atmospheric pressure. In this 

 way a sample of pure dry sulphuretted hydrogen was obtained. 

 Sulphuretted hydrogen apparently acts slowly on mercury 

 even when dried to this extent, and changes of surface tension 

 phenomena were exhibited. The observations with this gas, 

 therefore, had to be carried out with all possible speed, and 

 the procedure adapted to allow for a changing capillary 

 correction. This, we believe, we have successfully accom- 

 plished by taking observations in the following order : 



(1) with the pellet intact, 



(2) „ „ „ in two segments, 



(3) „ „ „ again intact, 



at both atmospheric and steatn temperatures, and combining 

 the mean of (1) and (3) with (2) to calculate the capillary 

 effect. On the completion of the observations the motion of 

 the mercury pellet was not so smooth as at first ; but no 

 measurable quantity of permanent gas was found when the 

 sulphuretted hydrogen was condensed after the experiment. 

 Thus the chemical effect of the action between the mercury 

 and the gas was negligible. 



Phil. Mag. S. 6. Vol. 42. No. 251. Nov. 192J. 2 T 



