DIFFUSION OF GASES. 



325 



made to remove the disc ; when this is accomplished, the disc is 

 placed upon three small corks and left a whole day, so as to dry 

 thoroughly. The rim of the funnel is now heated, by holding it over 

 the lamp and constantly turning it, until hot enough to melt sealing- 

 wax, and a layer of sealing-wax is placed round the inside of the 

 rim. The funnel is then allowed to cool until the wax has partially 

 hardened, and it may be held nearly straight without the wax run- 

 ning down on the inside ; the thin lining of sealing-wax originally 

 put round the rim is now made thicker with a piece of sealing-wax 

 heated over the lamp ; the whole edge is again uniformly heated, 

 and the funnel is inverted over the disc of plaster. After cooling, 

 the wax which has been squeezed out is scraped off with the knife. 

 If the funnel is not quite round, it should be placed in the same 

 manner upon the disc as it was in the first instance when the disc 

 was cut out; otherwise the latter will not fit properly into the mouth 

 of the funnel. 



For the experiment with carbonic acid, the funnel should dip only 

 a few millimeters into the water, so as not to obstruct unnecessarily 

 the escaping gas-bubbles. For the experiment with coal gas or 

 hydrogen the tube must dip somewhat deeper, or the end of it would 

 above the surface of the water when the latter rises in the funnel. 



