Hydrocarbon-compounds contained in the Atmosphere. 543 



them never came in contact with organic matter. This was 

 effected by covering the corks a with a layer of mercury of suffi- 

 cient thickness. 



The mercury was introduced through the drawn-out point of 

 the tube b, by means of another tube drawn out to a still longer 

 and finer point, and serving as a funnel. 



Before filling the apparatus with lime-water the air contained 

 in it was replaced by air free from carbonic acid, and in like 

 manner the tubes b, which serve to connect the different vessels 

 containing lime-water, were filled with air deprived of carbonic 

 acid immediately after being placed on the corks and before the 

 mercury was poured in. After the introduction of the mercury, 

 air free from carbonic acid was again passed into them, in order 

 to displace any common air which might have got in during the 

 pouring in of the mercury, and they were then immediately 

 closed by quickly melting off the drawn-out points. 



In order to exclude any possibility of the leakage inwards of 

 common air at any accidental orifice, the air experimented upon 

 was not drawn, but pressed, through the apparatus*. 



* The whole apparatus was, moreover, found to be perfectly air-tight 

 before beginning the experiment, and no leakage arose during the course 

 of it. 



