550 Scientific Proceedings, Royal Dublin Society. 
expeditiously and completely effected by the former method, 
and as the water may be kept in ebullition at a temperature a 
few degrees above that of the water in the condenser, there is 
much less risk of the decomposition of any of the solid matter in 
solution than when a method requiring a greater elevation of 
temperature is resorted to. If one desires to examine the gases 
at different stages of the operation this method affords every 
facility for that purpose. 
It might be supposed that in the operation I have described a 
quantity of water would necessarily be carried over to the pump, 
and eventually conveyed to the vessel in which the gases are 
collected. It must be remembered, however, that the temperature 
of the water circulating in the condenser is below that of the 
atmosphere, and since, according to the well-known law of the 
tension of vapours in communicating vessels of different 
temperatures, the tension of the aqueous vapour in the apparatus 
will correspond to the temperature of the condenser, it 1s obvious 
that instead of water being carried over to the pump the gases 
collected will not even be saturated with aqueous vapour, but 
will contain only a quantity of the vapour of water corresponding 
to its comparatively low tension at the temperature of the 
condenser. 
