282 Scientific Proceedings, Royal Dublin Society. 
The bottles A and B are two flat and shallow bottles of 
similar capacity. Each bottle is fitted with an ordinary cork 
previously soaked in melted paraffin. Through the cork of 4 
passes a capillary glass tube to the bottom of the bottle. ‘This 
tube is continued above the cork by a graduated one of wider bore, 
the upper end of which is enlarged to a small bulb, a, and then 
bent downwards as shown in the diagram, and continued down- 
wards until it passes through the cork of the second bottle B at 0 ; 
it is furnished with a glass stopcock 6,, just above the cork of B. 
By means of this connecting tube aa and stopcock, communication 
between the two bottles can be opened or closed at will. The cork 
of the bottle A is also fitted with a short tube and stopcock a,. The 
cork to the bottle B is likewise furnished with a second tube and 
stopcock 6,. Itis a capillary tube, and passes to the bottom of 
the bottle. 
To work the apparatus, the bottle B is partially filled with 
a known volume of the polluted water, previously mixed with 
a little magnesium hydrate to fix free carbon dioxide, and a 
similar volume of distilled water is poured into the bottle A. 
As the two bottles are similar in capacity, the volumes of the 
air-spaces left in them are also similar. The polluted water 
and distilled water should have been left in the laboratory 
for some little time previously to allow of their assuming a 
common temperature. The plug of the stopcock 0, is taken out; 
and the stopcock a is closed, and 6, is opened. The two corks 
are then inserted in their respective bottles, and the whole 
apparatus is put aside (or preferably immersed in a water-bath 
kept at the temperature of the iaboratory) for a few minutes 
to ensure their contents assuming the same temperature as that 
of the laboratory. This is noted, and also the height of the 
barometer. The effect of keeping the stopcock a, closed during 
the operation of inserting the corks into their respective bottles, 
as above described, will be found to cause a rise of the water 
through the capillary tube a, and above the zero point of the 
graduated portion immediately above it. This stopcock is 
now cautiously opened to allow the water in the graduated 
portion of the tube to sink down to the zero-point; it is then 
closed. The stopcock 6, is also closed, and the plug of 0, is 
replaced. 
