AvENEY—On Absorption of Oxygen by Polluted Waters, &e. 283 
The pressure in B will be that of the atmosphere, and in 4 
that of the atmosphere plus that due to the column of water in 
the capillary tube a, less the height to which the water rises in it 
by capillary action. If the polluted water be a strong one, the 
apparatus is put into a mechanical shaker; and the contents of 
the two bottles are kept in gentle motion. If, however, it be a 
weak one, this will be unnecessary; an occasional shake of the 
two bottles will be sufficient. The apparatus should be kept at a 
temperature of 15° to 18°C. 
The principle on which the apparatus works depends upon 
the fact that the atmosphere in the bottle A remains practically 
unchanged in composition during the time of the experiment ; 
and the bottle A consequently acts as a standard pressure bottle. 
As the oxygen is absorbed in the bottle B, the pressure of its 
atmosphere will be reduced in direct proportion to the loss of 
oxygen, as no carbon dioxide will be evolved from the polluted 
liquid owing to its fixation by the magnesium hydrate pre- 
viously added.’ If, therefore, the stopcock J; be opened, the 
water will rise above the zero of the scale of the tube aa in 
proportion to the loss of pressure in B. ‘The volume of water 
which so rises into the graduated portion of the tube aa, at any 
given time, and the height of it above the zero-mark, give the 
meaus of calculating the volume of oxygen absorbed by the 
polluted water in B during the period of observation ; thus— 
Let ov’ = volume of oxygen absorbed from atmosphere in B, 
at initial temperature and pressure. 
V = volume of air in A or B at’ commencement. 
v =volume of water that rises above the zero of the 
scale of the tube aa. 
p’ =height of water in the capillary tube a above the 
level it assumes by capillary action. 
p’ = height of water in the graduated tube above the 
zero-mark on the scale. 
p=p +p. 
P =pressure of air in Bat commencement, in terms of 
the water-barometer. The pressure in A at 
commencement will be P + p’. 
1 If crude sewage be the subject of examination, it should be diluted to five or ten 
times its volume with tap-water before being put into B; such dilution prevents 
