468 Scientific Proceedings, Royal Dublin Society. 
Series 2.1—The determinations were made in the same way 
as before, but a stronger solution of nitrate was added to the 
aerated tap water, so that the resulting mixture contained 10 
grains per gallon of nitric nitrogen. Blank experiments were 
made both with the nitrated and non-nitrated water, and a freshly 
prepared solution of ferrous sulphate was employed. 
Aerated Tap Water alone. 
Blank experiment required, : . 4°89 c.c. KMn0, 
Oxygen determination required, . a 238 is 
Dissolved oxygen, . 2°51 c.c. 
Dissolved oxygen, per litre, : 5 (GS OC; 
Aerated Tap Water with added Nitrate. 
Blank experiment required, j . 4°88 c.c. KMn0O, 
(1) Oxygen determination required, . | 239 2 
(2) 99 9? 99 " 2°39 99 99 
Dissolved oxygen, . 2°49 c.c. 
Dissolved oxygen, per litre, 3 2) 1 491C.0: 
From both series of experiments it is evident that the presence 
of nitrates in a water even in considerable quantities scarcely, if at 
all, affects the dissolved oxygen determination by the new process. 
Effect of Nitrites.—As nitrites are not only reducing agents, 
but also, when mixed with an acid, absorb atmospheric oxygen, we 
anticipated that their presence in a water might interfere with the 
new process in two ways. First, by reducing a larger volume of 
the permanganate or bichromate solution than might be suitable 
for the titrations; and second, by the absorption of atmospheric 
oxygen which would occur during the titration, the amount of 
which would, no doubt, vary with the time required for the latter, 
so that if the titration were performed rapidly, more of the 
bichromate or permanganate would be required than if it were 
performed slowly. 
1 Bach of the series of experiments, both with nitrates and nitrites, was made on 
different days, when no doubt the temperature at which the water was saturated with 
air was not quite the same: hence the variations in the amount of dissolyed oxygen 
found in the water. 
