Lerts ano Brake—Estimation of Oxygen in Solution. 467 
divided into two portions. To one of these a standard solution of 
potassium nitrate was added in such quantity that the resulting 
mixture contained 0°7 grains per gallon of nitric nitrogen (or 1 
part in 100,000). ‘The dissolved oxygen was then determined in 
both portions, the titrations being made with strong permanganate 
(1 ec. = 1 cc. of oxygen at N.T.P.). 
Series 1.—Aerated Yap Water alone. 
(1) Oxygen determination required, . . 1:53 e.c. KMnO, 
(2) 96 Bh a : 5) POS) 55 Ph 
Aerated Tap Water with added Nitrate. 
(1) Oxygen determination required, . . 1°53 c.c. KMn0, 
(2) 23 ”? 9 s © 1-56 yr) 99 
(3) ) ) 2) : ie 1°53 ? 9) 
Mean, Pia lira: bales ‘ 
For the above determinations a very old solution of ferrous 
sulphate was used, and by an oversight a blank determination was 
made with the aerated tap water only and not with the nitrated 
water in addition as had been intended. ‘Taking this one deter- 
mination as the basis of calculation, the amount of dissolved oxygen 
was as follows :— 
Aerated Tap Water alone. 
Blank experiment required, : . 93°98 c.c. KMnO, 
Oxygen determination (mean) required, 1°58 
oP) 29 
Dissolved oxygen, . 2°45 c.c. 
Dissolved oxygen, per litre, , 5 (°8l CG. 
Aerated Tap Water with added Nitrate. 
Blank experiment required, . . 398 c.c. KMnO, 
Oxygen determination (mean) required, 1°54 ,, 
Dissolved oxygen, . 2°44 c.c. 
Dissolved oxygen, per litre, : - (84 Cc. 
