ON THE DETERMINATION OF ORGANIC MATTER IN WATER. 
295 
nate in 10,000 grains of water should suffice. Its power may be exactly measured 
by means of a freshly prepared solution of crystallized oxalic acid, containing 
7*875 grains in 10,000 measured grains of water. 100 measures of this solution, 
warmed with a very dilute solution of sulphuric acid, should decolorize exactly 
100 measures of the permanganate. 0-05 gall. (8 oz.) of each of the several 
waters for trial are then placed in a flask with 30 grains of undiluted hydro- 
chloric acid, or 50 grains of diluted sulphuric acid (1 of acid to 3 of water). 
The permanganate may then be added, either in successive small doses till an 
excess is reached, or an excess may be added at once, and the excess determined 
at the end of the experiment. Either plan will answer. If the method by 
gradual addition be preferred, to each flask must be added 20 grains of the per¬ 
manganate solution, the flasks being arranged on a white ground side by side in 
front of a window ; no artificial heat must be employed. At intervals of fifteen 
minutes the flasks are examined, and successive quantities of 10 or 5 grains of 
the permanganate solution added in proportion as the colour disappears. 
These successive additions of the permanganate must be made until the last 
remains sensibly unaltered after the lapse of half an hour, which generally 
occurs between two and three hours from the commencement of the experiment. 
The number of water-grains of permanganate consumed in each case is then 
ascertained, deducting the last portion, which, it is estimated, remains unaltered 
in the flask. On multiplying by 20 the number of water-grains of permanga¬ 
nate solution consumed in each flask, we have the quantity of oxygen in ten- 
thousandths of a grain consumed in oxidizing the organic matter in one gallon 
of each sample of water. 
This process may be simplified by adding at once an excess of the solution of 
permanganate, allowing the whole to stand for three hours, and destroying the 
permanganate in excess by the addition of a reducing agent. This is best ac¬ 
complished, however, by the use of a little device. At the termination of the 
oxidizing action a small quantity of iodide of potassium and a little starch paste 
are added; the excess of permangauate is at once reduced to the state of a man¬ 
ganous salt, and the amount of iodine liberated may be determined by the addi¬ 
tion of a standard solution of hyposulphite of soda, which may be graduated 
by means of the permanganate itself. For this purpose 10 grains of the crystal¬ 
lized hyposulphite dissolved in 10,000 grains of water will furnish a solution of 
convenient strength. 
As might be almost anticipated, experiment has shown that the permanganate 
gives very different indications according to the kind of organic matter present; 
in only one instance, in fact, according to Dr. Frankland, in that of oxalic acid, 
did the permanganate solution show an amount equal to the quantity which had 
been purposely introduced ; whilst, on the other hand, nitrites, which are so 
frequently present, absorb a far larger quantity of oxygen than any form of 
organic matter, and thus lead to a very high and exaggerated estimate. 
“Whilst, however, this reagent,” says Dr. Frankland, “is quite worthless for 
the quantitative estimation of organic matter in water, it may still be used in 
certain cases as a qualitative test, where there is no opportunity for accurate 
analytical examination. Thus, if a clear and colourless water decolorizes much 
of the permanganate solution, the water ought to be rejected for domestic use 
as being of doubtful quality ; for although such a water may be absolutely free 
from organic impurity, yet its decolorizing action upon the permanganate 
would indicate, with considerable certainty, that the water had been in contact 
with decaying animal matters. Should the water, however, instead of being 
colourless, be tinged of a yellow or brownish-yellow colour, when looked at 
through a considerable stratum, as in a quart decanter, for instance, its capa¬ 
bility of decolorizing a considerable amount of permanganate solution ought 
not to be regarded with the same suspicion as in the case of a colourless water, 
