218 Mr. Waldie’s investigations connected [No. 3, 
of which act slowly on it, others more rapidly. Dr. Miller strictly 
enjoins that the water should not be warmed, without however stat- 
ing any reason, and other English chemists seem also to practise it 
cold; Dr. Woods, who wrote a paper on it some years ago published in 
the Chemical Society’s Journal, recommends warming the water, as 
also does Dr, Macnamara, and gives reasons for it. It-now generally 
seems to be agreed that it is desirable to restrict the use of the 
permanganate to the oxidation of those substances that can be rapidly 
acted on; and after consideration and experiment, I have adopted with 
some small modifications the details of Dr. Frankland’s practice, except 
that the water is heated to about 120° F. at the commencement. 
English chemists forget that what is our natural cold here, requires 
artificial heat with them, and that it is desirable to follow a plan that 
can be easily made uniform for all climates. The solution of per- 
manganate is added in small portions at intervals, until a perceptible 
tinge of pink remains for ten minutes; when this is the case, the 
quantity used is read off. I use 4000 fluid grs. of water with 80 fluid 
ers. of diluted sulphuric acid, containing 1 grain concentrated acid by 
weight in 5 fl. grs., heat the whole to about 120° F. and having 
removed it from the lamp, proceed to add the solution. This is made 
of such strength that each measure of the tube (it may be, each equal 
to 1 cubic centimetre or to 10 fluid grains) yields .001 grain oxygen 
as ascertained by its action on oxalic acid in solution in similar 
circumstances, that is dissolved in a similar quantity of pure distilled 
water with the same quantity of sulphuric acid and treated in the 
same way. As .63 grains oxalic acid requires .08 grain oxygen, the 
solution will be of proper strength, if 80 measures are required for 
oxidizing that quantity of oxalic acid: that is, 80 measures are equal 
to .08 grain oxygen, or 1 measure is equal to .001 grain oxygen. 
Although it is certain that in many or most cases the permanganate 
as used in this process does not oxidise all the organic matters, and 
that we cannot tell how much remains unacted upon; and though 
at present at least we do not know what is the particular chemical 
constitution of the matters oxidized, it is at least certain that it acts 
upon those substances which give the putrid odour to stagnant water, 
and renders them after a time, when the products of its action have 
settled, pure and transparent and quite free from offensive smell+ 
