218 Mr. Waldie's investigations connected [No. 3, 



of which act slowly on it, others more rapidly. Dr. Miller strictly 

 enjoins that the water shonld 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 

 grs. 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* 



