Excerpt from Standardization of Potassium Permanganate Solution by Sodium Oxalate
The water and sulphuric acid employed were frequently tested for reducing matter and in each case were shown to be free from appreciable amounts of such impurities. The manganous sulphate was si... milarly tested for reducing and oxidizing in¿uence and shown to be satisfactory. To purify the air used for the tests of Tables VI and VII, it was passed through cotton wool to remove dust and grease, bubbled through a solution of potassium hydroxide to take out any acid vapors present, and then through, solutions of chromic acid and potassium permanganate. The purified air had no detectable reducing efiect upon dilute solutions of permanganate under the conditions of titration.
The carbon dioxide used for the tests of Table VI was taken from a cylinder of the commercial liquid and passed through water, chromic acid, and permanganate solution before use. An analysis showed the presence of about 3 per cent of methane; but this gas seemed to have only a very slight reducing action on the permanganate in dilute solution, so that the results of the series in which it was used can be regarded as but slightly less reliable than the series in Table VII. For this latter group of tests, pure carbon dioxide was made from acid and soda. This source gave a gas which had no detectable reducing action under the conditions of its use.
The potassium permanganate used for most of the work was a sample of good quality which had been made up in normal solution for over six months before filtration and dilution to tenth normal strength for use. The diluted solution was filtered frequently through asbestos to insure freedom from precipitated manganese dioxide. For the series of tests reported in Table IV, b, a second permanganate was used. In this case the strong solution was boiled for a few minutes, cooled, filtered, and diluted to tenth normal strength. For the series of Table VII still a different permanganate was employed, this stock being prepared in the same manner as the main solution. About 40 grams of solution were used for each titration.
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