The letters of Faraday and Schoenbein, 1836-1862 : with notes, comments and references to contemporary letters / edited by Georg W.A. Kahlbaum and Francis V. Darbishire.

Date:: 1899

Credit: The letters of Faraday and Schoenbein, 1836-1862 : with notes, comments and references to contemporary letters / edited by Georg W.A. Kahlbaum and Francis V. Darbishire. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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$to detect the millionth part of the said peroxide contained in water and even less than that. I hese tests depend upon the oxidizing and reducing effects ])roduced by HO 2 u])on certain substances. Dilute ])aste of starch containing some jodide of potassium, if it be mixt u|) with water containing but half a millionth of HO2 is within a very short time colored darkblue on adding some drops of a weak dissolution of any proto.xide salt of iron to the mixture. The dilute dissolution of HO 2 slightly acidulated by SO3 discharges the red color of an acidulated dissolution of the permanganate of potash (b_v reducing the acid of that salt to the protoxide of manganese). HO2, even in a most dilute state, throws down prussian blue out of a mixture of most dilute dissolutions of the red cyanide of po- tassium, and any peroxide-salt of iron (by reducing Fe2 0:} to FeO). Most dilute HO2, colored blue by some Indigo- solution, is rapidly discolored, on adding some drops of a dilute solution of iron vitriol to the mixture. A dilute solution of chromic acid is certainly a less delicate test for HO2 than the mentioned ones are, but its property of being colored azureblue bv water, containing but —of HO2 makes it in ^ ' ^20 000 many cases a valuable and practical test, which I always use when I have to deal with water somewhat rich in HO2. Now by the means of those tests I have of late ascertained, that during the slow oxidation of Zinc, Cadmium, Lead, Tin, Bis- muthum and Copper (effected by moist common oxigen or atmospheric air), perceptable quantities of HO 2 are always formed conjointly with the oxides of those metals. To pro- duce HO2, some of the metals being in a state of mechanical division as Zinc, Cadmium and Lead, ha\e but to be put in contact with pure water and atmospheric air for a very short time, hut I find it more convenient to amalgamate first the metals with mercur}^ Take for instance 100 grammes of Zinc filings, and the same quantity of Mcrcur}', put them into a tumbler filled with dilute sulphuric acid, stir uj) the metals$