The variation of potential of the cerium(IV)-cerium(lll) couple with the type of anion present is reviewed. The spectrophotometric data on sulfate complex formation and on hydrolysis correlate nicely with the potentiometric data, yielding a value of -

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Standard solutions of disodium dihydrogen ethylenediamine tetraacetate are being extensively used in determinations of hardness in water.The stability of these solutions is shown to be satisfactory at pH 5 in 1-gallon soft-glass bottles.Calcium chloride solutions are shown to be stable also. THE determination of total hardness in water using disodium dihydrogen ethylenediamine tetraacetate (disodium dihydrogen Versenate) was devised by Schwarzenbach and reviewed and further developed by Diehl, Goetz, and Hach (/),

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The iodometric determination of copper gives good results if the copper, arsenic, antimony, and iron are in their higher valence states, the iron is complexed with fluoride, the pH is maintained near 4.8, and thiocyanate is added just before the end point. Considerable time is required to dissolve sulfide ores with the common acids. In hot, concentrated perchloric acid such ores are dissolved in less than 5 minutes and all the metals are taken to their higher valence states.Results on pure copper and on sulfide ore demonstrate that the method is extremely precise and accurate as well as rapid.