The direct colorimetric determination of uranium, in the presence of moderate or large amounts of iron, is not possible by other methods. By the 8-quinolinol method, uranium may be determined in the presence of 500 mg. of iron, 50 mg. of copper, 20 mg. of nickel, or 20 mg. of cobalt without prior separations. In conjunction with the hydrolytic separation by which uranium is separated from most of the colored ions but not iron, uranium may be determined colorimetrically, as a routine technique. With an ordinary Beckman spectrophotometer 10 of uranium are easily determined.

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These decomposition rates will be of prime interest in operating the newer homogeneous reactors he fuel for homogeneous research reactors is enriched uranium present as uranyl sulfate in an ordinary (light)

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METHOD of determining the acid numbers of mineral oils by electrometric titration in amyl alcohol solu-A tions has been described by Seltz and McKinney f2). Quinhydrone electrodes were used with the reference aolution joined by an agar-agar bridge. The objection to this method is the inconvenience of preparing the reference electrodes which must be replaced frequently. A method which overcomes this difficulty is described in this article. It has been found that a silver-silver chloride electrode functions satisfactorily as a reference electrode and can be used for numerous titrations without deterioration. Furthermore, the method Jyas found to be applicable not only to mineral oils but also to vegetable and animal oils and fats. -0.2 I i -0 1 0 0 --i -0 1 -0 . 2 2 3 cc. for curves -4 , E , G, H 9 11 13 15 17 cc. for curves 0 2 B, C, D , F Figure 1Butyl alcohol seems to be somewhat more satisfactory than amyl alcohol as a solvent medium and waq used throughout the investigation here reported. Reference ElectrodeThe silver-silver chloride electrode m s of the type described by Koyes and Ellis (1). -4 platinum spiral was sealed into a glass tube and electrical connection was made with mercury. A thin layer of silver n-as electroplated on the platinum from a potassium silver cyanide solution and the spiral was then covered with a pasty ball of moist silver oxide and dried a t 100' C. in an oven. Three or four appli-1 Received J u n e 7 , 1929 cations of the oxide, with subsequent drying, were necessary to cover the spiral completely. The electrode was then heated for an hour a t 450" C. to coiivert the oxide to metal, and finally a thin layer of silver chloride was formed on the surface by electrolysis in dilute hydrochloric acid. This electrode replaced directly the quinhydrone reference electrode described in the previous publication ( 2 ) in which details of the apparatus are shown. The total cell reaction with this combination is probably represented by the equation Quinone Hydroquinone and the electromotive force (at 25' C.) of the cell is given by the equation CfiHaO, + 2 H C + 2C1-+ 2Xgo F* C~H~O ? H Z f 2AgC1 E = E " + -O.Oj91 (Quinone) X i H + ) * X (CI-)? 2 log (Hydroquinone:As (quinone) = (hydroquinone) and (Cl-) rerri:iin? practically constant, it is seen that the electromotive force of the cell during a titration is determined 11y the concentration of Hion in the solution. That this is correct is shown by the forms of the titration curves, which give evcellent inflwtions a t the end points. Figure 2 ProcedureThe procedure is similar to that described in the previous publication ( 2 ) . The solvent was prepared by saturating n-butyl alcohol (Eastman Kodak) with lithium chloride.