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The table shows some typical results obtained by this method with samples containing known amounts of iodine. The iodine was added in the form of potassium iodide to samples of mineral mixture containing no iodine or a very slight trace. Blanks were always run on the samples used and on the reagents.Samples which contain no charcoal or bone meal may be fused with 20 g. of sodium hydroxide alone, omitting the potassium nitrate except for the addition of a few small crystals at the end of the fusion. Summary A method is described for the quantitative determination of small amounts of iodine in mixtures of mineral salts, charcoal, spent bone black, etc. The method is a modification of Kendall's and involves fusion with sodium hydroxide and potassium nitrate, removal of interfering substances, oxidation with bromine and determination of the iodine iodimetrically. Necessary conditions are outlined. Other methods were found very unsatisfactory for complex mixtures except when the samples were freshly prepared. Quincy, Illinois

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or as a weak electrolyte. It seems probable, however, that even the pure hydride if it could be obtained in the molten state would prove t o be an excellent conductor of electricity. Summary X new method was worked out for the preparation of pure sodium and potassium hydrides. They were obtained in the form of beautiful white, needle-like crystals. Potassium hydride decomposes with explosive violence in moist air. Calcium hydride was prepared free from metallic calcium. The eutectic mixture of potassium and lithium chlorides was found to be a solvent for hydrides. X solution of calcium hydride in this eutectic mixture was electrolyzed, and hydrogen was given off a t the anode in the quantity required by Faraday's law. 'l'he writer wishes to acknowledge his appreciation of the many helpful suggestions of members of the Faculty a t the University of California where this investigation was made, and to thank Professor G. N. Lewis especially, a t whose suggestion and under whose direction this research was prosecuted. No gas was liberated a t the cathode.

POLARIZED ELECTRODES IN ANALYSIS 19 4. A freshly ignited platinum electrode, immersed in a solution of silver nitrate, usually acquires the electromotive behavior of silver. This is probably due to an invisible coating of that metal.