March, 1923 SOI,UBl~ITY IN MIXTURES WITH POLAR COMPONENTS 633 2. The oxidation takes place according to the theoretical requirement of 2 equivalents of oxygen, and the oxalate factor for the permanganate may be used. The maximum in the --V curve described usually lies a little too far to the right, but when a correction of -0.10 cc. of 0.1 N titrating solution is made the maximum error is less than 0.4 mg. of bromine.3. A sub-maximum often precedes the end-point maximum in the V curve and the intervening sub-minimum lies extremely close to the theoretical end-point. The sub-maximum does not always occur. 4. Iodide, if present, is oxidized to the corresponding iodine compound, ICN, but chloride in any quantity does not interfere. Since a selective determination of iodide is possible, the proposed method provides an excellent means for the rapid determination of bromide in the presence of any concentration of the other two halides.Iodide may be accurately titrated electrometrically by oxidation to iodine cyanide with permanganate in hydrocyanic acid solution in all concentrations of chloride and in moderate concentrations of bromide.The effect of bromide is a function of the ratio of its concentration to that of iodide and also of the absolute concentration of each. 6. A more accurate method is the oxidation of iodide to iodate by excess of alkaline hypobromite, the excess being titrated electrometrically with arsenite.The presence of any amount of bromide or chloride is without effect. Either the bimetallic or monometallic electrode system may be used AE AV nv-
.in both methods.
The results of molecular orbital calculations are presented in an attempt to answer four questions concerning the electronic structure of N4S4 and its derived ions. The important conclusions are: (1) A geometrical structure involving coplanar nitrogen atoms is to be preferred over one involving coplanar sulfur atoms. (2) Appreciable bonding is to be expected between sulfur atoms located on the same side of the plane defined by the four nitrogen atoms. No bonding is to be expected between nitrogen atoms. (3) Negative ions of N4S4 having one to four units of charge ought to exist and exhibit x-electron-delocalized electronic structures.
A limited inquiry has shown that the order of presentation of the principles involved in Boyle's and Charles' laws to students of chemistry and physics is very often from generalization to fact rather than from fact to generalization. This is especially true of the law of Charles dealing with the effect of temperature upon the pressure (or the volume) of an enclosed gas. It was thought that if a rapid method for the determination of the necessary data were described, more use might be made of the experimental approach to this important subject.The effect of pressure, at constant temperature, upon the volume of an enclosed gas is easily demonstrated by a variety of simple experiments.
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