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The experimental work of this paper was begun by E. C. Humphery in 19x2, and was continued in 1913 by F. E. Brown. The delay in its publication has been caused by the fact that until recently WE had not determined accurately the corrections in-'H20 = 72.05, 'CsHs = 28.17, 'HzO.CsHs = 34.68,

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IntroductionThe first study of the peculiar structures obtained when two dissolved substances are allowed to react slowly to form a precipitate was made by Rungel in 1865, when he was attempting to add stiffness or rigidity to blotting papers. He conceived the idea of forming precipitates between the fibres of the paper by first saturating the paper with some soluble compound that would later be precipitated by the diffusion of a second soluble compound into the paper. In the course of his investigations he noticed peculiarities in the form and shape of the precipitates, which peculiarities he found to be a function of the rates of diffusion.Ord,* in 1869, accidentally obtained other growth forms when he allowed ammonium oxalate to diffuse into isinglass which was slightly impregnated with calcium chloride. The insoluble calcium oxalate was obtained in some very fantastic forms, quite different from those obtained when the two reacting salts were mixed in solution.While experimenting with diffusion phenomena, Lupton3 noticed that in certain cases layers or rings were produced. However, he merely mentioned their occasional occurrence and did not attempt to investigate them.It remained for Liesegangl in 1896, to report his exhaustive investigations of ring formation in gels. He is the first author to give exact data upon these ring structures, and is among the first to point out t'heir significance in explanation of geological diffusion phenomena. His first preparations were made by placing a drop of silver nitrate solution upon a glass plate that had been coated with gelat,in impregnated with potassium bichromate. This gave a series of concentric rings consisting of insoluble silver chromate, the rings being spaced a t wider intervals apart in proportion as the distance from the center increased.In 1914, E. Kiisters reported and described the rhythmic crystallizations obtained when trisodium orthophosphate, cupric sulfate, ferrous sulfate, potassium ferrocyanide, and ammonium sulfate separated from gelatin solutions on drying at ordinary temperatures. This is thought to be the

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