The preparation of the anhydrous chlorides of the rare earth elements is of considerable interest, since these compounds serve as the starting materials in the preparation of the metals, either directly by electrolysis in the fused state or indirectly by electrolysis in alcoholic solutions with a mercury cathode followed by the subsequent thermal decomposition of the resulting amalgams. The most important methods for the preparation of anhydrous rare earth chlorides previously suggested are : from the metals, by action of dry chlorine, hydrogen chloride, or methyl chloride1 at elevated temperatures; frdm the oxides, by action of chlorine in the presence of a reducing agent,2 by action of hydrogen chloride alone3 or with ~a r b o n ,~ by action of carbon tetra~hloride,~ carbonyl chloride,6 sulfur monochloride vapor7 (or a mixture of sulfur monochloride and chlorine) ,8 by heating with phosphorus penta~hloride,~ by mixing with a slight excess of ammonium chloride and gradually dropping the mixture into a red-hot c r~c i b l e ;~ from the sulfides, by heating in dry hydrogen chloride;1° from the carbides, by heating with chlorine1' or in a current of hydrogen chloride ; I z from the hydrated chlorides, by heating in a current of hydrogen chloride gas,13 by adding ammonium chloride to a solution of the chlorides, evaporating to dryness, and heating in air14 or in a current of HC1, l5 by dehydration in an atmosphere of carbonyl chloride (or a mixture of carbon monoxide and chlorine16), by heating in air and treating the resulting mixture of chlorides and oxychlorides with sulfur monochloride and chlorine or sulfur monochloride, chlorine, and hydrogen chloride mixtures, by extracting the chloride-oxychloride

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Vanadium pentoxide hydrosols, prepared by the hydrolysis of f-amyl orthovanadate, have been studied by optical absorption, light scattering and electron microscopy. These sols consist of long needle-like particles. Absorption is due to both scattering and true absorption within the particles. Electron microscopy shows that as the sol ages, the micelles are redistributed from numerous small rods to a smaller number of large filaments. This change is accompanied by up to thirtyfold increase in the optical density and more than one hundred-fold increase in light scattering. The magnitude of the increase in absorption is larger than anticipated by available theory. Gans' theory, applicable to small ellipsoids, predicts a very small increase in absorption. Mie's theory, applicable to spheres, does predict an appreciable increase in absorption but not of the magnitude observed for this system. A satisfactory theory of scattering by ellipsoids must account for these increases quantitatively and should differentiate the effect of size from shape. The vertical component of the scattered light is more intense than the horizontal. The scattering is more intense in the forward than in the backward direction. The vanadium pentoxide hydrosols are dissolved by dilution of the sol, and this is followed by slow fading of the optical density and scattering. Electron microscopic observations show that partial solution of the colloidal particles and not homogeneous ionic processes, as previously reported, causes this fading. A new value of the solubility of vanadium pentoxide, differing by more than 35% from the most recent value in the literature is reported (i.e., our value, 0.0296 g./100 cc. at 25°). The molar extinction coefficient of homogeneously dissolved vanadium pentoxide is reported from X 268 my to X 470 my.(1) Supported in Part by N.A.C.A. Contract NAw-8206.(2) (a) G.