High-temperature phase equilibria in the system 2CaO,Si0,-3Ca0,P20, have been investigated by high-temperature microscopy and X-ray analysis. The system presents a continuous series of solid solutions with a meltingpoint maximum at 2240", contradicting earlier findings. A new high-temperature form of 3Ca0,P20, has been discovered which does not survive quenching to room temperature, but is completely miscible with the a form of ZCaO,SiO,.A t lower temperatures two compounds are formed by solidstate reactions, the known silicocarnotite stable below 1450" and a new phase, denoted as " A," stable below 1125", having the approximate composition 7Ca0,P20,,2Si0,. Powder X-ray measurements are given for each phase in the system, either as obtained in a specially designed high-temperature X-ray camera or, where appropriate, as recorded at room temperature in a focusing camera.THE section 2Ca0,Si0,-3Ca0,P,05 in the ternary system Ca0-Si02-P205, which is relevant to processes in the steel, cement, and fertiliser industries, has been examined la with widely differing conclusions. This divergency can be attributed to the experimental Tromel, Stahl und Eisen, 1943, 63, 21.

A revised phase diagram of the partial system ZCaO,P,O,-CaO is presented, incorporating a new phase field for ;-3CaO,P,O, and a region of solid solution between 3Ca0,P,05 and ZCaO,P,O,. PORTIONS of the system CaO-P,O, have been studied by several previous workers with differing conclusions.192 Interest in the larger system CaO-P,O,-SiO, prompted us to reinvestigate the partial system 2Ca0,P,05-Ca0 concerning which there is controversy in the literature. Furthermore, we have recently discovered a new form of tricalcium phosphate,3y4 and revision of previous phase diagrams is thus needed.Experimental.-The preparation of materials and experimental procedure were as described earlier,* except for the following. Volatilization of phosphorus pentoxide from substances varying in compositions between 2CaO,P,O, and 3Ca0,P,05, and of calcium oxide from those between 3CaO,P,O, and 4CaO,P,O, precluded the use of high-temperature X-ray analysis which requires prolonged heating of the specimen. Much of the system was explored by hightemperature microscopy, which is sufficiently rapid to avoid this difficulty, but for phase identification in the subsolidus region the traditional quenching method followed by X-ray analysis in a Guinier-type focusing camera was also used. was used to investigatc the possibility of solid solution between 4CaO,P,O, and CaO.Selective " free lime " analysis

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A portion of the system CaO-SiOz has been reinvestigated by high-temperature microscopy. Direct observations at the liquidus establish a primary-phase region for tricalcium silicate, which is shown in a revised phase diagram to melt incongruently. The tricalcium silicate primary-phase field extends from the eutectic with dicalcium silicate at 2O5O0C., 69.5y0 CaO, to the incongruent boundary with lime at 2070"c., 71.50/, CaO, with a possible error in composition of f 0.25%. The estimated accuracy of these temperatures is f 3" relative to one another, and f 10" relative to the melting points of alumina and dicalcium silicate, for which the values 204OOC. and 2130°C. taken from the literature have been assumed.

may be increased by the suction induced by the rapidly flowing water at the tip.Mayne 1 has shown that rapid oxidation of ferrous hy~roxide at a_pH_value greater than 5 gives goethite while slow oxidation leads to the formation of an intermediate between magnetite and ferric oxide (yFe 20 3 ). Thus the formation of goethite in the present case is readily explained. The formation of magnetite, the second constituent, is not likely to occur in the same area at the same time as goethite since slow oxidation would appear to be necessary. Therefore, the oxidation to form this compound must occur in some areas sheltered from the direct action of the water. This may occur in pockets of ferrous ion-containing water trapped in the goethite crystals or by slow oxidation of the ferrous ion during its passage through the whisker either by a small amount of oxygen contained in the water or by oxygen diffusing through the wall of the .tubule.