The fact that polymerized metaphosphates can inhibit as well as entirely prevent the precipitation of calcium carbonate has been applied on an industrial scale in the conditioning of boiler water, in flotation, in the removal of calcareous incrustations, in the stabilization of sols, and in other processes. These applications have, in the main, been developed by Hall (4). In those processes in which the water is completely softened, Hall4 states that the metaphosphate must be added in the proportion of ". . . 4 formula-weights of sodium metaphosphate to 1 formula-weight of calcium at a pH of 8.5, but 7 formula-weights of sodium metaphosphate were required for this amount of calcium when the pH value was 10." The calcium is assumed to be present in the form of a stable complex from which it cannot be precipitated either as the carbonate or as an insoluble soap. The exact composition of this complex has not yet been definitely established.A more recent application of sodium metaphosphate has been made by Rosenstein (11) for the prevention of calcium carbonate deposition from irrigation water when anhydrous ammonia is introduced as a source of nitrogen for growing crops. It was discovered that the precipitation of calcium carbonate can be prevented by an extraordinarily minute con-1 This paper is part of a dissertation submitted by R. F. Reitemeier to the Graduate College of the University of Arizona in partial fulfillment of the requirements for the degree of Doctor of Philosophy, which was conferred June 1, 1938. A more detailed account of this investigation, including the results of later work, is soon to appear in a Technical Bulletin of the Arizona Agricultural Experiment Station.! Presented before the Division of Physical and Inorganic Chemistry at the Ninety-sixth Meeting of the American Chemical Society, held in Milwaukee, Wisconsin, September, 1938.

The purpose of this investigation was to measure the potential of the gold-auric oxide electrode and to calculate the free energy of formation of auric oxide from its elements at 298°A.The cell chosen for these measurements was H2 (g), H2SO4 (x-M), Au203 (s), Au (s). A careful search of the literature showed that very little work had been done on the potential of the gold-auric oxide electrode. Jirsa and Jelinek2 in their work on the anodic oxidation of gold arrived at a value of 1.36 volts, referred to hydrogen. The aim of the present research was to extend the accuracy of this value, if possible, by the use of cell substances of such purity and homogeneity that true equilibrium would

CALCIUM CARBONATE FROM AMMONIACAL SOLUIn a previous paper by the authors (14) it was shown that the inhibiting effect of metaphosphates on the precipitation of calcium carbonate manifests itself as either a retardation of precipitation or its complete prevention, depending upon the properties of the reacting components present in the solution, primarily those of calcium bicarbonate and sodium hexametaphosphate. Chemical studies designed to explain the mechanism of this process have shown definitely that it is not due to some mysterious interaction between metaphosphate and bicarbonate ion, or carbonate ion, or the ammonia. Nor does it affect the possible interactions between these constituents. The minuteness of the concentration of metaphosphate which is effective in this process would appear to eliminate complex formation between calcium ion and the hexametaphosphate as a possible explanation, since only an extremely small amount of it is necessary to prevent precipitation completely. The quantitative evidence obtained in these studies has proved, moreover, that the primary precipitation reaction, represented by the simple equation Ca* + HCOB + OH-= CaCOds) + &O is not affected by traces of hexametaphosphate.The only other plausible basis for explaining the mechanism must be sought either in the effect of hexametaphosphate on the nature of the solid phase which separates out, or in the conditions attending the crystallization process. Preliminary experiments had shown that, when calcium carbonate was precipitated from calcium bicarbonate by the addition of ammonia, the crystals formed rapidly, did not adhere to the walls of the vessel, and settled readily. If, however, the same precipitation was carried out in the presence of one part per million or less of hexameta-1 Presented before the Division of Physical and Inorganic Chemistry at the Ninety-sixth Meeting of the American Chemical Society, held at Milwaukee, Wisconsin, September, 1938. See footnote to Paper I of this series for additional information.

Jelinek,2 and appears to be evidence of the fact that the reaction 3Au20 = Au2Os + 4Au takes place. The constancy of the potential over a considerable period of time is considered significant, as well as the fact that the color of the blue-black precipitate had during this time changed to that of metallic gold. Dr. Gerke believes that the change in potential with the time can be accounted for by assuming that the electrode reaction is Au (colloidal) = Au (cryst.).It is certain that the black precipitate does undergo a change with the time, suggesting considerable instability. Further work on this problem is planned to study other possible methods of preparation in an endeavor to establish conclusively whether or not aurous oxide is capable of existence, and to measure accurately the value of its electrode potential.

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