not Available.

A study has been made of the mechanism of the reaction taking place when zinc is unodically treated in potassium hydroxide solutions. The zinc-containing ion present in solution as a result of the anodic treatment is Zn(0H)T. However, zinc oxide or hydroxide is an intermediate leading to the formation of Zn(OH)T. This latter ion then decomposes slowly to form zinc oxide.

Light scattering, density, and viscosity data are presented for electrolytically prepared supersaturated zincate solutions that were allowed to decay naturally. The results indicate that the solute species in the supersaturated solutions are not completely different from those in saturated or unsaturated zincate solutions. An explanation for the formation and behavior of the supersaturated solutions is given based on various solute species that are formed by the reaction of OH− ions and H2O molecules with normalZnfalse(OH)2 and the subsequent formation of polynuclear zincate species. The rate and extent to which these are formed depends on the availability of OH− ions and unbound H2O molecules at the electrode surface.

The Knoop hardness determinations set forth above (excepting Be~C) were obtained from a paper by Thibault and Nyquist. 4~ Values for Be2C were more recently obtained.The paper under discussion also quotes Knoop hardness readings obtained at both 50-and 25-gram loads on the Tukon tester. In the paper by Thibault and Nyquist 4~ it is pointed out that the Knoop numbers obtained at different loadings are not directly comparable. In order to obtain comparable data, all tests must be conducted at a common load. The cause of the variation of the measured Knoop hardness with indenting load is discussed in a paper by Tarasov and Thibault. 41 ~V[ANLEY W. MALLETT: We wish to thank Mr. Upper for drawing our attention to the fact that Knoop hardness numbers based on indentations made by a 25-or 50-gram load are not directly comparable with numbers determined from indentations mad~ at higher loads. Accordingly, we should revise our statement on the hardness of Be2C to read that it lies between those of zirconium carbide and silicon carbide.

The corrosion rate of zinc in KOH solutions has been measured under a variety of conditions. Amalgamation and the presence of zincate ions lower this rate of corrosion. The effect of increasing KOH concentration on the rate of corrosion is different for nonamalgamated zinc than for amalgamated zinc. The temperature effect is also different for the two types of zinc electrodes.