The solubilities of the red and yellow forms of lead monoxide, of hydrated lead monoxide and of basic lead carbonate in dilute aqueous potassium hydroxide solutions at 25°have been determined.The change of the stoichiometrical equilibrium constant with concentration shows that the activity coefficient of the plumbite ion is about the same as that of the nitrate ion in dilute solutions.From the extrapolated values of the equilibrium constants, the free energies of solution have been calculated.

The principal factor determining the sharpness of the electrometric end-point with polarized electrodes of pure platinum is the difference in the degree of reversibility of the electrode reaction before and after the end-point. Other factors such as concentration and rate of stirring are of minor importance. The end-point phenomena are more distinct, the more nearly the electrode reactions conform to the requirement of complete reversibility on one side of the end-point and complete irreversibility on the other, but are sharp enough for practical use in analysis in some cases which fall far short of meeting this requirement.2. Although the polarization sometimes produces a slight displacement of the end-point break of a single electrode, the errors so introduced are generally too small to be of significance in a volumetric analysis.3. The end-point break in titrations of the ordinary type, based on the single potential of a platinum electrode, may often be improved and the behavior of the electrode made much more dependable and satisfactory by polarizing it with respect to an auxiliary electrode.

Accurate values for the dimensions of crystal lattices are becoming increasingly important and necessary and the X-ray examination of crystals is probably the best method for obtaining these values. This paper is a report of precision X-ray measurements on some of the alkali and ammonium halides. The ammonium halides have not been subjected to precision measurement, although Bartlett and Langmuir,1 and Vegard2 have published values for the cube sides which are in fair agreement. Davey3 has reported precision measurements upon all of the alkali halides, but it seems desirable to repeat a part of his work with salts of known purity. Experimental PartApparatus.-We have employed the photographic powdered-crystal method. The K-a doublet of molybdenum, with a mean wave length of 0.710 A. U., was the line recorded on the diffraction patterns. Two cameras were used. The first is similar to that of Wyckoff at the Geophysical Laboratory. Its film radius is 15 cm. and to produce a nearly parallel beam of X-rays, a slit system composed of two gold slits, 15 cm. apart, is provided. With this camera, the lines on the diffraction pattern are very fine. The second camera is similar to the casset used by Davey4 except that a full semicircle is used, with the zero beam striking the film in the middle. The film radius is 16.5 cm.,

The previous papers1 2in this series of investigations have shown that the growth ratios of potassium and ammonium alum crystals are greatly modified when grown in the presence of dyes and other foreign substances. Thus potassium alum, when grown in the presence of diamine sky blue develops into perfect cubes having no octahedral faces. The cube faces alone are colored and the growth ratio [ioo]/[iii] undergoes a change from 1.61 to o.o in a dye concentration of 0.1%.These effects have been accounted for on the basis of (i) the residual valency force fields of the crystal planes; (2) the interionic distances within the faces; and (3) the presence and distribution of polar groups in the adsorbed material.

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