A number o£ experimental results are presented which show the variation of the pH values o£ several soils when samples of each are shaken with CaCl 2 solutions of different concentrations.These results are then interpreted on the basis of the ratio law-derived from the Gouy theory of the electrical double layer -and it is shown that the pH values and electrolyte concentrations show the expected relationship, provided the latter is not too large.The importance of the connection between pH and electrolyte concentration in the routine measurement of soil pH is emphasized, and it is pointed out that such measurements must be carried out using an electrolyte solution of known composition in order to obtain comparable results from different soils.It has been found that 0.01 M CaCl 2 is the most satisfactory for use in normal non-saline soils where the surface density of electrical charge on the colloidal material is high and independent of the solution composition: this electrolyte concentration is such that measurements made with the usual glass electrode/saturated calomel cell give accurate and reproducible values which are largely independent o£ the soil/solution ratio, and is yet sufficiently dilute to allow a satisfactory calculation of the "lime potential" characteristic of the soil sample.

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Compositions of solutions equilibrated with the salts at 25°C yielded the solubility products 7.1 x 10-14 for MgNH4P04 . 6H2O and 2 4 x 10-11 for MgKPO4 . 6H2O. Both salts dissolve incongruently in water with precipitation of trimagnesium phosphate. Conditions are defined for the precipitation of MgNH4P04 .6H2O without contamination with trimagnesium phosphate.Although the precipitation of MgNH4P04 .6Hz0, is a well-known analytical procedure, no measurement of its solubility product has been reported. The value of 2.5 x 10-13 reported by Bube 1 is based upon an estimate that the compound dissolves congruently in water to give a 1 x 10-3 M solution. The preparation of the analogous potassium compound, MgKP04.6H20, was described by Agte et aZ.2 and by Bassett and Bedwell,3 but there are no data on its solubility.Measurements were made of the solubility products of each compound in experiments designed to establish the conditions under which it dissolves congruently.

The vertical fluxes of alachlor, atrazine, simazine, and toxaphene were measured by air-sampling and aerodynamic measurements over a 24-day period after surface application to a fallow soil in eastern Maryland. The triazines were applied at 1.68 kg/ha as a wettable powder formulation and alachlor and toxaphene at 2.24 and 2.52 kg/ha, respectively, as emulsifiable concentrates. Calculated volatilization losses in the first 21 days were 780 g/ha toxaphene, 420 g/ha alachlor, 40 g/ha atrazine, and 21 g/ha simazine. Daily losses varied with soil moisture content, alachlor and toxaphene volatilization being reduced as the surface soil layers became dry. Daily volatilization patterns of atrazine and simazine indicated that some wind erosion of wettable powder formulation occurred as the surface soil dried, but the amounts transported were small. Volatilization losses of triazines were much smaller than disappearance by chemical degradation. A simple empirical equation was shown to yield estimated volatilization rates that were within about a factor of 10 of field-measured rates for six of eight compounds whose vapor pressures spanned a range of 104.

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