Isotopic techniques involving O 1~ have been used to study the cathodic and anodic properties of the oxygen-peroxide couple on partially hydrophobic, active carbon electrodes in alkaline solution. The isotopic analyses have been carried out with an analytical mass spectrometer. For the cathodic reaction, tracer and equilibration experiments prove that all of the peroxide oxygen originates from gaseous oxygen and tha~ the O-O bond is not actually broken in the formation of the peroxide. Tracer experiments also indicate that the oxygen gas liberated during the anodic oxidation of the HO~-ion contains only peroxide oxygen. These results are interpreted in terms of various possible reaction mechanisms. sence of a polarizing current. The over-all electrode reaction in alkaline solution may be represented as follows:O~ -f H20 + 2e ~ OH-q-HO._,-

Rooted cuttings of Rhododendron canescens ''Brook'' and Rhododendron austrinum were grown in sand culture with a modified Hoagland's solution under greenhouse conditions. The effect of varying ammonium : nitrate (NO 3 À : NH 4 þ ) ratios (100 : 0, 75 : 25, 50 : 50, 25 : 75, 0 : 100) on growth, chlorophyll content, plant quality, and elemental tissue concentration were determined. With NO 3 À as the nitrogen (N) form, both azalea cultivars exhibited less vegetative growth, lower overall plant quality, with leaves showing visual chlorotic symptoms in comparison to plants receiving NH 4 þ as the N-form. Leachate pH was highest with NO 3 À as the predominate N-form and decreased significantly with each increment of NH 4 þ . With both azalea cultivars, N-form significantly influenced uptake and utilization of essential plant nutrients. Leaf concentrations of N, potassium (K), calcium (Ca), sulfur (S), boron (B), and molybdenum (Mo) were highest with NO 3 À -N. Leaf elemental concentrations of phosphorous (P), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) increased as NH 4 þ supplied more of the N-ratio. Significant differences in Mg, Mn, and Zn were observed between species. Results from this study show that foliar N concentration is not an accurate indicator of plant growth response. Further investigations are needed to determine if foliarchlorosis and low growth rates observed with NO 3 À fed plants due to an Fe deficiency, to low nitrate reductase (NR) activity in the leaves, or to a combination of these factors.

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Precipitated silicas are carriers for a variety of formulations used in agricultural applications. In such formulations, interaction between the agricultural chemicals and the carriers must be minimized. Precipitated silicas are known to have reactive acid sites on their surfaces, which can cause catalyzed chemical decomposition. An investigation into factors that affect the acid site distribution of precipitated silicas is described in this report. Commercially available and laboratory-prepared precipitated silicas were suspended in isooctane treated with incremental amounts of n-butylamine solution. The distribution of acid sites of different strength was determined by using six Hammett indicators, corresponding to a range of +6.8 to −8.2 pKa, in conjunction with spectrophotometric analysis of the suspensions. Variations in blocking agents, impurities, and salt content are shown to account for alterations in the acid site distribution on the silica surface. Control of these factors will aid the agricultural formulator in minimizing chemical/carrier interaction.