Vol. 75 concentration is high. The fates of the heptyl radicals must be diverse, possibly leading to various ketones and aldehydes with seven carbon atoms or less followed by hydrogen abstraction by RO. The presence of unsaturation in the products indicates loss of a second hydrogen by heptyl radicals and also a splitting of these radicals with the formation of short alkyl radicals. This type of reaction does not occur appreciably in the gas phase at room temperature but may be aided in solution by the longer possible interval between formation of a heptyl radical and collision with another radical or with, oxygen.It is not useful to speculate further on the mechanism of these reactions in the liquid phase. The results are exploratory and qualitative, and some doubt exists as to whether this type of experimentation can lead to quantitative interpretations in the reaction kinetic sense. ROCHESTER, SEW YORK [CONTRIBUTION FROM THE MCPHERSON CHEMICAL LABORATORY, THEA quantitative study is made of the heterogeneous reaction leading to hydrogen peroxide formation a t light activated zinc oxide surfaces in contact with oxygen, and pure water or water solutions of various organic additives (e.g., sodium oxalate, sodium formate, etc.). The rates and quantum yields of peroxide formation are determined over a range of oxygen pressures, flow rates, times of gas saturation, amounts of zinc oxide in the suspension, additive types and concentrations, times of exposure, and intensities and wave lengths of the light. The ratios of reactants and products of the zinc oxide-water-oxygensodium oxalate system are determined. From the results the following conclusions are made: (1) The often proposed over-all reaction for the irradiated einc oxide-pure water-oxygen system, 2H20 + 02 4 2H202 (I) occurs only to a very limited extent, if a t all.(2) The presence of an additive increases the peroxide formation, but reaction I is not important. The over-dl reaction in the system containing sodium oxalate additive is shown to be:It is shown that the product hydrogen peroxide is decomposed under certain conditions. In general in the additive-containing system the light-activated zinc oxide catalyzes the occurrence of a normally exothermic reaction.A number of chemical reactions are promoted in systems containing irradiated zinc oxide. For example, zinc oxide in contact with silver oxide gives silver and oxygen among other products.aa-d Also previous investigations have shown that hydrogen peroxide is formed at light-activated zinc oxide surfaces in contact with oxygen, water and miscellaneous ~~m p o u n d s .~~-~ Although no detailed quantitative studies of this heterogeneous reaction have been made, the often proposed over-all reaction4 of peroxide formation is 2H20 f 0 2 + 2He02. Since reaction (1) involves a large increase in free energy ( A E h = 25 kcal./mole H&) the zinc oxide-water-oxygen system is attractive as a possible converter of light energy to chemical energy. The light absorption region of zinc oxide limits the effective wave...

drops of concentrated sulfuric acid and 10 ml. of hydrofluoric acid (48%). This is heated until dry, ignited, cooled, and weighed. The difference in weight represents silica.Any residue left in the platinum crucible is fused with potassium acid sulfate, the mass dissolved in hydrochloric or sulfuric acid (1 to 9), and the contents are added to the combined original filtrates which should have a total acidity of 10 to 20% and a total volume of not more than 250 ml. The required amount of halomandelic acid is now added and the zirconium content of the sample determined as described above.Results obtained by this procedure are given in Table III. SUMMARY Zirconium in aluminum alloys can rapidly and conveniently be 'determined gravimetricaliy by the mandelate method. The use of p-chloroor p-bromomandelic acid is preferred to mandelic acid (4). No significant difference exists between the chloro and bromo derivative. These reagents are now available com-mercially from the H.

the positions of several anomalous spectral lines. In 1875 de Boisbaudran^ reported the actual separation of a small quantity of the element. Its physical properties were found to be very close to those predicted by Mendel eeff. The new element was named after the country in which it was discovered-Gaul (France). Gallium is dis-3 6 tributed widely, * although in very small amounts (never (6) E. Einecke, "Das Gallium," Leipzig, Verlag von Leopold Voss, 1937. more than 0 .01$ in any material) over the whole of the earth's crust. It occurs in greatest concentration associated with the ores of aluminum, zinc and germanium. Pure, solid gallium is silvery white in appearance, and, on melting at 29.75°C., is very similar to liquid mercury. Gallium has a strong tendency to wet materials such as glass. Its very great alloying ability^*^ causes (7) Atomic Energy Commission, "Liquid Metals Hand book," Washington Govt. Printing Office, 1950.

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