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...

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mechanics as an approximate theory adequate for the description of the motions of large scale bodies, but admittedly inadequate for atomic and sub-atomic motions. Too much attention to conclusions based on advanced research is to be deprecated as confusing, but an occasional glimpse of the problems and results of the new physics will surely be stimulating to interest and imagination.The most important connection between the new physics and secondary school teaching is probably the indirect effect which study of the quantum theory should have on the mental attitude of all teachers of elementary physics toward their work. We should all relearn the necessity of approaching nature with an open mind, sharply differentiating theory from fact, and following the evidence wherever it leads without regard to our preconceptions. Physics taught in this spirit, whether in school or college, will be the truly cultural subject which it ought to be.The last address was by Dr. Alfred V. Kidder of the Carnegie Institution. He spoke upon the Indians of North America and the Mayan Civilization. The talk was somewhat informal and illustrated profusely with beautiful lantern slides. Dr. Kidder told in detail of the restoration of some of the Mayan Temples and with his first hand knowledge gave us a most interesting insight into the trials and triumphs of this branch of historical research. The Secretary regrets that it is not possible to publish the address in full.The authors wondered if some of the chemistry topics that are usually presented to high school and freshman college students could be rated according to their degree of difficulty in understanding; and also if the topics ranked in the same order according to their degree of difficulty in presentation. Further, whether the boys would rate the topics the same as the girls, and the high school students the same as the college students.In order to ascertain the ratings twenty topics were submitted to more than five thousand high school and freshman college students of chemistry in seventy different schools. The students were asked to rate the topics according to the degree of difficulty they had in understanding them, and the teacher was asked to rate the same topics in the order of difficulty in presentation to students.The topics were divided into two groups. The first group consisted of fundamental ideas and theories of a broad character upon which the science of chemistry is built. The second group contained topics of useful ideas of a-more specific nature that support the general topics in Group I. It was impossible to make a clear cut distinction between the'groups, or to group, word, and select the topics in such a way that-everyone should agree.