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HAROLD S. JOHNSTON, L o u m FOERING A N D R. J. THOMPSON
esting t o note the “hash” of fine structure which occurs under certain conditions. This is strongly suggestive of a similar type of phenomenon which is sometimes observed in powder driven rockets. The authors suggest that this evenly-spaced fine structure is due to a type of acoustic resonance occurring within the reaction chamber and have taken precautions to damp it out by suitable means. However, it would seem that if this is the explanation one would expect the resonance frequency to be pressure dependent and, to a first approximation, vary as the square root of the pressure. Since apparently t,his is not the case one might conclude that either the resonance is due to the excitation ot some low frequency mode of the experimental equipment, or it is a real manifestation of the reaction. N. DAVIDSON (California Institute of Technology).-Dr. R. Ogg of Stanford has suggested the possibility that the ignitions observed in this paper are initiated by hydrogen atoms formed in the initial step of the alkali metal, water reaction. I have no objection t o this interesting possibility, but we should inquire whether there are other possible explanations. Is it certain that the observed explosions are not initiated thermally? For reactor I, with the large excess of water, the heat ok reaction, if uniformly distributed, cannot raise the temperature very much, but there might be local hot spots where the hydrogen-oxygen explosion is initiated. I n reactor 11, there is only a slight excess of water; the adiabatic reaction temperature might be quite high. I n Table 11, for the experiments with oxygen absent and no explosion, the maximum transient pressure increase is four and a half times the calculated pressure increase for an isothermal reaction. There was an additional initial pressure of one atmosphere of nitrogen. Depending on whether or not the stoichiometric excess of water vaporizes, t,hm indicates an increase in absolute tem erature by a factor of 1.2 or 2.5, i.e., from 300 to 360 B or 750°K. The latter temperature might be great enough to initiate explosion. M. I
