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The results obtained in an investigation of x-ray absorptiometry as a method for the determination of tetraethyllead in gasoline are described. The sensitivity of the absorbance measurements to voltage fluctuations made it imperative to be able to adjust and maintain the primary voltage constant to ±0.10 volt. The refinements necessary to obtain this voltage constancy are given, ap well as other modifications made to the General Electric x-ray

A study of the lower explosion limit of the nitrous oxide-hydrogen system reveals the existence of a minimum in the pressure versus temperature curve for mixtures of any fixed compositions. The addition of molecular oxygen poisons the explosive reaction, and this suggests that the minimum is due to the poisoning of the reaction by oxygen from the thermal decomposition of nitrous oxide. In view of the results of Melville's study of the slow reaction, the mechanism of poisoning must be H + Os + -» H02 + M.After passing through the minimum, the explosion limit does not increase indefinitely as the temperature is raised. Above 900°it decreases again in a vycor vessel, but could not be observed to decrease in quartz vessels of the size employed. In vycor above 900°, the explosion is not strongly affected by added oxygen and this insensitivity would be expected from the interpretation of the low .temperature results.Aberdeen Proving Ground, Md.

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