Technical Digests: An Interesting Application of Electron Diffraction

O I L I C O S I S develops rather quickly in rabbits exposed to air con^ taining moderate concentrations of quartz particles finer than about 5 X 10 -4 cm, but is completely prevented if aluminum powder is also present in the air to the extent of about one per cent by weight of the quartz powder. This protective action of aluminum powder was discovered at the Mclntyre-Porcupine Mines, and has been studied experimentally by Denny, Robson and Irwin. 1 It has been established t h a t aluminum forms, in the lungs, a protective film upon the surface of silica particles which prevents them from dissolving, and thus prevents toxic effects. From the relative amounts of aluminum and silica, and diameters of silica particles, one can deduce that this protective film need never be so thick, on the average, as 2 X 10~8 cm, and is, in general, many times thinner than this. The action of the aluminum is sufficiently striking and important to justify a fuller understanding of the nature of the film which it forms upon quartz particles and Dr. Frary, Director of the Aluminum Research Laboratories, suggested to us that the answer might be forthcoming through a study of electron diffraction patterns. In our experiments, electron diffraction patterns were obtained from thin films of silica, about 2 X 10~6 cm thick, which had been previously treated with water containing metallic aluminum powder. A beam of high speed electrons was sent through such a treated film and the resulting diffraction pattern recorded upon a photographic plate.