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Contrary to the results of previous investigators, it has been found that molecular O2 and N2 have no effect on the ductility of rock salt single crystals. Also, it has been found that air-aged crystals are brittle in summer and are ductile during a major fraction of the time in winter. Ductile rock salt crystals have been made brittle by subjecting them to ozone, NO, and atomic oxygen atmospheres. It is believed the ozone content of the atmosphere is responsible for the reported effects on brittleness. Other embrittling agents have been found.
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Machlin et al. (1959) studied this question.
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