Considerable experimental work has been recorded in the literature on the curious and as yet unexplained coagulating action of ultra-violet, p-, and X-rays on substances in the colloidal state.l Extraordinary 2s this effect appears, the case is still more complicated by the fact that these same rays have been employed by many investigators to produce certain hydrosols from the corresponding metals.2 Moreover in some respects the evidence of one author often contradicts the results obtained by

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... hers, so that the entire subject is in a decidedly unsatisfactory state.