of every photographer. Distilled water should always be used in the
preparation of emulsion, as the impurities of ordinary water may often
introduce disturbing conditions.--_Photographic News_.

[Illustration]

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BLACK PHOSPHORUS.

By P. THENARD.


The author refers to the customary view that black phosphorus is
merely a mixture of the ordinary phosphorus with traces of a metallic
phosphide, and contends that this explanation is not in all cases
admissible. A specimen of black or rather dark gray phosphorus, which
the author submitted to the Academy, became white if melted and remained
white if suddenly cooled, but if allowed to enter into a state of
superfusion it became again black on contact with either white or black
phosphorus. A portion of the black specimen being dissolved in carbon
disulphide there remained undissolved merely a trace of a very pale
yellow matter which seemed to be amorphous phosphorus.--_Comptes
Rendus_.

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