ON  THE  CHANGE  OF REFRANGIBILITY  OF LIGHT.
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150.    Hydrate of Peroxide of Uranium.—Some crystallized nitrate of uranium was exposed to a heat a good deal short of redness, whereby most of the acid was expelled.    The residue was of a deep brick-red colour, and consisted  no  doubt  chiefly of anhydrous peroxide.   It was quite insensible.    In order to remove any undecomposed nitrate, it was boiled with water, whereby the undecomposed nitrate was dissolved, and the peroxide converted into  a hydrate.    This  hydrate, after  having  been washed and dried at the temperature of the air, was of an extremely beautiful yellow  colour,  and  was   I   suppose   the  hydrate  IPO3 4- 2HO described in chemical treatises.    It was tolerably sensitive, in fact for an inorganic substance extremely so, though the sensibility was much less than that of nitrate of uranium, yellow uranite, or canary glass.   The derived spectrum consisted as before of separate bright bands.    A small portion of the powder was attached by water to blotting-paper, and dried before a fire.    The powder thus obtained on paper was duller than before, and inclined a little more to orange, though the colour was not much deeper than that of the former hydrate.    From its colour and the circumstances of its formation, it was probably the other hydrate U203-fHO.    It proved on examination to be totally insensible.
151.    Acetate of Peroxide of Uranium, prepared by dissolving the yellow hydrate of the peroxide in acetic acid, and evaporating to crystallize.—This salt is extremely sensitive, about as much so as  the  nitrate.    The derived spectrum consisted of six  bright bands arranged at regular intervals.    It seemed to me that the last five of these were respectively a little more refrangible than the five bands given by the nitrate, and then a sixth band was visible in the faint red in the case of the acetate which was not ordinarily seen in the  nitrate.    However, this  observation has need to be repeated under more favourable circumstances.
152.    Nitrate  and  acetate  of peroxide   of uranium,  yellow uranite, and canary glass, are all so highly sensitive as to allow the   primary spectrum  to  be  examined with a  prism at  some distance.    In the first three media the bright bands are narrow, much narrower than the dark intervals between;   in the glass they appear much broader than in the other media.
153.    Oxalate of Peroxide of Uranium, prepared in the manner mentioned by M. Peligot, namely, by adding a saturated solution
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