CHLORIDE OF SILVER.--This salt of silver, whether in its precipitated
state, or when fused, changes its color to a fine bluish grey by a very
short exposure to the sun's rays. If combined with a small quantity of
nitrate, the change is more rapid, it attains a deep brown, then slowly
passes into a fine olive, and eventually, after a few weeks, the
metalic silver is seen to be revived on the surface of the salt. Great
differences of color are produced on chlorides of silver precipitated
by different muriates. Nearly every variety in combination with the
nitrate, becomes at last of the same olive color, the following
examples, therefore, have reference to a few minutes exposure, only, to
good sunshine; it must also be recollected that the chloride of silver
in these cases is contaminated with the precipitant.

Muriate of ammonia precipitates chloride to darken to a fine chocolate
brown, whilst muriate of lime produces a brick-red color. Muriates of
potash and soda afford a precipitate, which darkens speedily to a pure
dark brown, and muriatic acid, or aqueous chlorine, do not appear to
increase the darkening power beyond the lilac to which the pure
chloride of silver changes by exposure. This difference of color
appears to be owing to the admixture of the earth or alkali used with
the silver salt.

The prismatic impression on paper spread with the chloride of silver is
often very beautifully tinted, the intensity of color varying with the
kind of muriate used. Spread paper with muriate of ammonia or baryta
and you obtain a range of colors nearly corresponding with the natural
hues of the prismatic spectrum. Under favorable circumstances the mean
red ray, leaves a red impression, which passes into a green over the
space occupied by the yellow rays. Above this a leaden hue is
observed, and about the mean blue ray, where the action is greatest, it
rapidly passes through brown into black, and through the most
refrangible rays it gradually declines into a bluish brown, which tint
is continued throughout the invisible rays. At the least refrangible
end of the spectrum, the very remarkable phenomenon has been observed,
of the extreme red rays exerting a protecting influence, and preserving
the paper from that change, which it would otherwise undergo, under the
influence of the dispersed light which always surrounds the spectrum.
Not only the extreme red ray exerts this very peculiar property, but
the ordinary red r