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 ray through nearly its whole length.

In photographic drawing this salt is of the utmost importance.
Mr. Talbot's application of it will be given hereafter in another
portion of this work.

IODIDE OF SILVER--Perfectly pure, undergoes very little change
under the influence of light or heat; but if a very slight
excess of the nitrate of silver be added it becomes infinitely
more senitive than the chloride

The spectrum impressed upon paper prepared with a weak solution of
the hydriodate of potash presents some very remarkable peculiarities.