CHAP. III.

SYNOPSIS OF MR. HUNT'S TREATISE ON "THE INFLUENCE OF THE
SOLAR RAYS ON COMPOUND BODIES, WITH ESPECIAL REFERENCE TO
THEIR PHOTOGRAPHIC APPLICATION."


OXIDE OF SILVER exposed for a few hours to good sunshine,
passes into a more decided olive color, than characterises it
when first prepared by precipitation from nitrate of silver.
Longer exposure renders this color very much lighter,
and the covered parts, are found much darker, than those on which
the light has acted directly. In some instances where the oxide
of silver has been spread on the paper a decided whitening
process in some parts, after a few days exposure, is noticed.
Oxide of silver disolved in ammonia is a valuable photographic fluid;
one application of a strong solution forming an exceedingly
sensitive surface. The pictures on this paper are easily fixed
by salt or weak ammonia.

NITRATE OF SILVER.--This salt in a state of purity, does not appear
to be sensibly affected by light, but the presence of the smallest
portion of organic matter renders it exceedingly liable to change
under luminous influence.

If a piece of nitrated paper is placed upon hot iron,
or held near the fire, it will be found that at a heat just