_A Hint to the Photographic Society._--It has been objected to this
Society, that beyond the establishment of its _Journal_, and the forming of
an Exhibition, it has done very little to promote the improvement of the
beautiful art it was specially intended to advance. Such objections are
very easily urged; but those who make them should at least propose a
remedy. It is in no unfriendly spirit that we allude to these complaints;
and we well know how difficult it is for a body like the Photographic
Society to take any important step which shall not be liable to
misconstruction. We would however suggest, that among those endeavours
which it would become the Society to make, there is one which might at once
be taken, namely, to secure for the photographic public a good paper. The
want of such an article is hourly felt. If the Photographic Society,
following the example of the _Society of Arts_, should appoint a Committee
to take this matter into consideration, to define clearly and unmistakeably
the essentials of a good _negative_ paper for calotypes (for perhaps it
would be well to keep to a _good negative_ paper), and offer a premium for
its production, a very short time would elapse before specimens of such an
article would be submitted for examination. It is clear that the premium
need be one only of small pecuniary value; for the fact of a maker having
produced such an article as should gain the prize, would secure him an
ample recompense in the enormous demand which would instantly arise for a
paper which should be stamped with the public approval of a body entitled
to speak with so much authority on such a subject as the Council of the
Photographic Society.
_Test for Nitrate of Silver._--The READER OF PHOTOGRAPHIC WORKS, who in
Vol. ix., p. 111., asked for information as to how he might know whether
nitrate of silver was pure, can detect any impurities with which that salt
is likely to be contaminated, by applying a few simple tests to an aqueous
solution of it. The impurities which nitrate of silver most frequently
contains are nitrate of copper, nitrate of potash, and free nitric acid. It
is also sometimes intentionally adulterated with nitrate of lead. The
presence of a salt of copper is detected by the solution assuming a blue
colour when mixed with an excess of ammonia. To detect nitrate of potash,
hydrochloric acid should be added to the solution in sufficient quantity to
precipitate the whole of the silver. The liquid should then be freed from
the precipitate by filtration, and evaporated; if nitrate of potash is
present, a fixed residue will remain after evaporation. The presence of a
salt of lead is detected by adding a few drops of sulphuric acid to the
solution of nitrate of silver, which precipitates the lead as sulphate if
present. It is, however, necessary to dilute the acid with a considerable
quantity of water, and, if any precipitate forms, to allow it to subside
previous to using it as a test for lead, as ordinary sulphuric acid is
frequently contaminated with sulphate of lead, which is soluble in the
strong, but not in dilute, acid.
Any free nitric acid in the nitrate of silver can be detected by the smell.
The crystals can be freed from {182} it, should they contain any, by fusing
them in a porcelain crucible over a spirit-lamp. The ordinary fused lunar
caustic of the surgeon is unfit for general use as a photographic agent.