ver plate at a temperature of 45 deg. or less,
exposed to the vapors of iodine, is less sensitive and takes a longer
time to coat, than when it is at a temperature of 60 deg. or more.

Whenever a view is to be taken, or any impression which requires the
plate to be turned on the side, it should be buffed in the other
direction, so that the marks will always be horizontal, when the
picture is in position. With the finest possible polish, the plate is
ready for the coating box.

The question is often asked by operators, what is the state of the
plate when polished and allowed to stand for a time before using? To
meet this point we hare only to consider the silver and the power
acting upon it. Pure atmosphere does not act upon silver; but we do
not have this about in our operating rooms, as it is more or less
charged with sulphurated hydrogen, which soon tarnishes the surface of
the plate with a film of brown sulphurate. It is this that sometimes
causes the specks which appear on finishing the impression, and are a
great annoyance. Hence we see that the plate should be buffed just
before receiving the vapor of iodine. Mr Hunt gives his opinion of the
use of diluted nitric acid as the best solution for freeing, the
surface of the plate; he says:

"Numerous experiments on plated copper, pure silver plates, and on
silvered glass and paper, have convinced me that the first operation of
polishing with nitric acid, etc., is essential to the production of the
most sensitive surface. All who will take the trouble to examine the
subject, will soon be convinced that the acid softens the silver,
bringing it to a state in which it is extremely susceptible of being
either oxydized or iodized, according as the circumstances may occur of
its exposure to the atmosphere or the iodine."

I cannot see the objection to this solution; not, however, in general
use. Our operators do not find it of sufficient importance to the
success of their pictures to accept it, the alcoholic solution being in
its nature less objectionable.

I will say here, that a plate submitted to only an ordinary polish is
found to contain numberless minute particles of the powder made use of.
Should the same plate be buffed for a long time, the polish will nearly
all disappear, leaving the cavities in the surface free for the action
of agents employed in subsequent operation. For this reason, I find
that great amount of polishing powder should not be appl