_Deepening Collodion Negatives._--I have lately been trying a method of
deepening collodion negatives, so as to render instantaneous impressions
capable of being printed from, which I have found to answer admirably;
{283} and although it is but a slight modification of MR. LYTE'S process
described in "N. & Q.," it is a very important one, and will be found to
produce far better results. The picture having been developed in the usual
way, with a solution of pyrogallic acid, is whitened by means of MR.
ARCHER'S solution of bichloride of mercury. The plate is then washed with
water and a solution of _iodide of cadmium_ poured on. This converts the
white chloride of mercury, which constitutes the picture, into the yellow
iodide, in the same manner as the solution of iodide of potassium
recommended by MR. LYTE; but is much to be preferred, as it produces a more
uniform deposit. The solution of iodide of potassium dissolves the iodide
of mercury as soon as it is formed, and therefore cannot be left on the
plate until the decomposition of the chloride is complete, without injury
resulting to the picture, as the half-tones are thereby lost, and those
parts over which the solution first flows become bleached before the other
parts have attained their highest tone; whereas the solution of iodide of
cadmium may be allowed to remain for any length of time on the plate,
without any fear of its injuring the negative.