Maidstone.
P.S.--I always find collodion by DR. DIAMOND'S formula capital, and with
it from five to ten seconds is time enough.
_Mr. Weld Taylor's cheap Iodizing Process._--I have no doubt MR. WELD
TAYLOR will be kind enough to explain to me two difficulties I find in
his cheap iodizing process for paper.
In the first place, whence arises the caustic condition of his solution,
unless it be through the decomposition of the cyanide of potassium which
is sometimes added? and if such caustic condition exists, does it not
cause a deposition of oxide of silver together with the iodide, thereby
embrowning the paper?
Why does the caustic condition of the solution require a larger dose of
nitrate of silver, and does not this larger quantity of nitrate of
silver more than outbalance the difference between the new process and
the old, as regards price? I pay 1s. 3d. for an ounce of iodide of
potassium of purest quality; the commoner commercial quality is cheaper.