_Improvement in Collodion._--As there are many photographers who are not
members of the Photographic Society, and who do not see the journal
published by that body, a statement of what I think will be found a very
material improvement in the manufacture of collodion may not be
unacceptable to the readers of "N. & Q." To five drachms of pure _washed_
ether, add one drachm alcohol 60deg over proof, and dissolve therein
sufficient soluble cotton to make it of the consistence of oil (the exact
quantity must depend rather upon the dexterity of the operator, as the
thicker it is the more difficult to use) then add twenty minims of
chloroform, dropping in the latter, which will fall to the bottom, but is
readily dissolved on shaking the mixture for a few minutes.
To two drachms of the same alcohol add the iodizing material preferred, and
mix with the other ingredients.
The above will be found to flow very evenly smoothly over the plate; is
tough, intense, and _structureless_ in appearance. I have not yet
determined what is the best iodizing mixture, but at present I prefer
iodide of potassium _alone_, if pure, and twenty grains to the ounce of
alcohol is the proportion I generally adopt; thus having five grains in
each ounce of collodion.
Lastly, as regards the soluble cotton, I cannot find any better material
than that produced according to the formula published by Mr. Hadow, in the
March Number of the _Photographic Journal_, thus: "Take of nit. potash,
five parts; sulphuric acid, ten parts; water, one part; _all by weight_.
Add the water to the nitrate of potash, and then the acid, and immediately
immerse as much cotton wool as can be thoroughly saturated by the mixture,
leaving it in for _at least_ ten minutes, and wash with a great abundance
of water. The object of adding the cotton immediately that the acid has
been mixed with the nitrate of potash, is to expose it to the action of the
chemicals while they are at a temperature of from 120deg to 130deg. For
farther particulars on this head, I must refer to Mr. Hadow's paper.