_New Process for Positive Proofs._--I have tried a method of preparing my
paper for positive proofs, which, as I have not seen it mentioned as
employed by others, and the results appear to me very satisfactory, I am
induced to communicate to you, and to accompany by some specimens, which
will enable you to judge of the amount of success.
I use a glass cylinder, with air-pump attached, such as that described by
MR. STEWART as employed by him for iodizing his paper. I put in this the
salt solution, and that I use is thus composed: 2 drachms of sugar of milk,
dissolved in 20 ounces of water, adding--
Chloride of barium 15 grs.
Chloride of sodium 15 grs.
Chloride of ammonium 15 grs.
In this I plunge several sheets of paper rolled into a coil (taking care
that they are covered by the solution), and exhaust the air. I leave them
thus for a few minutes, then take them out and hang them up to dry; or as
the sheets are rather difficult to pin, from the paper giving way, spread
them on a frame, across which any common kind of coarse muslin or tarletan,
such as that I inclose, is stretched.
I excite with ammonio-nitrate of silver, 30 grains to 1 ounce of water,
applied with a flat brush.
I fix in a bath of plain hypo. of the strength of one-sixth. The bath in
which the inclosed specimens were fixed has been in use for some little
time, and therefore has acquired chloride of silver.
I previously prepared my paper by _brushing_ it with the same salt
solution, and the difference of effect produced may be seen by comparing a
proof so obtained, which I inclose, with the others. This latter is of
rather a reddish-brown, and not very agreeable tint. I have inclosed the
proofs as printed on paper of Whatman, Turner, and Canson Frères, so as to
show the effect in each case. The advantages which the mode I have detailed
possesses are, I think, these:
Greater sensitiveness in the paper,