but only to a partial extent.
Theoretically, the method is not so good as sulphide proper; it is much
more inconvenient in practice except on a commercial scale, while the
results cannot be said to quite equal those by the sulphide process as
regards permanency.

So much by way of theory. We will now give the formulae for the two
solutions required in the sulphide process. The first of these is the
"bleach," or oxidizing mixture of bromide and ferricyanide. Within
reasonable limits, the proportions of these salts and the quantity of each
in the solution does not matter very much. Each chemical can, if desired,
be kept in a separate solution if care be taken to keep the mixture in the
dark,--that is, in a cupboard where it will not be exposed constantly to
daylight. The ferricyanide suffers in time by exposure to daylight; but,
as both it and the bromide are comparatively cheap and serve for a large
number of prints, there is no need to take excessive care. The
ferricyanide-bromide mixture, however, keeps very much better than a plain
solution of ferricyanide alone. Formulae which place the salts in separate
solutions are a mistake.

As good a formula as any is: Potass ferricyanide, 300 grains; potass
bromide, 100 grains, water 20 ounces; Ammonium bromide may be used in
place of the potassium salt in the above formula; the difference is not
marked, but the ammonium compound tends to give a somewhat warmer brown or
sepia. In the case of many formulae, it will be noticed that equal
quantities of bromide and ferricyanide are recommended. Although, as just
stated, variations in the formula are not at all marked in their effects,
a proportion of bromide over one-quarter of the ferricyanide does tend
towards the yellowish color of which complaints are now and again heard. I
want to make it clear that the opportunities for going wrong with the
bleacher are very small indeed. Without encouraging the reader to be
careless let it be said that "any old formula" (of ferricyanide and
bromide) for the bleacher will prove successful. Not so, however, in the
case of the sulphide solution, which requires to be very carefully made up
and used.

Sulph_ide_, not sulph_ite_. The material for the toning or darkening of
the bleached print is the chemical substance, sodium sulphide, of the
formula Na_2S.9H_2O. This is purchased as small crystals which greedily
absorb water and rapidly become almost liquid if not properly corked. Not
that thi