an alkaline _mellonide_ arsenite, etc. Sulphureted hydrogen, or a
sulphide, will give a _brown_, or _black_ tone, which may be protected
against oxygen and dampness by a resinous varnish.

"Of all the simple pictures obtainable with bichromated papers, without
complications or other tonings, those obtainable by the combination of a
salt (say the sulphate) of _manganese_, with the bichromate in the paper
preparation, are about the best; these pictures being, however, capable of
being toned and modified in many different ways if desired. This may be
accomplished by the use of toning baths of ferridcyanide or ferrocyanide,
or other metal cyanogen salts, etc., or by either mixing the salts of
other metals, as copper or iron, with the cyanic toning baths, or using
them in the original solution, or by soaking the paper in them, as in
Sella's process, previously to the application of the metal cyanic,
mellonic or other toning baths. Alkalies and alkaline carbonates may also
be used to remove the chromic acid, and leave a subsalt, or the very
stable oxide or carbonate of manganese, which may be peroxidized by the
use of chloride of lime, peroxide of hydrogen, or ozone."

"In all the processes with metallic salts, alone with bichromates, the use
of sized or unsized paper along with gelatine, etc., has some advantages.
I have got good results by such processes on albumen paper, the albumen
tending to prevent mealiness in the print; also on paper soaked in
gelatine before the application of the bichromic solution. * * * There is
great interest connected with the action of all such papers, along with
the tannin and vegetable coloring matters. I have long been of opinion
that by the steeping of papers or textile fabrics, containing the salts
not only of iron, as recommended by Mr. Sella, but of tin, copper,
bismuth, lead, etc., in solutions of cochineal, red cabbage, beetroot,
grass or the most ordinary foliage, etc., that the most useful results
might be obtained; though for _certain_ permanence I am not sure but that
some of the other processes which I have briefly run over with the
cyanogen acid salts or metallic acid salts, as precipitators, may be more
to be depended upon. The processes with _precipitated oxides_, such as
the one with manganese and similar ones, with other metals which I have
described, I also consider as deserving of more attention than almost any
processes which have been stated, on the score of probable