solution, a blue print is obtained. Bichromate prints can be made on
albumenized paper by floating it on the solution, and by using a
saturated solution of protosulphate of iron and a saturated solution of
gallic acid. Very fine prints can be so produced nearly equal to silver
prints, and at somewhat less cost, but with a little or no saving of time
or labor.

_Chief Proof Solution_.--If old oxalate developer be exposed in a shallow
vessel in a warm place, a deposit of light green crystals will be formed,
composed of an impure oxalate of iron. If these crystals be dissolved in
water, and paper washed with a strong solution, when dry it may be
exposed in the printing-frame, giving full time. The image is very faint,
but on washing in or floating on a moderately strong solution of red
prussiate of potash for a minute or less, a blue positive is produced,
which is washed in water as usual to fix it. The unused developer
produces the best crystals for the purpose, and the pure ammonio-oxalate
is vastly better than either.

All of the above operations, except the printing, should be carried on in
the dark room, or by lamp or gas light only. The solutions and the paper
should also be kept in the dark, and prepared as short a time as possible
before use.


II. COMPOUND NEGATIVES.

In photographing with the microscope, it frequently occurs that the
operator, instead of devoting a negative to each of two or more similar
objects for comparison, printing both upon the same print, prefers to
have the whole series upon one negative, and taking from this a single