ed by silver nitrate form a brick-red
precipitate of some opacity.(34)

Chloride of nickel and potassium ferrocyanate produce a fine brown.

Lime water and alizarine dissolved in alcohol dye violet.

Alizarine and the caustic alkalies produce a variety of tints, from violet
to purple, according to the concentration of the solutions.

Lead acetate and alizarine in ammoniacal solution dye purple.

Potassium ferrocyanide and uranium nitrate produce a warm sepia tone. With
chloride of nickel the tone is brown.

Ammoniacal solution of coralline diluted with water gives carmine red.

Potassium bichromate and extract of indigo produce a fine greenish tone
suitable for landscapes.

Extract of indigo colors blue(35)

Some of these reactions can be applied to the printing processes with the
bichromates, etc. The paper should be coated with galatine. See the
Appendix.

Other colorations can be obtained with dyes in utilizing (as shown by
Persoz) chromous chromic oxide as a mordant: alizarine, Brazil and yellow
wood (morus tinctoria), Fustet (rhus cotinus), etc. The extent of this
work does not admit of describing the numerous processes which can be
employed; they will suggest themselves to the chemist.

The alkalies employed with the dyes should be employed in diluted
solutions, as being liable to produce reticulation. By applying the
coloring matters and the mordants thickened with a little starch, the
image can be colored with different colors. Lantern slides can be thus
colored with great ease.

PREPARATION OF RED, YELLOW, OR BLUE TISSUES.

_Red Tissue.--_Dissolve 10 grams of carmine in 1 liter of aqueous ammonia
and evaporate. When the smell of the alkali has almost disappeared, add 1
liter of rain water. Of this take 65 cubic centimeters, add 35 c.c.m. of
rain water, and in the solution let soak for an hour 15 grams of very
soluble gelatine, add 1 gram of sugar, and dissolve in a water bath.
Filter, and take of the mixture a sufficient quantity (25 c.c.m. for a
surface 18x24 centimeters) to cover a sheet of paper which has been
previously applied upon a glass plate in the following manner: In a tray
full of hot water, immerse the plate and the paper; remove the whole in
such a manner as the paper remains in contact with the plate; rub out the
excess of water with a squeegee, and flow the gelatine over the paper
still damp. Let cool on a leveled stand, and when the gelatine is
solidified to a consi