ring the immersion. When the fibers are well imbued, which
requires from four to five minutes, remove the calico with the glass rod
and rinse it thoroughly in water. This done, wring out the superfluous
liquid as much as possible, and, finally, immerse each piece separately in
a solution of

Sodium nitrite, 7 parts
commercial
Hydrochloric acid, 16 parts
commercial
Water 100 parts

After turning the pieces of calico two or three times over, they are
rinsed to eliminate the acid, then drained and placed between sheets of
blotting paper to dry. All this, except the impregnation with primuline,
should be done in the dark room.

As said above, primuline is transformed by nitrous oxide into a diazotized
compound, and consequently the material is now susceptible of being acted
on by light. It does not keep, and should be exposed, etc., soon after
its preparation.

Paper is impregnated with primuline either by floating or brushing. The
best results are obtained with paper previously sized with arrowroot or
gelatine in order to keep the image entirely on the surface of the paper.

Linen, silk and wool are treated as calico.

The cliches should be positive to obtain positive expressions and somewhat
more opaque than those employed in the processes before described, else
vigor and intensity could not be obtained. Here we must state that the
primuline process seems to be better adapted for the reproductions of
drawings, such as made for the black process, and of opaque photo-cliches
in lines, or white and black, than for printing in half tone.

When the material to print upon is thick and wholly impregnated with
diazotized primuline, it is advisable, since the insulation could not be
prolonged to effect the change through, to expose the back of the material
for a certain but short period in order to _clear_ it. This is especially
advantageous when the cliche is not of good intensity.

During the exposure, which varies from 30 seconds to 10 minutes and more
by a dull light, the progresses of the luminous action is seen by the
bleaching of the material which assumes a dingy coloration. But in order
to ascertain when the decomposition is complete on the ground of the
image, it is well to use _tests_ as in the cyanofer process, dipping one
of them in the developer from time to time.

The developers are compounded as follows:

FOR RED.
Beta-naphthol 4 parts
Caustic potassa 6 p