ced.

2. Potassium 10 parts
bichromate
Manganous sulphate 4 parts
Potassium 20 parts
bisulphate
Water 300 parts
3. Ammonium 5 parts
bichromate
Ammonium chloride 5 parts
Cupric sulphate 1 part
Sulphuric acid 8 parts
Water 150 parts

Good well-sized paper should be employed. Rives is too tender and absorbs
too much. Steinbach is better. For small sizes, whatever be the paper
selected, it is well to size it with starch and, if possible, to calender
it on a hot steel plate, or, in lieu, to iron it. This is not, however, a
sine qua non. The paper is sensitized by brushing or by floating. To
sensitize by floating, it should be left but for a few seconds on the
solution and removed by dragging it on a glass rod in order to remove the
superfluous liquid. Only the surface of the paper should be impregnated,
otherwise the whites would be more or less tinted and the image imbedded
not as sharp.

Sensitized, the paper must be dried as rapidly as possible. It does not
keep, and should be employed the day it is prepared or the day after,
keeping it well wrapped in paper.

As said above, it is exposed under a positive cliche, plans, designs,
etc., drawn on tracing paper or linen. The more transparent the material,
the more rapid the chemical changes. During the insolation--and it is very
short--the chromic compound is reduced, the parts corresponding to the
ground, that is, the transparent parts of the cliche, are discolored,
while those under the design remain unaltered; the image being, therefore,
faintly visible, and being formed of the chromic mixture, it is developed
by the fumes of aniline in a blue black tone. Therefore, if the paper be
not sufficiently exposed, the ground is colored like the image, although
not as deeply, since the dye formed is proportionate to the more or less
quantity of unreduced compound, and if exposed too long the image is
imperfectly developed or not at all by excess.

The discoloration of the ground, which turns to a greenish hue, easily
indicates when the exposure is sufficient. But, to ascertain it, the
beginner should use _tests_ as in the cyanofer process. Mr. Endemann
regulates the time of exposure by partly covering a strip of the sensitive
paper with a piece of the tracing material upon which the design is made,
and exposing the whole until t