results are also obtained with well sized
papers.

The sensitizing should be done by a very diffused daylight, and the
drying, of course, in a dark room. When sensitized the paper is yellowish
green. It should be well dried for keeping, and rolled or wrapped in
orange or brown paper and preserved from the action of dampness and of the
air. It does not keep well, however, no more than two or three months,
perhaps, in good condition; but the sooner it is employed the finer the
proofs, the better the whites and more rapidly is the paper impressed.

There is in the market a paper which keeps for a long time. It is
prepared by adding a small quantity of gum arabic or of dextrine to the
sensitizing solution. Good for the reproduction of line work, it does not
give very satisfactory results for pictures in half tones.

The following compound gives a paper much more sensitive, but not keeping
so long, than that prepared according to the formula previously given:

Tartaric acid 25 parts
Ferric chloride, solution 80 parts (in volume)
at 45 deg. Baume
Water 100 parts

When the acid is dissolved, add gradually concentrated aqueous ammonia,
just enough to neutralize the solution--170 volumes, about. The chemical
change consists in the formation of ferric tartrate. Let cool the
solution, then, after adding the following, keep it in the dark:

Potassium ferricyanate 211/2 parts
Water 100 parts

Another and very sensitive preparation is the following:

A. Iron perchloride, 40 parts
cryst
Oxalic acid 10 parts
Water 100 parts
B. Potassium 20 parts
ferricyanate
Water 100 parts
Mix

_Printing._--The process we describe yields negative impressions, that is a
positive image from a negative cliche, and a negative image from a
positive cliche, exactly as the silver printing-out process ordinarily
employed in photography. Consequently, for the production of non-reversed
proofs from plans, etc., the original drawing should be placed _face
downwards_ on the glass plate of the printing frame, and, upon the back,
the sensitive paper is laid and pressed into perfect contact by means of a
pad, felt or thick cloth.

The printing frame is that used by photographers. The lid is divided,
according to the side, in two, three and even four sections, held by
hinges and fastened for printing b