--184 deg. Fahr.),(23) in an agate glazed iron tray placed upon a water
bath at the above temperature. By simply drawing the proof over it, the
image is at once developed.(24)

When the proof is thought to be over-exposed, the oxalate solution can be
employed at a lower temperature. If, on the contrary, it is
under-exposed, the solution may be heated even to the boiling point.

The developer can be used over and over again. _It should always have an
acid reaction._

According to Mr. Borlinetto a sepia tone is obtained by using the
following cold developer:

Saturated solution of 120 parts
potassium oxalate
Saturated solution of 13 parts
copper chloride
Oxalic acid 1.5 part

After developing the proofs are _immediately_ immersed for fixing in a
solution of hydrochloric acid, 1 to 80 of water, renewed so long as the
paper is tinged yellow (about three times), leaving the proofs ten minutes
in each solution. Lastly, they are washed to remove the acid.

The platinotype has been still improved by Captain Pizzighelli, who
devised the following methods of operating by which the impressions are
obtained by the continuous action of light, that is, without development,
thus rendering the platinotype just as simple as the ordinary printing-out
silver process.

In these new processes to the sensitizing solution is added the alkaline
oxalate, which effects the reduction of the platinous salt during the
exposure to light. Consequently the prepared paper is insolated until the
image appears as it should be, or--which is exceedingly useful in cloudy
weather--until it is entirely visible but still deficient in delicate half
tones, for in the dark the action proceeds and the image developing itself
will be found finished in a period which may extend to a few hours. But
it can be, however, developed in a few seconds by immersion in a cold or
slightly warm solution of sodium carbonate, 1:25 of water. The image is
fixed as directed in the foregoing process.

The paper, prepared exactly as in the former process and kept in the
calcium box until wanted for use, should not be employed quite dry, but
allowed to absorb a little moisture by hanging it in the dark room.
Hence, the India rubber and other protecting pads can be dispensed with.
They are even objectionable, for dampness is absolutely necessary to
promote the chemical changes by which the image is developed.

A. AMMONIO-FERRIC OXALATE SOLUTION