and it is ready for receiving
the image. When the impression has been received, which will require
from one to five minutes according to the state of the weather, it must
be washed with a saturated solution of gallic acid to which a few drops
of the aceto-nitrate of silver, made as above, have been added. The
image will thus be gradually brought out, and may be fixed with
hyposulphite of soda. To obtain the positive picture, paper must be
used brushed over with an ammonio-nitrate of silver, made thus: forty
grains of nitrate of silver is to be dissolved in one ounce of
distilled water, and liquid ammonia cautiously added till it
re-dissolves the precipitate.

A pleasing effect may be given to calotype, or indeed to all
photographic pictures, by waxing them at the back, and mounting them on
white paper, or if colored paper be used, various beautiful tones of
color are produced.

POSITIVE CALOTYPE.

At a meeting of the British Association, Professor Grove described a
process by which positive calotype pictures could be directly obtained;
and thus the necessity to transfer by which the imperfections of the
paper are shown, and which is moreover a troublesome and tedious
process, is avoided. As light favors most chemical actions, Mr. Grove
was led to believe that a paper darkened by the sun (which darkening is
supposed to result from the precipitation of silver) might be bleached
by using a solvent which would not attack the silver in the dark, but
would do so in the light. The plan found to be the most successful is
as follows: ordinary calotype paper is darkened till it assumes a deep
brown color, almost amounting to black; it is then redipped into the
ordinary solution of iodide of potassium, and dried. When required for
use it is drawn over dilute nitric acid--one part acid to two and a
half parts water. In this state, those parts exposed to the light are
rapidly bleached, while the parts not exposed remain unchanged. It is
fixed by washing in water, and subsequently in hyposulphite of soda, or
bromide of potassium.

Mr. Grove also describes a process for converting a negative calotype
into a positive one, which promises, when carried out, to be of great
utility.

Let an ordinary calotype image or portrait be taken in the camera, and
developed by gallic acid; then drawn over iodide of potassium and
dilute nitric acid and exposed to full sunshine; while bleaching the
dark parts, the light is redarkening th