SCIENTIFIC SUMMARY. 
335 
filtering paper is free from tlie hyposulphite. The only kind of filtering paper 
to he depended upon is the Swedish. 
A simple Dry Plate Process . — M. Romain Talbot, at a meeting of the 
French Photographic Society, exhibited negatives on plates preserved six 
months before exposure, and which were said to have been prepared in the 
following extremely simple way. M. Talbot used Harnecker's collodion, 
sensitised in a bath containing about 50 grns. of silver to the ounce, and one 
drdp of pure nitric acid. After sensitising, the plate is drained and washed, 
first in distilled, then in ordinary water, and then in distilled water again. 
After being dried at a temperature of about 90^ Fahr. it is ready for use. 
The exposure required is about three times as long as a wet plate would 
receive under the same circumstances of subjects and light. To develop the 
plate is kept in a bath of distilled water about ten minutes, is then placed 
on the dipper of the silver bath and given four or five dips, and then sub- 
jected to the action of the following developer — sulphate of iron, 75 grammes; 
water, 1,800 gTammes ; glacial acetic acid, 45 grammes; absolute alcohol, 
60 grammes. When the image is well out, wash thoroughly, and strengthen 
with a solution composed of pyrogallic acid, 1 gramme; distilled water, 
225 grammes ; glacial acetic acid, 10 grammes ; to which is added nitrate of 
silver 1 gramme ; distilled water, 48 grammes ; glacial acetic acid, 1 gramme. 
Fix with hyposulphite of soda 1 gramme ; water, 3 grammes ; and to pre- 
serve the negative, coat it with gum. 
Vitrified Caoutchouc . — This has been introduced in Paris as a substitute 
for glass in photography, the clearness, evenness, and transparency of which 
it possesses without its thickness, weight, or brittleness. It is to be used for 
various purposes, such as the transferring of collodion films, for excluding 
air or moisture from valuable silver prints, and for use in the carbon process. 
The films are as strong and flexible as paper, and can be manufactured in 
sheets of any required size. 
A New Actinometer . — Dr. Vogel has introduced a new actinometer, 
which is so arranged as to expose sensitive paper to light under a ladder, 
formed by layers of paper resisting in varying and regular degrees, each one 
being indicated by its particular number, the action of the light. The 
instrument is used in a kind of frame or box, resembling an ordinary printing 
frame, bnt opening at the side. 
Mounts for Photographs. — MM. Fordes and Davanne warn their photo- 
graphic brethren against the use of mounts with gilt borders. These borders 
are made with bronze powders, which are mostly composed of bisulphide of 
tin, and may, from the mode in which it is manufactured, contain traces of 
free sulphur, the most minute trace of which, in the pores of the paper, 
would exercise an injurious effect upon any photograph it came in contact 
with. If particles of bronze powder be scattered on a photograph and their 
action under the influence of moisture be observed, the effect will soon be- 
come visible, in the shape of black spots surrounded by rings of yellowish 
white. 
A Supposed Wonderful Discovery. — A photographer residing in Man- 
chester, Mr. McLachlan, some few months since addressed letters to the 
Photographic Journals, in each of which he claimed to have made some 
wonderful discoveries, which would render the photographic process, hence- 
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