Obsciwatideit: Om: Photosraphie-Processies 75 
or four times in a suitable vessel and dry it by pressing it gently 
between blotting paper. It is then ready for the camera. One 
minute is sufficient for a building on which.a February sun is 
shining, four or five minutes for general views. A rather more 
sensitive paper is prepared by using a mixed solution of five grains 
s iodide of potassium and five grains of chloride of sodium in 
ne ounce of water instead of the iodide of potassium. Five 
poe of bromide of potassium in one ounce of water forms-a 
father less sensitive preparation. ‘These papers may also be made 
more sensitive by washing them again, after the iodide of potas- 
sium, with nitrate of silver, though it will hardly repay the labor. 
The series of salts of silver, according to their sensibility, when 
afterwards brought out by gallic acid, appears to be iodide with 
ehloride, iodide, iodide with bromide, bromide, bromide with 
chloride, chloride, fluoride nitrate ; ferrocyanide, sulphocyanide, 
eyanide.. ‘The series with mercury differs essentially from this. 
_ After exposure these papers are still white, but they need only 
to be fastened as before to another piece of board, and washed 
over once quickly and evenly with a:saturated solution of erys- — 
tallized gallic acid (only three or four grains.in one ounce of wa- 
ter) or with solution of galls, to bring out.in a few moments the 
hidden impression. A weak impression may be brought out by 
several washings, letting the paper dry between each. Too long 
an exposure however in the camera is better than too short.an 
one... When it has come out sufficiently, dip it in water and fix 
it by washing it with the iodide or other solution used in the 
preparation.. Then pecipaas saintnd toed bane: pesca 
paper as before. % 
In views from. whieh: sapien: aati Sivtnlean: cy apiehehie 
over other sensitive paper, it is better perhaps to use the bromide 
throughout, as it leaves the paper whiter and more permeable to 
the chemical rays, or to fix the paper prepared with iodide by 
washing with a bromide solution or hyposulphite of soda. | Care 
must be taken in making a proof not to use the nitrate of silver 
or galls too profusely, otherwise the paper will be stained through. 
Papers merely washed with nitrate of silver, used as soon as dry, 
and brought out afterwards by galls, may answer well for copies. 
These papers should not be exposed to light or heat during apy 
part of the process, and there should be no delay between the use 
of the nitrate ot silves and iodide of potassium ; for the nitrate 
ae 
