176 Miscellanies. 
solution of sea-salt, and when dry, to rub it over on one side with so- 
lution of Junar caustic, by which chloride of silver is formed, and 
adheres to the paper. As thus prepared, it acquires a dark color on 
exposure to light; the depth of color depending on the strength of the 
solutions ; hence it may vary from lilac to deep purple, approaching 
to black. 
In preparing paper by this method, it is very difficult to get the chlo- 
ride uniformly spread over the surface, and accordingly, when exposed 
to light, it often gives a variety of shades; indeed, in many places it 
continues white. It was this that induced me to try the use of other 
salts of silver; and the one which I have found to answer best is the 
phosphate, procured in the usual way, by the addition of the phosphate 
of soda to the solution of lunar caustic. In preparing the paper by 
this method, I generally employ one part of phosphate of soda dissol- 
ved in about eight of water, and the nitrate of silver dissolved in about 
six of water. The paper is first soaked in the phosphate, and then 
dried, after which the nitrate is put on on one side by a brush, the pa 
per again dried and afterwards again put through the salt, by which 
any excess of silver is converted to phosphate. As thus prepared, 
it acquires a yellow tinge, which becomes black by exposure to light 
It is equally sensitive as the chloride, and, in my opinion, gives 4 
much more pleasing variety of shades. 
Instead of preparing the paper by the process described, I frequently 
employ the phosphate precipitated before applying it, for which pur 
pose the nitrate solution is dropped into that of the phosphate of soda, 
the yellow precipitate is allowed to fall to the bottom, and the supe! 
natant fluid is poured off; what remains must be kept in stone bottles 
or in a dark place, as it isextremely sensitive to light. In preparing 
the paper with it, it is put on with a broad flat brush, and then dried in 
the usual way. Though there is a little difficulty at first in getting the 
phosphate uniformly spread over the surface, yet by a little practice 
a uniform ground is easily given, and when once acquired, the metho 
has the advantage of being much cheaper than those previously sieth 
commended. I sometimes add a little mucilage to the fluid, whi 
keeps the phosphate suspended in it. There are other methods 0 
preparing the paper, which though they do not give it so sensitives ye 
are cheaper than those stated; I allude to the use of the phosphate " 
solution in ammonia, or, which is cheaper, in the carbonate of ammo- 
nia which is procured by adding concentrated solution of carbonate of 
ammonia to the phosphate collected by precipitation as already de 
scribed. A still cheaper fluid may be prepared by adding a strong Lat 
lution of nitrate of silver to’a concentrated solution of carbonate of 
ammonia, by which a carbonate of silver is obtained in solution 
