146 Dr Fyfe on Photography. 



about eight of water, and the nitrate of silver dissolved in 

 about six of water. The paper is first soaked in the phos- 

 phate, and then dried, after which the nitrate is put on on 

 one side by a brush, the paper 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 yel- 

 low tinge, which becomes black by exposure to light. It is 

 equally sensitive as the chloride, and, in my opinion, gives a 

 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 purpose the nitrate solution is dropped into that 

 of the phosphate of soda, the yellow precipitate is allowed to 

 fall to the bottom, and the supernatant fluid is poured off; 

 what remains must be kept in stone bottles or in a dark place, 

 as it is extremely 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 method has the advantage of being 

 much cheaper than those previously recommended. I some- 

 times add a little mucilage to the fluid, which keeps the phos- 

 phate suspended in it. There are other methods of preparing 

 the paper, which though they do not give it so sensitive, yet 

 are cheaper than those stated ; I allude to the use of the 

 phosphate in solution in ammonia, or, which is cheaper, in 

 the carbonate of ammonia, which is procured by adding con- 

 centrated solution of carbonate of ammonia to the phosphate 

 collected by precipitation as already described, A still cheaper 

 fluid may be prepared by adding a strong solution of nitrate 

 of silver to a concentrated solution of carbonate of ammonia, 

 by which a carbonate of silver is obtained in solution, and which 

 can be applied to the paper on one side by means of a brush. 

 Paper thus prepared is white ; it has the advantage of being 

 easily prepared, and of giving, on exposm-e to light, a uniform 

 ground which is of a brownish colour.* 



• Instead of purchasing lunar caustic of commerce, a cheaper method of 

 ocuring it is to dissolve pure silver iu nitric acid diluted with its own 



