Slaty Blue.

1.—­One part of the above solution
to three parts of a solution of citrate of ammonia.

Greenish Brown.
2.—­Citric acid.               180 grains
Carbonate of ammonia.       50   "

3.—­Citrate of ammonia.        250 grains. 
Chloride of sodium.          2   "

4.—­Citrate of ammonia.        250 grains. 
Chloride of sodium.          4   "

Sepia Brown.
5.—­Citrate of ammonia.        250 grains. 
Chloride of sodium.          8   "

Clear Red Brown.
6.—­Citric acid.               120 grains. 
Carbonate of magnesia.      76   "

Warm Gray Brown.
7.—­Citric acid.               120 grains. 
Carbonate of soda.         205   "

Deep Red Brown.
8.—­Citric acid.               120 grains. 
Carbonate of potash.       117   "

Green Blue.
9.—­Citric acid.                90 grains. 
Carbonate of soda.         154   "
Citrate of potash.          24   "
Oxalate of potash.           6   "

Sepia Red.
10.—­Citric acid.                80 grains. 
Carbonate of soda.         135   "
Citrate of potash.          12   "
Oxalate of potash.           3   "

11.—­Citric acid.               108 grains. 
Carbonate of magnesia.      68   "
Carbonate of potash.        12   "
Oxalate of potash.           3   "

Sepia Yellow.
12.—­Citric acid.                40 grains. 
Carbonate of magnesia.      25   "
Citrate of ammonia.        166   "

13.—­Citric acid.               120 grains. 
Carbonate of magnesia.      72   "
Carbonate of ammonia.       72   "
Chloride of sodium.          8   "

Blue Black.
14.—­Citric acid.               120 grains. 
Carbonate of ammonia.       70   "
Carbonate of magnesia.      15   "

15.—­Citric acid.               120 grains. 
Carbonate of magnesia.      38   "
Carbonate of ammonia.       44   "

16.—­Citric acid.                90 grains. 
Carbonate of magnesia.      57   "
Citrate of potash.          54   "
Oxlate of potash.           18   "

17.—­Citric acid.                72 grains. 
Carbonate of magnesia.      45   "
Citrate of potash.          54   "
Oxalate of potash.          18   "

18.—­Citric acid.                60 grains. 
Carbonate of magnesia.      38   "
Citrate of potash.          68   "
Oxalate of potash.          22   "

A more Intense Blue Black.
19.—­Citric acid.                30 grains. 
Carbonate of magnesia.      18   "
Citrate of potash.         100   "
Oxalate of potash.          33   "

A Clearer Blue.
20.—­Citrate of potash.         136 grains. 
Oxalate of potash.          44   "

In the photographic exhibition at Florence, the firm of Corvan[1] places on view a frame containing twenty proofs produced by the foregoing twenty formulae, in such a way that the observer can compare the value of each tone and select that which pleases him best.—­Le Moniteur de la Photographie, translated by British Jour. of Photo.