Hyposulphites, Cyanides, and all fixing agents decompose Nitrate of Silver.
Organic matters, generally, reduce Nitrate of Silver, either with or without the aid of light. Grape Sugar, Albumen, Serum of Milk containing caseine, etc., blacken the Bath, even in the dark. Alcohol and Ether act more slowly, and produce no injurious effect unless the liquid is constantly exposed to light.
These facts indicate that the Nitrate Bath containing volatile organic matters must be preserved in a dark place; also that it should be kept exclusively for sensitizing the Collodion plates, and not used in floating papers intended for the printing process.
Changes in the Nitrate Bath by use.—The solution of Nitrate of Silver employed in exciting the Collodion film gradually decreases in strength, but not so quickly as the Bath used in sensitizing papers for printing. If the amount of Nitrate be allowed to fall as low as twenty grains to the ounce of water, the decomposition will be imperfect, and the film will be pale and blue, even with a highly iodized Collodion.
A gradual accumulation of Ether and Alcohol also takes place in the Bath after long use, in consequence of which the developing solutions flow less readily upon the Collodionized plates, and oily stains are apt to be produced.
Diminished sensitiveness of the Iodide film is sometimes traced to impurities in the Bath, when it is very old, and has been much used. These are probably of an organic nature and may often be partially removed by agitation with kaolin, or animal charcoal. The latter however is objectionable, being usually contaminated with Carbonate of Lime, which makes the Bath alkaline; or (in the case of purified animal charcoal) with traces of Hydrochloric Acid, which liberate Nitric Acid in the Bath. Even the kaolin may as a preliminary precaution be washed with dilute Acetic Acid to remove Carbonate of Lime if any should be present.
SECTION III.
The Conditions which affect the Formation and Development of the Latent Image in the Collodion process.
It will be necessary to preface the observations contained in this Section by defining two terms which are frequently confounded with each other, but are in reality of distinct meaning. These terms are "Sensitiveness" and "Intensity."