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cc, silver and nitrate

ARGENTIC SALTS.—Silver salts, such as argentic chloride, argentic nitrate, etc. See Silver Chloride, Silver Nitrate.

ARCENTOMETER.—An instrument for measuring the quantity of silver nitrate contained in an aqueous solution by its specific gravity. It consists of a simple hydrometer marked with a scale showing the number of grains of silver nitrate per ounce of solution. It is understood, of course, that the latter be perfectly pure and free from other substances. See Silver Nitrate.

ARGENTOTYPE.—Dr. Mailman devised a process to which has been given this name. The following is a description of it t : The following solutions are first of all prepared : Distilled water ico c.c.

Ferric oxalate 20 grammes.

Distilled water ioo c.c.

Silver nitrate 16 grammes.

For use, the proportions are : Solution A 8 c.c.

Solution B 2 c.c.

Suitable paper is coated with this mixture by artificial light, and the paper is rapidly dried by heat, in order that the solution may not sink too deeply into the surface. Either starch or dextrine may be added to the mixture. Exposed under a negative in the usual way, a reddish image on a yellow ground is obtained. Here is the developer recommended :

Distilled water 1,000 c.c.

Potassic oxalate 16o grammes.

The oxalate should be feebly acidified with oxalic acid solution.

Distilled water loo c.c.

Potassium bichromate 4 grammes.

C.—Concentrated nitric acid.

For use take : A zoo c.c.

B 12 drops.

C 4 " The bichromate keeps the whites clear ; for weak negatives, it is desirable to increase the quantity of it ; for strong negatives, to decrease it. Development takes place in the cold. The tones vary a great deal • usually subsequent gold toning is necessary. After development the prints are passed through two or three changes of water acidified with nitric acid. A combined toning and fixing bath is recommended. Under-exposed prints may be intensified by means of a mixture of acetic acid, pyro and nitrate of silver; over-exposure is remedied by prolonged immersion in the wash water acidified with nitric acid.

The name has also been given to an English bromide paper sold ready prepared for enlarging or contact printing. See Bromide Paper.