Achromatic Lens

(See Lens, Achromatic.)

Acid

A sour substance. Chemically, it is a compound containing one or more atoms of hydrogen. Turns blue vegetable colors to red. Just the opposite in action to alkalies. Acids used in photography are treated under their respective headings, as follows:

Acid Acetic

C2H4O2 - IV, 701.

Strongly acid liquid; sharp acetic odor. Should be kept in a stoppered bottle. Sold in various strengths, the strongest being known as glacial acetic acid. Used to acidify developer in wet plate process; in silver intensification to delay deposit of silver; in uranium toning to prevent any trace of alkalinity; etc.

Commercial Acid Acetic

No. 8 - 25%.

A diluted form of acetic acid (therefore of weaker strength). This strength of acetic acid is in most common use in photography, and having a strength of 25% it contains one part of glacial acetic acid to four parts of water.

Glacial Acid Acetic

99 1/2%.

Term applied to the pure acetic acid.

Acid Boric

H3BO3.

Colorless crystals; pearly luster; slightly unctuous to touch; odorless; faint, bitterish-acid taste. Soluble in 18 parts water, 15.3 parts alcohol, 3 parts boiling water, and 4.3 parts boiling alcohol.

Acid Carbolic

C6H6O.

Colorless crystals; characteristic odor; when highly diluted has sweetish taste. Deliquescent in moist air. Soluble in alcohol, ether, chloroform and glycerine; in about 20 parts water; in 2 parts olive oil. Used principally for disinfecting solutions or mixtures. Keep in dark amber, well-stoppered bottles.

Acid Carbonic

CO2 - IV, 249. Carbon Dioxide. Highly volatile, colorless liquid. Soluble in cold water. Is used but little in photography, the photographer coming in contact with it mostly in water. A test for its presence in water is given in the above reference.

Acid Chromic

CrO3.

Chromium Trioxide. Reddish-brown, needle-shaped crystals. Keeps well in glass stoppered bottle. Soluble in water. Used sometimes in place of potassium bichloride.

Acid Citric

C6H8O7 + H2O - IV, 153, 154.

Colorless, rhombic crystals, or white powder; odorless; very acid; permanent in dry air at ordinary temperature. Efflorescent in warm air, deliquescent in moist air. Soluble in water, alcohol and ether. The crystalline form of this chemical is preferable for photographic work. Used as a preservative in solutions of pyro, also to acidify wet plate developer and silver intensifier. Employed in alum clearing solution and in solution "F" in the autochrome process.

Acid Fixing Bath

A normal hypo bath to which has been added an acid and other chemicals to prevent formation of developer stain; also to act as a hardening solution. The index for Volume II refers to various formulae.

Acid Gallic

C7H6O6 + H2O.

Colorless or slightly yellowish, silky, interlaced needles; odorless; astringent, slightly acidulous taste. Permanent in air. Soluble in 5 parts alcohol, 40 parts ether, 12 parts glycerin, and about 100 parts water. Used in various early processes as a developer, especially for paper negatives and also in the callotype process.