Alum

A12K2(SO4)4 + 24H2O - I, 205; II, 288, Page 139; IV.

Potash Alum, or Aluminum and Potassium Sulphate

Large, colorless crystals or very fine, white powder. Astringent taste, acid reaction. Soluble in glycerin, 9 parts water, 0.3 parts boiling water. Insoluble in alcohol. Used in solutions for hardening gelatin films and preventing frilling; also for clearing and removing stains.

Chrome Alum

Cr2K2(SO4)4 + 24H2O - V. Chromium and Potassium Sulphate. Dark violet-red, regular crystals; ruby-red by transmitted light.

Soluble in water. Stronger in action than ordinary, or potash, alum. Useful for most all the purposes of ordinary alum.

Aluminum

Al.

Tin-white, malleable, ductile metal capable of taking brilliant polish. One of the lightest of the metals. Soluble in mineral acids and strong alkaline solutions. Used for camera fittings and lens mounts; also in powdered form in the composition of some flashlight mixtures.

Black Varnish for Aluminum

(See Varnish.) Aluminum Chloride

A12C16 + 12H2O.

Yellowish-white, granular, crystalline powder. Soluble in water, alcohol and ether. Used sometimes for toning gela-tino-chloride prints; also employed in some of the modern color photography processes.

To Clean Aluminum

Polished parts can be cleaned best with black " bottled " India rubber, not vulcanized. When possible, however, wash in:

Caustic Soda.....................................................

1 dr.

Water ................................

10 ozs.

Then rinse in clean water and dry quickly. The best way to dry is to shake the aluminum in a box of hot, dry, hardwood sawdust.

Amateur

(See Photographer, Amateur.)

Amber

A mineralized pale-yellow, sometimes reddish or brownish, resin of extinct pine trees, found in greatest abundance on the shores of the Baltic, where it is thrown up by the sea. It is a hard, translucent, brittle substance. Soluble in benzole or chloroform. Used in making various varnishes.

Ambrotype

A wet collodion positive backed with black varnish. (See Ferrotype.)

Amidol

C6H8N2O + 2HC1 - II, 460, Page 364; IV, 1034; V, 671, 672; VIII.

Diamidophenol Hydrochloride; or Diamidophenol

Grayish-white crystals. Soluble in water; slightly soluble in alcohol. Used as a developing agent, and is especially valuable as a bromide paper developer.

Amidophenol

C6H7NO. Para-amidophenol. Crystalline powder. Soluble in water and alcohol; darkens on exposure to light. Used as a developing agent.

Ammonia

NH3.

Aqua Ammonia, Liquor Ammonia, Spirits of Hartshorn or Spirits of Ammonia. Colorless, inflammable liquid; stringent, suffocating, odor of ammonia. Used as an alkali or accelerator with pyro. May be used for fixing prints. Employed in some dry-plate emulsions. (See Ammonia Water.)