Orthostigmatic Lens

(See Lens, Orthostigmatic.)

Ortol

C6H4 (OH) NHCH3HCl - II; IV. Methylorthoamidolphenol. A yellowish-white crystalline substance soluble in water; resembles pyro in action, but more cleanly to use; closely allied to rodinol; may be used, instead of mercury, for intensification.

Ounce

An English unit of weight.

Oval

Having the shape of, or resembling, the longitudinal section of an egg; i. e., eliptical.

Over-Development

(See Developing, Over.)

Over-Exposure

(See Exposure, Over.)

Oxalate Developer

A developer composed of potassium oxalate; used for developing platinum prints.

Oxalate of Ammonium

(See Ammonium Oxalate.)

Oxalate of Iron

(See Ferrous Oxalate.)

Oxalate of Potash

(See Potassium Oxalate.)

Tests for Oxalates

Solutions containing oxalate will, with the addition of barium nitrate, give a white precipitate soluble in hydrochloric acid. The addition of silver nitrate to oxalate solutions will give a white precipitate soluble in nitric acid.

Oxalic Acid

(See Acid, Oxalic.)

Ox-Gall

Yellowish-green, thick extract; unpleasant odor; disagreeable, bitter taste. The bitter fluid secreted by the liver of the ox.

When clarified by boiling with animal charcoal and filtering it is used for water color paintings, etc. Also used to overcome the resistance of a greasy surface.

Oxygen

O.

A gaseous element; forms 8-9 by weight of water; is present and absolutely necessary in the air we breathe; is a component part of various chemicals; is necessary for the reduction of the photographic silver image, for the more rapidly the developer absorbs oxygen the greater will be the reducing action on the latent silver image, which image is changed to metallic silver.

Oxy-Hydrogen

A mixture or combination of oxygen and hydrogen. Used as an illuminant in optical lanterns.

Ozobrome

A simplification or modification of the carbon process permitting the making of carbon prints without the direct action of light. Also the making of carbon enlargements from bromide enlargements, thus doing away with the trouble and expense of making enlarged negatives.

Ozotype

A modern process which is a modification of the carbon process; does away with the necessity of transferring the pigment and shows a visible image during printing.

Pad

Usually a piece of felt or similar material used to place between the back of the printing-frame and the sensitive paper lying on the negative, to insure uniform contact between the printing paper and the film of the negative. Used in platinum printing to absorb dampness, as well as assist in keeping the paper in perfect contact with the negative.

Panchromatic Plates

(See Plates, Panchromatic.)