Quantitative Analysis

The chemical examination of bodies with a view to ascertain in what proportions certain substances are contained in other substances.

Quart

One-fourth of a gallon. Quarter-Plate.

An English size of plate, being 3 1/4 x 4 1/4 inches.

Quinol

(See Hydroquinon.)

Rack and Pinion

An adjustment on cameras to facilitate varying the distance between the lens and the ground-glass or sensitive plate. It usually consists of a toothed or geared wheel which is caused to rotate on a straight toothed track. The Rack and Pinion is also employed on various scientific instruments where accurate adjustment is required.

Drying Rack

(a) A wood or metal frame on which to set plates for drying. The most common are those which fold up when not in use.

(b) A frame on which cloth is stretched. Used for drying prints.

Radiography

(See X-Ray Photography.)

Rapidity

(a) When used with reference to a lens the term rapidity means the relation of the length of focus to the working aperture. The larger the aperture as compared to the focal length the more rapid is the lens, (b) When spoken of plates or papers rapidity means the sensitiveness of the plates or papers to actinic light. The degree is registered by a sensitometer.

(c) Rapidity is also a term used when speaking of the speed of a shutter.

Rapid Lens

(See Lens, Rapid.)

Rapid Rectilinear Lens

(See Lens, Rapid Rectilinear.)

Rapid Symmetrical Lens

(See Lens, Rapid Symmetrical.) Ray.

A line of light proceeding from a point of radiation or reflection. A collection of parallel rays constitutes a BEAM; a collection of diverging or converging rays, a PENCIL. The component elements of light also have the term ray applied to them. Ex. The yellow rays of the spectrum.

Ray Filter

(See Color Filter.)

Principal Rays

A term applied to those rays which pass perpendicularly from the observer's eye to the perspective picture.

Ultra-Red Rays

The rays at the extreme red end of the spectrum. They are practically invisible and give the greatest amount of heat. (See Prismatic Colors.)

Ultra-Violet Rays

The rays at the extreme violet end of the spectrum. They vibrate so rapidly that they are invisible. They possess the greatest chemical activities of any rays. (See Prismatic Colors.)

Visual Rays

A term applied to the line of light imagined to come from the object to the eye.

Reaction

A chemical term applied to the result of bringing two or more elements or compounds together, one or more new bodies being formed.

Ready-Sensitized Paper

A term applied to commercially sensitized printing-out papers.

Reagent

A chemical term applied to a substance used to effect chemical change in another substance, in order to identify its component parts or ascertain its composition.