Calcium Sulphate

CaSO4 + 2H2O. Plaster of Paris; Gypsum.

Fine, white powder. Soluble, with difficulty, in water. If mixed with a small quantity of water, so as to form a paste, it will gradually thicken afterwards, solidifying to a hard mass of hydrated sulphate. Should be kept in air-tight glass-stoppered bottles. Useful for mending leaks or repairing broken bottles. If stale, heat to 4000 Fahr., before using.

Calcium Tube

A cylindrical tube of metal used for the preserving of platinum or other ready sensitized papers. (See Calcium Chloride.)



The first paper negative process, invented by Henry Fox Talbot, and very largely used at one time.


A photograph, the surface of which is slightly convex. Made in this shape, after mounting, by means of a die and press.


Essentially a light-tight box with a lens at one end and a means for supporting a sensitive plate or film at the opposite end at right angles to the axis of the lens. Various modifications have been made to this simple form of construction for various purposes.

Box Camera

The simplest form of construction of the camera. Usually fitted with single lenses and shutters, giving both instantaneous and time exposures.

Detective Camera

A camera made to look as little like a camera as possible, or one which is capable of being used to take pictures when hidden from sight.

Double Extension or Long Focus Camera

Enlarging and Copying Camera

A camera with extension bellows for copying and enlarging negatives or positives on glass or paper.

Ferrotype Camera

An instrument usually employed in making ferrotypes. Contains a number of small lenses, each being partitioned off. It is thus possible to make several images upon the plate at one time.

Film Camera

Film cameras are of two general forms, one being of the box type, the other the folding type of construction. In both roll films are used in place of dry plates.

Film-Plate Camera

This is a form of camera in which either cut films or plates may be used. The films are arranged in what is known as a film pack, and this latter is inserted in the film pack adapter, which takes the place of the regular plate-holder. Camera, Fixed Focus - I, 69, 70.

A camera in which the lens cannot be moved for adjustment. The lens is focused for practically any distance within certain limits. (See Lens, Fixed Focus.)

Folding Camera

One of the most compact forms of construction for cameras. When closed the bed of the instrument forms one side and the bellows being operated on a track is brought together inside of the box, thus reducing the bulk.

Hand Camera

A convenient form of camera which can be operated when held in the hand. Usually the front portion holding the lens slides into the box, which latter is then closed by raising the bed.