minute fragments of glass are liable to settle
upon the sensitive film and to cause spots and scratches during the
packing operations; any defect of this kind renders a plate worthless
to the photographer. When any breakages take place in the cutting, it
is best that they should occur at the outset, and not after the plate
has been coated with emulsion. The cutting when necessary is effected
by the aid of a "cutting board," Fig. 2, invented by Mr. Cowan, and
now largely in use in the photographic world. This appliance is used
to divide into two equal parts, with absolute exactness, any plate
within its capacity, and it is especially useful in dimly lighted
rooms. It consists of four rods pivoted together at the corners and
swinging on two centers, so that in the first position it is truly
square, and in other positions of rhomboid form, the two outer bars
approaching each other like those of a parallel ruler. The hinge flap
comes down on the exact center of the plate, minus the thickness of
the block holding the diamond. By this appliance plates can be cut in
either direction. Fig. 3 represents a similar arrangement for cutting
a number of very small plates out of one large one; in this the hinge
flap is made in the form of a gridiron, and the bars are spaced at
accurate distances, according to the size of the plate to be cut, so
that a plate 10 in. square, receiving four cuts in each direction,
will be divided into twenty-five small plates.

[Illustration: Fig. 5.]

Before being cleaned all sharp edges are roughly taken off those
plates intended for machine coating by girls, who rub the edges and
corners of the plates upon a stone; the plates are then cleaned by any
suitable method in use among photographers. The plates, now ready for
the coating room, have to be warmed to the temperature of the
emulsion, say from 80 deg. F. to 100 deg. F., before they pass to the
coating machine, the inventor of which, Mr. Cadett, having come to the
conclusion that, if the plates are not of the proper temperature, the
coating given will be uneven over various parts of the surface. The
plate-warming machine is represented in Fig. 4; it was designed by Mr.
A. Cowan, and made by his son, Mr. A. R. Cowan. It consists of a
trough 7 ft. long by 3 in. deep, forming a flat tank, through which
hot water passes by means of the circulating system shown in the
engraving. To facilitate the traveling of the glass plates without
friction the top