Quite recently Messrs. Marion & Company, London, began on their own
account to manufacture sensitive photographic plates by machinery, and
the operations are exceedingly delicate, for a single minute air
bubble or speck of dust on a plate may mar the perfection of a
picture. Their works for the purpose at Southgate were erected in the
summer of 1886, and were designed throughout by Mr. Alexander Cowan.
[Illustration: Fig. 1.]
Buildings of this kind have to be specially constructed, because some
of the operations have to be carried on in the absence of daylight,
and in that kind of non-actinic illumination which does not act upon
the particular description of sensitive photographic compound
manipulated. Glass and other materials have therefore to pass from
light to dark rooms through double doors or double sliding cupboards
made for the purpose, and the workshops have to be so placed in
relation to each other that the amount of lifting and the distance of
carriage of material shall be reduced to a minimum. Moreover, the
final drying of sensitive photographic plates takes place in absolute
darkness. Fig. 1 is a ground plan of the chief portion of the works.
In this cut, A is the manager's private office, B the counting house,
C the manager's laboratory, and D his dark room for private
experiment, which can thus be conducted without interfering with the
regular work of the establishment. E is the carpenter's shop and
packing room, F the albumen preparation room, G the engine room, with
its two doors; the position of the engine is marked at H. The main
building is entered through the door, K; the passage, L, is used for
the storage of glass, and has openings in the wall on one side to
permit the passage of glass into the cleaning room, M; this room is
illuminated by daylight. The plates, after being cleaned, pass into
the coating rooms, N and O, into which daylight is never admitted; the
coating machine is in the room, N, and three hand coating tables in
the room, O; both these rooms are illuminated by non-actinic light.
[Illustration: Fig. 2.]
[Illustration: Fig. 3.]
The walls of N and O are of brick, to keep these interior rooms as
cool as possible in hot weather, for the making of photographic plates
is more difficult in summer time, because the high temperature tends
to prevent the rapid setting of the gelatine emulsion upon them. At
the end of these rooms and communicating with both is the lift, P, by
which the coated plates are carried to the drying rooms above, which
there cover the entire area of the main building; they consist of two
rooms measuring 60 ft. by 30 ft., and are each 30 ft. high at the
highest part in the center of the building; these rooms are
necessarily kept in absolute darkness, except while the plates are
being stored therein or removed therefrom, and on such occasions
non-actinic light is used. After the plates are dry, they come down
the lift, Q, into the cutting and packing room, R, which is
illuminated by non-actinic light. In the drying rooms the batches of
plates are placed one after the other on tram lines at one end of the
room, and are gradually pushed to the other end of the building, so
that the first batches coated are the first to be ready to be taken
off when dry, and to be sent down the lift, Q. The plates in R, when
sufficiently packed to be safe from the action of daylight, are passed
through specially constructed openings into the outside packing room,
S, where they are labeled. The chemicals are kept in the room, U,
where they are weighed and measured ready for the making of the
photographic emulsion in the room, U. The next room, V, is for washing
small experimental batches of emulsion, and W is the large washing
room. The emulsion is then taken into the passage, X, communicating
with the two coating rooms. A centrifugal machine in the room, Y, is
used for extracting silver residues from waste materials, also for
freeing the emulsion from all soluble salts. Washing and cleaning in
general go on in the room, Z.
[Illustration: Fig. 4.]
The glass for machine coating is cut to standard sizes at the
starting, instead of being coated in large sheets and cut afterward--a
practice somewhat common in this industry. The disadvantage of the
ordinary plan is that 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 of the tank is a sheet of plate glass bedded on a
sand bath. An assistant at one end places the glasses one after the
other on the warm glass slab, and by means of a movable slide pushes
them one at a time under the cover, which cover is represented raised
in the engraving to show the interior of the machine. After having put
one glass plate on the slide, another cannot be added until the man in
the dark room at the other end of the slide has taken off the farthest
warmed plate, because the slide has a reciprocating movement. This
heating apparatus is built at right angles to the coating machine in
the next room, in order to be conveniently placed in the present
building; but it is intended in future to use it as a part of the
coating machine itself, and to drive it at the same speed and with the
same gearing, so that the cold plates will be put on by hand at one
end, get warmed as they pass into the dark room, at the other end of
which they will be delivered by the machine in coated condition.
Underneath the heating table is a copper boiler, with its Bunsen's
burner of three concentric rings to get up the temperature quickly and
to give the power of keeping the water under the heating slab at a
definite temperature, as indicated by a thermometer. The cold water
tank of the system is represented against the wall in the cut.
[Illustration: Fig. 6.]
Fig. 5 represents the hot water circulating system outside the coating
rooms for keeping the gelatine emulsions in these dimly lighted
regions at a given temperature, without liberating the products of
combustion where the emulsion is manipulated. The temperature is
regulated automatically. It will be noticed where the pipes enter the
two coating rooms, and Fig. 6 shows the copper inside one of them
heated by the apparatus just described. The emulsion vessel in the
copper is surrounded by warm water, and the copper itself is jacketed
and connected with the hot water pipes, so forming part of the
circulating system.
[Illustration: Fig. 7.]
Fig. 7 is a general view of the coating machine recently invented by
Mr. Cadett, of the Greville Works, Ashtead, Surrey. The plates warmed
in the light room, as already described, are delivered near the end of
the coating table, where they are picked off a gridiron-like platform,
represented on the right hand side of the cut, and are placed by an
assistant one by one upon the parallel gauges shown at the beginning
of the machine proper; they are then carried on endless cords under
the coating trough described farther on. After they have been coated
they are carried onward upon a series of four broad endless bands of
absorbent cotton--Turkish toweling answers well--and this cotton is
kept constantly soaked with cold water, which flows over sheets of
accurately leveled plate glass below and in contact with the toweling;
the backs of the plates being thus kept in contact with fresh cold
water, the emulsion upon them is soon cooled down and is firmly set by
the time the plates have reached the end of the series of four wet
tables. They are then received upon one over which dry toweling
travels, which absorbs most of the moisture which may be clinging to
the backs of the plates; very little wet comes off the backs, so that
during a day's work it is not necessary to adopt special means to
redry this last endless band. What are technically known as "whole
plates," which are 8½ in. by 6½ in., are placed touching each other
end to end as they enter the machine, and they travel through it at
the rate of 720 per hour; smaller sizes are coated in proportion, the
smaller the plates the larger is the number coated in a given time.
The smaller plates pass through the machine in two parallel rows,
instead of in a single row, so that quarter plates, 4¼ in. by 3¼ in.,
are delivered at the end of the machine at the rate of 2,800 per hour,
keeping two attendants well employed in picking them up and placing
them in racks as quickly as they can do the work. The double row of
cords for carrying two lines of small plates through the machine is
represented in the engraving. Although the plates touch each other at
their edges on entering the machine, they are separated from each
other by short intervals after being coated; this is effected by
differential gearing. The water flowing over the tables for cooling
the plates is caught in receptacles below and carried away by pipes.
Between each of the tables is a little roller to enable small plates
to travel without tilting over the necessary gap between each pair of
bands.
[Illustration: Fig. 8.]
The feeding trough of Cadett's machine is represented in Fig. 8. The
plates, cleaned as already described, are carried upon the cords under
a brass roller, the weight of which causes sufficient friction to keep
the plates from tilting; they next pass under a soft camel's hair
brush to remove anything in the shape of dust or grit, and are then
coated. They afterward pass over a series of accurately leveled wheels
running in a tank of water kept exact by an automatic regulator at a
temperature of from 80 deg. Fah. to 100 deg. Fah., by means of a small
hot water circulating system. The emulsion trough is jacketed with hot
water at a constant temperature. This trough is silver plated inside,
because most metals in common use would spoil the emulsion by chemical
action. The trough is 16 in. long; it somewhat tapers toward the
bottom, and contains a series of silver pumps shown in the cut; the
whole of this series of pumps is connected with one long adjustable
crank when plates of the largest size have to be coated; when coating
plates of smaller sizes some of the pumps are detached. A chief object
of the machine is to deliver a carefully measured quantity of emulsion
upon each plate, and this is done by means of pumps, in order that the
quantity of emulsion delivered shall not be affected by changes in the
level of the emulsion in the trough; the quantity delivered is thus
independent of variations due to gravity or to the speed of the
machine. These pumps draw the emulsion from a sufficient depth in the
trough to avoid danger from the presence of air bubbles, and the
bottom of the trough is so shaped that should by chance any
sedimentary matter be present, it has a tendency to travel downward,
away from the bottoms of the pumps. There is a steady flow of emulsion
from the pumps to the delivery pipes, then it passes down a guide
plate of the exact width of the plate to be coated. Immediately in
front of the guide plate is a fixed silver cylinder, kept out of
contact with the plate by the thickness of a piece of fine and very
hard hempen cord, which can be renewed from time to time. These cords
keep the cylinder from scraping the emulsion off the plate, and they
help to distribute it in an even layer. There would be two lines upon
each plate where it is touched by the cords, were not the emulsion so
fluid as to flow over the cut-like lines made and close them up.
[Illustration: Fig. 9.]
The silver cylinder to a certain extent overcomes the effects of
irregularities in the glass plates, for the cylinder is jointed
somewhat in the cup and ball fashion, and is made in two or more
parts, which parts are held together by lengths of India rubber.
The arrangement is shown in section in Fig. 9, in which A is the hot
water jacket of the emulsion vessel; B, the crank driving the pumps;
C, a pump with piston in position; D, delivery tube of the pump; E,
the silver guide plate to conduct the emulsion down to the glass; F,
the spreading cylinder; G, the cords regulating the distance of the
cylinder from the glass plates; H, soft camel's hair brush; K,
friction roller; L L L, three plates passing under the emulsion tank;
M, knife edged wheels in the hot water tank, N; the "plucking roller,"
P, has a hot water tank of its own, and travels at slightly greater
speed than the other rollers; R is the beginning of the cooling bands;
T, the driving cords; and W, a level of the emulsion in the trough. Y
represents one of the bucket pistons of the pumps, detached. The
construction of the crank itself is such that, by adjustment of the
connecting rods, more or less emulsion may be put upon the plates. Mr.
Cowan, however, intends to adjust the pumps once for all, and to
regulate the amount of emulsion delivered upon the plates by means of
driving wheels of different diameters upon the cranks.
[Illustration: Fig. 10.]
Fig. 10 is a section of the hollow spreading cylinder, made of sheet
silver as thin as paper, so that its weight is light. For coating
large plates it is divided in the center, so as to adapt itself
somewhat to irregularities in the surface of each plate. In this case
it is supported by a third and central thread, as represented in the
cut. Otherwise the cylinder would touch the center of the plate. Its
two halves are held together by a slip of India rubber.--_The
Engineer_.
* * * * *