This section is from "Scientific American Supplement Volumes 275, 286, 288, 299, 303, 312, 315, 324, 344 and 358". Also available from Amazon: Scientific American Reference Book.
The apparatus hereafter described is in general use, and was invented by Herr Paul Grundner, of Berlin. It is particularly adapted for finely dividing large quantities of emulsion. It consists essentially of a wooden lid, a b, fitting upon a large stone pot, to the under side of which two strong trapezoid pieces of wood, e d and e f, are fixed, in the under part of which semicircular incisions are cut and held together by two leather straps, supporting a strong, easily-removable iron transverse bar, g h. Through the center of the lid, and turned by the crank, m, passes the axle i, which ends under the lid in the long ring, n.
The stiffened emulsion is then placed in the bag, o p q r, made of fine but strong canvas, with meshes about 0.5 mm. (such as is used for working upon with Berlin wool). The iron rod, g h, is then slipped through the four loops at the bottom of the bag, the open end is slung upon the ring, n, and bound tightly to it by the ribbons, r1. The loops upon the iron bar are then pushed as close together in the middle as possible, and the stone vessel is filled with water until o p q r is completely covered. The crank is then turned, by which the bag is wrung, and the emulsion squeezed through the meshes immediately into the water. When this process is continued until the purse between n and g h feels like a metal rod, the best part of the emulsion has been squeezed through, and if one now take out the bag and dissolve its contents, it will be found that the loss of emulsion is almost nil.
It may be remarked that the whole apparatus, with the exception of the crank, must be coated with asphalt varnish; also that the corners, r and q, must be separated off from the purse, as shown by the dotted line, s s s s, otherwise the emulsion would lodge there without being squeezed through. Instead of g h a strong glass rod may be used for small apparatus; but for large apparatus it is indispensable, as the power that requires to be exerted would be far too great for glass.
The fundamental idea of the apparatus shown in Fig. 3 first occurred to Herr Jos. Junk, of Berlin. In the present form all the subsequent improvements made by Herren Carl Such, Paul Grundner, and others are incorporated. It may be described as follows:
A tin vessel, the bottom of which sinks at e into the shape of a funnel, rests upon strong iron feet, f f, and is covered with a lid, having a double edge closing it light-tight. Through the center of the lid passes the tube, g h, by which the water enters. In the interior of the vessel upon iron hooks stands a wooden vessel saturated with paraffine, open at the ends, and over one end of which the finest hair cloth is stretched at o p. The water which enters the vessel runs off through the siphon. The proceedings are as follows: Turn the granulated gelatine and the water in which it is contained into the horsehair sieve, m n o p. Place the lid upon the apparatus and turn on the water. The whole apparatus fills with water until the siphon begins to act. If the diameter of the siphon be properly measured--one inch should be sufficient for the largest apparatus--and the cock by which the water is turned on properly adjusted, more water will run out by the siphon than runs in through the supply pipe, and the apparatus becomes completely empty.
The siphon has then performed its function, the apparatus fills again, and the play begins anew. The tube, g h, which reaches right down nearly to the bottom of the sieve, takes the water so deep into the vessel that, as long as the water in the apparatus stands high enough above o p, the gelatine nodules are in continuous motion. In order to prevent the finest particles of the emulsion from stopping up the pores of the sieve too much, and thereby incurring the danger of the water in the sieve overflowing its upper edge, thus occasioning loss of emulsion, the tube, g h, is now sometimes omitted and replaced by a supply pipe, represented in the diagram by the dotted lines, x y. In this way every possibility of loss is excluded, and yet a very careful washing provided. Then when, after being emptied by the siphon, the apparatus fills again, every particle of the emulsion which might have formerly been pressed down into the interstices of the sieve would now be driven up again by the upward pressure of the water entering from below, and thus the sieve would always be kept clear and open.
The great advantages of this apparatus are as follows: 1. From the moment the lid is closed one can work by daylight. 2. The method of washing in moving water is combined with that of complete change of water. 3. The emulsion never comes in contact with metal. 4. Whoever wishes to prepare dry gelatine only requires, when the washing is over and the vessel perfectly emptied, to leave the emulsion to drip for a time, and then to lift out the sieve and its contents and place it in a suitable vessel with absolute alcohol. The latter should be changed once, and when sufficient water has been extracted the sieve should be withdrawn from the vessel and the emulsion allowed to dry spontaneously. In this way all trouble occasioned by changing from vessel to vessel is avoided, and there is no loss of material.
This apparatus is principally valuable in dealing with large quantities, since it saves a great deal of labor, and affords perfect certainty of the emulsion being well washed. It may not be unnecessary to maintain that the difficulties of perfect washing--particularly if one do not wash with running water--increase at least in quadruple proportion to the quantity of emulsion manipulated.--Franz Stoke, Ph.D., in Br. Jour, of Photography.