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.
[Illustration: FIG. 3.]
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_.
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