Automatic Apparatus for Intermittent Washing BURTH. CARROLL, Bureau of Standards, Washington, D. C. HE device here described was developed for washing experimental photographic emulsions, but it may be of value in other cases where the interchange between the solvent and the product is slow and the solvent must be utilized efficiently. A photographic emulsion is normally prepared by precipita tion of the silver halide in the presence of gelatin; after digestion to “ripen” the product, the emulsion is chilled until the gelatin sets to a firm jelly, then cut into shreds or “noodles” and washed to remove the by-products of the reaction and the soluble bromide which is invariably present in excess. For mechanical reasons, the shreds must be at least a few millimeters thick, so that the diffusion of soluble salts out into the wash water takes much longer than from the thin layer of emulsion on a finished plate or film. I n commercial practice emulsions are washed in running tap water, preferably from deep wells for uniformity, and prefer-
- w a t e r inlet
A
ably containing some hardness to reduce swelling of the gelatin. For certain experimental work the use of distilled water, plus a small amount of magnesium sulfate, became desirable for reproducibility. As the batches of emulsion had an initial volume of 1.0 to 1.2 liters, from which 10 grams of ammonium bromide plus other salts were to be removed quite completely, the expenditure of distilled water would be a t best very considerable. The apparatus now in use is shown in vertical section in Figure 1, and the wiring diagram for the clock control is indicated in Figure 2. The emulsion is held in a nickel wirescreen basket in the tank A (made by cutting the bottom off a 3-gallon bottle), The wash water enters and leaves through a two-way stopcock, B , of 4-mm. bore, connected to the bottle neck. The amount of water supplied for each change by siphon from a tank is regulated by the float valve C, which is of the general design suggested by Othmer ( I ) , but with a glass needle to close the inlet hole in a rubber stopper. The valve and float assembly may be slid up and down in the float chamber to regulate the height of water in A . The distinctive feature of the apparatus is the use of the stock two-way cock, turned by a small motor which can be controlled directly by clock contacts. The motor, D ( l / l o ~h. p., 110 volt, 60 cycle, a. c. series wound), drives the stopcock through a worm gear and belt. On the driven shaft, between the driven pulley and the clamp attached to the stopcock key, there are three slip rings. Brushes supported by the same cross strut as the shaft bearings make contact on these as indicated in the wiring diagram, Figure 2. One ring is split in half; each segment is connected with one of the other rings. The clock contacts are alternately connected to the other two rings. When contact is made at the clock, the motor is energized and rotates the shaft 180 degrees. The brush on the split ring is allowed to bridge the gap so that as soon as contact with one half is broken, the circuit is ready to be completed through the other half and the corresponding clock contact.
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WASHINGDEVICE FOR PHOTOGRAPHIC FIGURE1. AUTOMATIC EMULSION 323
FIGURE2. WIRINGDIAGRAM FOR EMULSIONWASHING DEVICE
324
ANALYTICAL EDITION
The shop work involved in construction of the apparatus was no greater than would be required for construction of solenoid valves, and no relays or heavy currents are necessary. The apparatus now runs on a 20-minute cycle, allowing 3 minutes for draining, but it may obviously be adopted to any other timing where the intervals are not too short. Batches of emulsion of 1.2 liters initial volume can be washed to a broN with an expenditure of mide-ion concentration of 1 x loM4 60 to 7 5 liters of water (6 t’o 7 hours a t 5” to 10”(2.). The water is used more efficiently than by an intermittent
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siphon device, since the emulsion is completely covered within a minute after the cock is turned to the inlet position. Provision might obviously be made for stirring the material in the tank; it has been omitted for these relatively small batches of emulsion because the jelly is easily broken up by handling.
LITERATURE CITED (1) Othmer, D. F., IND.ENQ.CHBM.,Anal. Ed., 3, 139 (1931). RECEIVED March 1, 1932. Published by permission of the Director, Bureau of Standards.
Device for Removing “Frozen” Plugs from Stopcocks HARRY W. BAILEY,Bureau of Standards, Washington, D. C.
T
HE successful removal of a “frozen” stopcock plug has frequently resulted in saving valuable apparatus and time. The gain accruing from this simple operation has tempted many chemists to delve somewhat into this, and almost every laboratory has constructed a t least one stopcock key remover. At present, several forms are commercially available from apparatus companies. Although some of these efforts are ingenious and to a degree successful, they possess as a group one distinct disadvantage and one severe
be used in all cases where the stopcock is accessible, and in addition will serve in places not easily reached in a mounted apparatus where the stopcock is placed with the longitudinal” axis of the barrel perpendicular to the plane of the apparatus front. The clamp type (Figure 2) is designed specifically to overcome the limitation of inaccessibility, and is particularly applicable when the remover must be brought to the stopcock. When the cock is sealed into a mounted apparatus so that the longitudinal axis is parallel to the apparatus front (a preferable technic of assembly, especially with oblique bored cocks) , the clamp model may be used in places where no other device will enter. It requires a space equal to the width of the end collars-i. e., only several millimeters. From practical considerations, then, it may be expected to enter any space that the stopcock itself occupies. The device shown in Figure 1 is constructed with jaws (A-A) which are hinged at the points marked 1and 2, and are adjusted by the knurled nut B to accommodate stopcock barrels of various sizes. Pressure is applied to the stopcock S. A. E. Nut B plug by jack screw C, which is threaded is threaded 6/8 S. A. E. and turns on a barrel which is threaded both inside and out. The inside thread fits the jack screw. A fiber plug is inserted in the end of the jack screw and small pieces of adhesive tape are placed in position, as illustrated, to prevent the glass from coming in contact with the steel. This device is very easily handled and will remove the most stubbornly frozen stopcock plug.
FIGURE1. WHEEL-PULLER TYPE
limitation: the lack of quick adaptability to a stopcock of a particular size, which may happen to be any of a wide range of sizes; and the frequent impossibility of applying the remover to stopcocks located in difficultly accessible places. This will occur when the stopcock is sealed into a permanently mounted apparatus which may be so complicated or compact as to prevent the actual placement of the remover around the stopcock. The two key removers described, designed to eliminate these undesirable features, possess certain features which, so far as known, are novel. The “wheel-puller” model (Figure 1) is constructed with adjustable jaws which will accommodate stopcocks of any size without recourse to one of a set of fixed spacers, receptacles, or collars. It is quickly adaptable, may
FIGURE2. CLAMPTYPE
Figure 2 illustrates the clamp type of plug remover. At point D a fiber plug is fitted to bear on the small end of the stopcock plug. The opposing jaw is counter-bored to fit a Bakelite ring which is machined to bear on the stopcock barrel. Parts marked E are Bakelite rings, one larger and one smaller than the one in use on the apparatus in the illustration. It was found that three rings would be enough to cover the range of stopcock sizes in general use in these laboratories. R E C ~ I V March ~D 31, 1932. Published by permission of the Director, Bureau of Standards.
