Removal of Adhered Rubber Stoppers A. J. BAILEY, University of Minnesota, Minneapolis, Minn.
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an eighth of an inch. As shown in Figure 1, the top of the technician's right hand is rotated toward his body. Since the shank of the file is pinched between the rubber and the glass, which have widely different coefficients of friction, rotation causes the side next the glass to slide, while that next the rubber merely grips the rubber and sinks in. Continued rotation tears the rubber from the glass by lifting the rubber vertically away from the glass surface. After a portion of the thermometer periphery has loosened, the axis of the file (as shown in Figure 1) is shifted by movement of the technician's hand toward his body, so that as the 6le shank moves around the thermometer, it becomes inserted more and more under the stopper until finally the tip a p pears a t the opposite end.
KE method of removing adhered rubber stoppers from
thermometers, Buchner funnels, tubing, etc., is so simple t h a t it appears inevitable that it has been known and used. A search of the literature and a canvass of fellow research men, however, have failed to bring to light any knowledge of existence, and i t would appear desirable to emphasize its unusual effectiveness.
I n this laboratory, no stopper has failed to yield to this treatment. Stoppers which other workers had been unable to remove (without cutting) were submitted as a test of the method and were removed by a file shank quickly and effortc lessly. It has operated on hard stoppers as well as gum stoppers, while size has little or no effect. It is equally effective in removing tubing stuck t o high-vacuum apparatus, and not only has greater ease and speed but is much less likely to break complex glass tubing systems t h a n cutting off the rubber tubing with a knife. Rubber tubing or stoppers close t o a neck or side tube may be removed almost as easily, the only modification necessary being t h a t of working almost one revolution in one direction and then reversing until the side tube blocks the way again, with a little manipulation at a n angle t o loosen the rubber immediately behind the side tube. Partial loosening obtained by some methods necessitates jerking or pulling to remove the rubber, with some probability of breaking. Since the rubber can be completely loosened with a file shank, this danger is eliminated.
FIGURE 1 The only equipment required is a small triangular file, such as is usually used for marking glass tubing before breaking. Holding the thermometer in one hand, the tapered hexagonal shank of the file is inserted under the stopper next to the glass for perhaps
A Method for Assembling Thermocouples H. RI. TRIMBLE, Oklahoma Agricultural and Mechanical College, Stillwater, Okla.
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insulating varnish which is baked on. The sleeving is drawn snugly over the bundle of wires, and its end is cut off beyond the junctions and closed by binding it with fine wires or with insulating varnish, which is baked on. The lead wires are also threaded through a piece of the sleeving, leaving short projecting ends for attachment to the potentiometer. It is then bound to that containing the bundle of wires with fine wire to complete the couple.
RAIDED Fiberglas sleeving, which is coming into use as
a n insulating material for armature and other wires, may be used t o advantage in assembling thermocouples. Suppose that a copper-constantan couple is to be constructed. The leads to the potentiometer will, of course, be of copper. Double cotton-covered, enameled, or asbestos-covered wires may be used, or the individual bare wires may be enclosed in Fiberglas sleeving of small size. As many constantan wires as there are to be junctions in the couple, and one less than this number of copper wires, are cut to the desired length. They are gathered into a bundle, the end is doubled back so that no sharp point is exposed, and the bundle is then threaded through a piece of sleeving somewhat longer than the wires by expanding the sleeving and pushing it over the advancing end of the bundle, then stripping it back. Two additional copper wires to serve as potentiometer leads are introduced near the middle of the length of sleeving surrounding the bundle of wires and threaded through it as before, one to either end. Kow one of these lead wires is attached through a resistance of 100 or 200 ohms to one terminal of any convenient battery, and the other pole is connected through a milliammeter to an exploratory wire. By touching this exploratory wire to various ends of the copper wires a t one end the lead wire is found. It is paired with one of the constantan wires and the two are twisted together and fastened by soldering or welding. The other end of the constantan wire which has just been connected may be found and connected to one of the copper wires. The various wires are thus sought out and connected one after another, the second lead wire being connected last. The lengths of the different pairs should be varied somewhat, so that no two junctions a t one end fall together. The junctions may now be dipped into
Thermocouples assembled in this way are flexible and readily adapted to various assemblies without the necessity of handling a tangle of loose wires, they occupy less space than those assembled in glass, porcelain, or metal tubes, and they are not readily broken. Their insulation permits their ends t o be slipped into wells or metal protecting tubes, with or without paraffin to aid in conducting heat. They have long lives, give relatively low rates of heat leak from apparatus, and are a t least as constant in calibration as couples assembled in other ways. Couples with as many as five junctions have been assembled in this manner and used, but still more complex ones offer no difficulties. Fiberglas sleeving may be had with internal diameters of 0.067 t o 0.5 inch. The 0.125-inch size has been found best for the couples which the author has made. When braided with a small percentage of cotton t o give i t strength it provides satisfactory insulation somewhat above 100" C. When the cotton is burned out i t tends to become brittle and to break when flexed, b u t its intrinsic insulating properties are not impaired. 52
