Glass-Blowing Accessories WALTER A. CARLSON, General Mills Research Laboratories, hIinneapolis, Minn.
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The author has used such a mouthpiece for 2 years and considers i t a great convenience.
ABORATORY glass blowing offers so many difficulties t h a t kinks and accessories developed by one amateur may be of interest to others. Several of these have proved of value in this laboratory, and are described below,
Making Ground-Glass Joints The amateur usually experiences considerable difficulty in making ground-glass joints. I n the conventional procedure the outer cone is easily formed, using a polygonal carbon shaper (Figure 2, a), but the inner cone is prepared by alternate heating and pulling, the final form depending upon skill and guesswork. A poor fit between the cones requires a long grinding time and results in a joint with low mechanical strength.
Glass Blower's Mouthpiece When working with glass i t is often convenient to blow through a rubber tube attached to the apparatus, bit'ing on the tube gently to hold it in place in the mouth. If the tubing is inadvertently clamped shut, closing off the entire system, t,he pressure may increase as the glass is heated until a bubble suddenly blows out, particularly if t'here is a thin spot in the glass. The stem of an inexpensive pipe serves well as a mouthpiece, but sometimes the tongue comes to rest over the end of i t , closing off the system with the same result as aboTe. Gases released froin the glass itself and from deconiposition of material present in the system may be projected into the mouth and inhaled. Ordinarily the gases are not objectionable. Harris and Schumacher ( 2 ) have reported that the main gases released by glass on heating are carbon dioxide and mater, accompanied by smaller quantities of sulfur dioxide, oxygen, and nitrogen. However, if i t becomes necessary t o make repairs on a n apparatus t h a t cannot be cleaned thoroughly, many combinations of gases may be released by thermal decomposition of organic accumulations.
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The mouthpiece shown in Figure 1 is designed to by-pass the gases by the same movement of the tongue that would ordinarily close off the system. The exact dimensions are not important, but a convenient size is indicated. The barrel, A , and the hose nipple, B , are turned from hard rubber, and either threaded or cemented together. The large bore in the barrel is made 0.47 cm. (0.187 inch) in diameter, and tapped with the U. S. Standard 1/4-20 threads far enough to accommodate the brass sleeve, C. The outer end of the sleeve is cut to a cone to form a seat with the brass cap, D. A similar cap and seat, E, are made a t the bit end of the barrel. The valves are seated by grinding with fine silicon carbide. The caps are soldered to a shaft, F , which consists of a suitable length of 0.12-em. (0.047-inch) wire. A soft compression spring placed as shoivn and soldered to the shaft at G normally keeps valve E open. The bit is filed to a convenient shape, as shown at H in the end-view drawing at the left. Section J is deliberately made long, so that the valve extends into the mouth within easy reach of the tongue.
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(d) OF FORMISG INNER FIGURE 2. WEDGEAND METHOD CONE O F T.4PERED JOIST
A good fit may be obtained by a very simple procedure. The outer cone is made in the usual manner, using shapers made from arc carbons or purchased from one of the scientific houses. I t is wise to lubricate the shapers with beeswax, which also prevents them from burning. The inner cone is formed by softening the end of a piece of tubing and then rolling it into shape on a flat surface, supporting the tube at an angle to the surface by the use of an appropriate wedge, such as A in Figure 2, b. Theoretically, for a perfect fit between the two cones, the small angle of the wedge should be equal to angle cy of a. Actually, an angle somewhat greater makes the grinding operation easier. Wood is a satisfactory material for the wedge, which can be cut in any convenient manner. I t is suggested that the cross section be made in the shape shown in Figure 2, c. The rail effect minimizes the tendency of the tube to twist while being rolled. A wedge 10 em. long, 4 em. wide, and 6.5 and 4 mm, high on the high and low sides, respectively, is suitable for tubin up to 15 mm. in diameter. For larger tubing a wedge with fouble the dimensions is convenient. No other accessories are needed. The wedge is placed on a clean, smooth, refractory surface, such as the Transite top of a glass-blowing bench. The desired tubing is placed on the wedge with the end just touching the Transite, in the position shown in b. The edge of the wedge is marked with a wax pencil, at B. If the desired length of joint is C, then another mark, D, is made on the tube a t distance C from B. By guiding D along the edge of the wedge in the rolling operation, the cone is made the correct length (Figure 2, d). The end of the tube is heated t o the softening point in the blast lamp flame and then the tube is rolled back and forth on the wedge with the palm of the hand, following the guide line with the index as described above. It is usually necessary to reheat the glass several times. The tendency of the tube to thicken during the rolling operation can be lessened
FIGURE 1. GLASSBLOTTER'S MOCTHPIECE In use the tongue closes valve E and simultaneously opens valve D, by-passing all the gases to the atmosphere. When blowing is to be done the tongue is removed, thus permitting the valves to reverse and connect the system with the mouth. The mouthpiece may be clamped in proper position and lips applied when desired, as is the practice in some glass apparatus factories. 614
NOVEMBER 15, 1938
ANALYTICAL EDITION
by giving it a preliminary draw to start the taper and then continuing as described above.
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uses is illustrated in Figure 3, a. When sealing a section of the tubing, A, into an apparatus an air-tight, flexible joint may be made a t B with a single turn of rubber tape which is butted together and pinched with the finger tips as in b. After the seal a t C is made, the tape is torn off by grasping the tab, D . Most irregular joints may be sealed by stretching the tape as it is wrapped around the joint. Several turns will seal a stopper in an irregular tube. A convenient temporary repair in a vacuum system may be made by using a technic described by DuMond and Youtz (1) and attributed to Lauritsen and Crane. The organic chemist should find it useful for numberless purposes.
By this method a 10-mm. joint m a y be shaped and ground in about 15 minutes of a c t u a l w o r k i n g time.
Rubber Tape
Literature Cited
A very convenient material, both in FIGURE 3. USE OF RUBBER TAPE glass blowing and in the general laboratory, is ordinary electricians’ rubber tape. It is extremely cohesive, being made of uncured rubber stock. One of its
(1) DuMond, J.
W.,and Youtz, J. P., Rev. Sci. Instruments, 8, 301
(1937). (2) Harris, J J., and Schumacher, E. E., J. 174-7 (1923).
IXD. ENQ.CHEM.,15,
RECEIVEDJune 23, 1938. Paper So. 14 Journal Series, General Mills Inc., Research Laboratories.
Filling Closed-End Mercury Manometers JESSE WERNER, Columbia University, New York, N. Y
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NURIBER of methods have been proposed for filling closed-end mercury manometers without boiling out the mercury inside the manometer (1, 2, 3, 5 ) . However, these methods, although avoiding the difficulties and inconveniences encountered in boiling out the mercury inside the manometer, are either complex in setup or give impure mercury because of contact with grease. I n order to circumvent these difficulties, various manometers, such as that of Zimmerli (6), have been devised which do not have to be filled by boiling out, but in general they suffer from being large and unwieldy or difficult for the inexperienced glass blower to make. By means of a modification of the method proposed by Malmberg and Nicholas for periodically boiling out entrapped gases from the oil in an oil manometer (4), closed-end mercury manometers may be very easily filled. The method is extremely simple and may be used by beginning students on soft-glass manometers, or may be modified to take care of filling more complex manometers, where an all-glass system is desired. Its greatest use probably lies in filling simple manometers for general organic work. The only equipment necessary is a good Hyvac pump and a bulb (or a wide tube constricted a t both ends) large enough to hold in its lower portion all the mercury necessary to fill the U-tube, as shown in Figure 1. The bulb containing the mercury, which should be dry and pure, is attached with pressure tubing to the open end of the manometer and to the Hyvac pump. When the maximum vacuum is attained, the air is driven out from between the glass and the mercury by shaking and tapping. The manometer and mercury may then be gently heated to drive out all volatile matter. When all the air is out, the mercury is carefully poured down into the U-tube and air is let in slowly to fill the manometer. This method may be modified for more complicated types of mercury manometers. For a manometer containing a stopcock the above method may be used or else a bulb may be sealed on between the stopcock and the U-tube, as shown in Figure 2. The mercury in the bulb may then be heated gently to expel the air, the U-tube filled, and the bulb pulled off in
the torch. This arrangement prevents the mercury from coming into contact with stopcock grease. I n the case of a sloping manometer ( I ) , a bulb may be sealed on temporarily and the outfit attached to a mercury diffusion pump. The manometer is then baked out while the mercury is heated, and the mercury is then distilled into the cooled manometer.
Literature Cited (1) Burton, I X D . ENG.CHEM., FIGURE 2 Anal. Ed., 9, 335 (1937). (2) Cameron, Ibid., 5 , 419 (1933). (3) Doja, J . Chem. Education, 10, 574 (1933). (4) Malmberg and Kicholas, Rev. Sci. Instruments, 3, 440 (1932) (5) Weatheril!, J. Am. Chem. SOC.,47, 1947 (1925). (6) Zimmerli, ISD.ENQ.CHEX, ilnal. Ed., 10, 283 (1938). RECEIVED August 10, 1938.
