GLASS-WORKING EQUIPMENT FOR THE SMALL LABORATORY
T h e work of the chemist or the cltemistry teacher i s oflen hnntflered bjj luck of facilities for simple glass blowing. Directions are given for making seeeral types of blast burners from pipe jittings and cop9er tubing at nominal cost. Other items of equipment are described, and a method of annealing .finished work i s fiven.
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The need for some knowledge of glass blowing is probably felt a t times by nearly every chemist, and the increasing use of all-glass apparatus for both research and demonstration purposes may provide a distinct handicap for one whose ability in this line is limited. Nevertheless, many chemists cannot make even the simplest seals, and all too many laboratories possess no glass-working equipment beyond the wing top and triangular file supplied to every student. In other places the passing of a staff member who could "make things" is mentioned with regret, but his blast lamp corrodes on the most inaccessible shelf of the stockroom, and the old foot bellows gathers dust and mildew in a morgue of discarded apparatus. Sufficient skill for the most common manipulations may be acquired without instruction by a reasonable amount of practice following the directions of any one of a number of short texts** on this subject. Indeed, many chemists lose enough time in a single year improvising makeshifts and waiting for the retnrn of small repair job9 to become quite adept. On the other hand, nothing can be done without e uipment, and there is usually small inclination to spend money for apparatus that no one can use efficiently. The items of equipment here described may be easily made a t very small cost and with but few tools and little machine work. The simpler ones may prove valuable in even the smaller high schools, and the list includes all that is necessary for almost any job that a self-taught amateur is likely to tackle. The two items of prime importance are a source of compressed air and a suitable blast burner. A means of utilizing a filter pump to supply a moderate amount of air under low pressure has been EDUCATION (I). Placing recently described in the JOURNAL OF CHEMICAL alarge bottle in the delivery line to serve as a pressure-regulating reservoir improves the efficiency of this device. If more than one blast burner is to be operated, a used electric vacuum cleaner is probably the most economical type of blower. An attachment for converting a T i i l bnrner into a blast lamp may be made from copper tubing such as is used for gasoline lines and standard pipe fittings. The cost is less than fifty cents, and not more than an hour's time
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* Since the acceptance of this paper for publication, the author's address has hem changed to the Department of Chemistry. Iowa State College, Ames. Iowa. * * S e e list of text- on page 208. 209
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is needed for its construction. A sectional view is shown in Figure 1A. The materials required are: 1 s/8" street ell 1 $ / a X tee 1 3/s" to bushing 1 J/s' X 6" nipple
8' I/*" copper tubing 1 straight compression fitting to connect the copper tubing to pipe
The 3/8" X 6" nipple is cut in two, three and one-half inches from one end, and the hole in the compression fitting is enlarged by drilling through it with a I/," bit so i t will slide over the copper tube. The air nozzle is made on the copper tubing by squeezing one end in a vise to a slot about 1/16" wide, setting a small brad in the middle of this slot, and then pressing the tube entirely together around it. The end of the finished nozzle is shown in Figure 1B. Two or more nozzles with different size openings should be made. The parts of the burner are assembled as shown in Figure 1A. The compression nut is screwed down but lightly, so that the soft collar is not firmly set on the air tube, but makes a leakless joint. Then, by loosening this nut, the air tube can be shifted to give the adjustment provided by the sliding sleeve of t$e usual blast lamp. The attachment slips over the tube of a Tirril burner, and rests on a cork ring. No packing is needed to prevent leakage a t this connection. The attachment may be rotated about the burner a t will, and the flame directed a t any desired vertical angle by turning the tee on the street ell. Gas is controlled by the needle valve of the burner, and air by a stopcock taken from a broken buret. By use of a Y-connection on A-Blast attachment for the air tube and two stopcocks, the air may be Tirril burner. B-End of finished air nozzle enriched with oxygen for working pyrex glass. The capacity and convenience of this burner will rival that of most blast lamps now sold for less than ten dollars. A hand torch, which is a necessity for the construction of any large allglass set-up, can be made almost as easily as the table burner just described. Smaller fittings are used and brass stopcocks are needed for control of gas and air. The materials needed are: 1 1
I/,"
I/,'
X I/," X X 2" nipple
tee
1 2
I/."
X l'/zvnipple X 4"nipples
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2
'/a' stopcocks with lever handle and female thread 8" %s"copper tubing 1 straight and 1 ell compression fitting for a/ls" tubing and pipe
The constrnction is shown in Figure 2. This burner may be adapted for table use by attaching it to a sawed-off ring stand with a swivel clamp holder. The "cross fues" used by professional glass blowers can be duplicated by screwing the gas cocks of two or more of these torches into a single gas feed line, and mounting two such batteries FIGURE2.-HANDTORCH opposite each other. For the manipulation of pyrex glass and for other work where oxygen is used and maximum temperature is desired, best results are obtained by mixing the gas and oxygen in the body of the burner rather than a t the nozzle. A torch of this nattern is shown in Figure 3. The figure shows this torch with a double head,,which is very useful for seal-- - -- -. . . . ... . . . . inx. tubes snd to end, tor blowing: bulbs, or for other operations requiring that tubes more than a half inch in diameter be uniformly heated over their entire circumference. This can be easily replaced by a single tip when the work a t hand requires it. The fittings needed are: F r c u ~3.-TORCH IN WHICHGAS AND OXYOEN ARE MIXEDIN THE BODYOF THE BURNER A-Two-piece hose end B-Stopcock C S t r e e t ell >Tee %Compression tee F-Copper tubing &Fine-mesh brass sueen H-Loose wad of fine copper turnings or coarse steel w w l I-Fine-mesh brass screen
2 two-piece hose ends A 2 '18' stopcocks, lever handle and male thread B 1 Street ell 1 , - tee D 1 to I/," compression tee I/,' copper tubing 1 '/*"to straight compression fitting for single tip
c
The stopcocks are placed so that the handles are on the same side of the torch body, i, e., each is
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moved one quarter turn from the position indicated in the figure. To insure thorough mixing of gas and oxygen small disks of fine-mesh brass screen are placed a t I and in the oxygen line a t G, and a loose wad of fine copper turnings or coarse steel wool is placed a t H. The tips may be made like the air nozzles described above, but for some purposes a wide flat tip made by pressing the tube on a metal strip about 1/33'' thick is to be preferred. For large work, tips may be made from 3/g'' copper tubing. This has the same outside diameter as '/8" pipe, so may be threaded and screwed directly into the torch body. It is necessary that the constricted portion, whether round or flat, be two or three times as lon, as on the smaller tips. The fish tail burner usually used for bending tubing is altogether inadequate for the large sizes, and even when monnted in sets is not entirely satisfactory because of uneven heating. A blast burner for this purpose is
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Top View
Air
Gar
FIG^ 4.-BLAST
BURNER FOR BENDING
TUBING OF LARGESIZES
shown in Figure 4. Three rows of holes are drilled as shown in a ten-inch piece of I/%" brass pipe. The holes in the center row are ' / , o n and those in the other rows are '/szt A metal tube that is a sliding fit on the pipe permits closing part of the holes to give any length of flame desired. Air and gas are controlled by separate stopcocks, and the burner is mounted on a floor flange that is screwed to the table or to a suitable wooden base. This type of burner in larger sizes is widely used by the makers of neon signs. The size described is about as large as can be used with the stopcocks ordinarily found on laboratory gas lines. Bending large or thinwalled tubes can be greatly facilitated by filling the portion to be heated with clean fine sand held in place by a cotton plug a t each end. Long bends should be made with the tube laid flat on a piece of asbestos. The sand keeps the glass soft enough to work for a considerable time and tends to prevent the development of strains by retarding the cooling. Asbestos
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fiber is sometimes used for the same purpose, but filling a tube with it is a slow process, and its removal is often difficult. The sand is easily shaken out when thecotton plugs are removed and the amount that adheres to the soft glass is very slight. The operation of a blast lamp with natural gas is difficult because of the ease with which the FIGURE5.-ELECTRICALLY HEATEDRESISTAN- WIRE flame is blown out. The A S p r i n g brass mntact strips usual method of preventB-Pivot C-Binding post ing this is to mix a little >No. 26 Chrome1 wire air with the gas before it E-Leads to current supply enters the burner. An equally efficientmethod is to pass the gas through a small wash bottle containing high-test gasoline. This permits close duplication of the flame range obtained with coal gas and produces a higher tbperature. It also permits adjustment to a smoky flame for giving work a protective coating of soot. Its value for enriching an unusually lean mixture of gasoline gas is obvious. For cutting large tnbmg, particularly of pyrex glass, the electrically heated resistance wire is generally recognized as the most &cient method. Several ways of mounting this unit have been described. The modification shown in Figure 5 permits the tube to be placed in position from the top instead of being inserted from the end, and provides for automatic closing of the circuit when pressure is placed on the wire. A small transformer of the typeused with toy railway systems is an almost ideal current regulator for this device. The annealing of hished work often presents almost as much trouble to the inexperienced as the making of a satisfactory joint. The directions frequently given provide that the pieces should be well coated with soot before they are put together, and that all the nearby area should be kept hot while the joint is being worked to shape. When the seal is finished, it is uniformly heated in a FIGURE0 . - C O O L ~ G large brush flame until the soot is burned away, and TRAYS
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then immediately resmoked. It is next slowly cooled in the hot air above the burner, and finally wrapped in cotton for complete cooling. The process consumes considerable time, and troubles beset the novice a t every step. The hot glass may sag out of shape while his attention is given to adjusting the burner; the brush flame may soften the glass enough to cause collapse; careless or hasty manipulation above the burner in the cooling stage may cause strains to develop that will defeat the purpose of the entire operation; and finally the hot glass may set the cotton afire with the almost certain destmction.of the finished piece. Most of these dangers can be avoided by providing two extra burners for the heating operations, and replacing the cotton wrapping with a cooling tray filled with asbestos fiber. A Fisher burner is very good for the general heating, and a Timl burner with a wing top for the smoking. The former should be adjusted to a yellow flame for working soft glass and to its maximum temperature for pyrex. Gas for the Timl may be enriched with gasoline as described above. The cooling trays are made of sheet metal cut in the shape shown in Figure 6 and with the sides turned up along the dotted lines. A sheet of asbestos is placed in the bottom and covered with a quantity of asbestos fiber. The U-shaped notches accommodate pieces longer than the tray. Annealing pyrex glass is sometimes omitted altogether, but the beginner will find the general heating of a joint advisable though smoking and wrapping are unnecessary. Literiature Cited HOSHALL, "Apparstu for Supplying Air bnder Pressure," J. CHEM.EDUC, 7, 2674 (I) (Nov., 1930).
