A d d i t i o n of
Solids
t o Reaction Mixtures
E L I J A H SWIFT, JR.~,AND J O H N H. B I L L M A N , Indiana University, Bloomington, Ind. tachloride, sodium amide, and solid carbon dioxide. When solid carbon dioxide was used, a groove w u cut in the rubber gasket in order to prevent pressure increase in the hopper.
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H E selection of a suitable method for adding solids to reaction mixtures is a problem which often confronts the chemist, particularly when the solid must be added gradually throughout the course of a reaction or it is nececlclary to use a sealed system, so as to exclude moisture. Types of apparatus designed to handle this problem in the research laboratory include the one suggested by Fieser (8) in which the solid is placed in an Erlenmeyer flask connected to the remtion vessel by a large rubber tube, and that of Webster and Dennis ( 4 )which consists of a hopper with a ground-in valve a t the bottom. Dennis and Anderson ( 1 ) have also described a hopper and valve arrangement for the addition of solids. Stock and Guttmann (3)have utiliied a vertical screw to feed powdered material from a hopper into a reaction chamber, making use of a mercury seal. I n the course of research work in this laboratory a new device (Figure 1) was constructed for the intermittent controlled addition of solids to reaction mixtures.
Where it is desirable to add the material continuously, the apparatus shown in Figure 2 operates well. This is designed to add solids to sealed reaction mixtures a t a steady rate over an extended period of time, and once started, will do this automatically. The system can be kept sealed at all times, if an airtight hopper is used to feed the apparatus. Since it is constructed entirely of glass, corrosion is avoided. Construction ia not difficult for anyone with moderate skill in glassblowing.
The device can be 6lled with a solid and attached to the reaction vessel by the round joint a t the bottom, y raising the lunger to the a propriate l e i ht any d e s i r 3 amount of %e 'solid may be made to flow into Figure 1 the reaction vessel, and the flew can be completely sealed off by merely twisting down the plunger until the rubber ring stops the opening. The seal is tight enough to keep anhydrous aluminum chlonde for several h o w without any perceptible reaction with moisture. The extension of the plu er to the tip of the joint prevents caking in the constriction. Zaking in the hopper may be overcome bv cuttine the rubber gasket with a sawlike upper e"dge whi;h may be twisted to loosen the cake. The hopper ma be refilled during a reaction without breaking d e seal by lifting the stopper while holding down the pipet. This apparatus may be constructed readily from glassware often discarded-chi ped flasks and pipets with broken tips. The t&mensions on the drawing are for a model used in this ratory. Another was made from a 2Wml. Erlenmeyer flask and a 25-ml. pipet, and larger sizes could be constructed. If solventa which attack rubber are used a neoprene be substituted for the iubber one. ' I k ~ ~ ~ k ~ cut from a piece of rubber tubing of such a diameter as to fit the ipet snugly. The rubber tubing at the top is lutricatedwith castor oil to make an airtight joint which will allow free movement of the plunger. The authors have found this apparatus to work very satisfactorily for sodium carbonate, anhydrous aluminum chloride, phosphorus pentoxide, red lead, phosphorus pen-
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The solid material is moved forward in a glass tube at a constant rate by means of a close-fitting rotati glaaa spiral. The material drops from a hopper onto the s p i r 3 and is carried forward to drop from the other end into the reaction flask at a rate which can be controlled by varying the speed of the motor turnin the spiral. %he dimensions of the a paratus in Figure 2 are those used on a successful model in this Taboratory, but the size can be varied readily; it is well to retain the thick center axle which is necessary for strength. To make the spiral, a piece of 10-mm. Pyrex rod is held in the ri ht hand and about 40 cm. of 5.7-mm. rod in the left hand. T%e two are sealed together at the end, and the joint is annealed in an air flame. The spiral is then made by heating the smaller rod close to the point of contact with the larger, holding them BO that the angle between the axes of the two rods is about 60°,and rotating the larger rod aa the small rod softens until about five turns have been made. The distance between turns will be about 3.3 cm. The smaller rod is then pulled away and the end sealed to the larger rod and annealed. If any difficulty isencountered in makin the turns an equal distance apart, a spiral made with the spaces%etween successive turns slightly less will work equal1 well At this point, the spiral is too lar e to enter the tube, an8mus; be ground down slightly to a snug i t . This is readily done on a power fine-grained grinding wheel holding the spiral lightly against the wheel with the thumbs in back of it, and rotating it slowly in order to move it evenly am099 the wheel. Hi h places in the spiral can be readily felt and smoothed down and &e whole gradually decreased in diameter until it will almost slide into the tube. It is then ground into a smooth fit with Carborundum, using another tube of the same size. It takes about 3 hours to make the round spiral and the holder. In atta&ing the joint to the tube in which the spiral fits, care must be taken not to let it sink in at any oint. The ground p t s sbown are not eeaential and some flexibihy might be gained y joining the apparatus to the reaction system with snug rubber instead, I n place of the upper joint a hopper could be g k l z o n or a hop r like that shown in Figure 1 used. The seal at the back end o E h e apparatus is made airtight by lubricating
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Prment address, Explmivm Rsaearch Laboratory, 4800 Forb- St., Pittabwgh 13. Pa. 1
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ANALYTICAL EDITION
Septemhsr, 1945
placed on the rod. The authors' model was driven hy a 0.125-h.p. motor, operating at 1525 r.o.m.. connected with B 40 to I reducine eear. The pulley on the ;educing gear was p l a d below the &ley on the shaft of the apparatus, and the connecting belt kept taut hy allowin= Dart of the weieht of the motor and reas to hane from the belt. TI% bearing at thz end of the Pyrex rGd which e&sists of sheet asbestos lubricated with graphite supports most of this weight. When anhvdrous aluminum ohldidc. nhosnhorus oentachloride. and sodiu& carbonate were used thk'sysiem al&ya operated smoothly with no tendency to stick. I
601
aluminum chloride per minute. *? .^
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(1) Dennis. L.M., and Anderson, R.P..J . Am. C h . Sm.,36,882 (1914). (2) Fi&-L., "Experiments in Organic Chemistry". 2nd ed.. Part 11, p. 311, New York. D. C. Hseth and Go.. 1941. (3) A.. and Guttmann. 0..B e . . 37.m y15 (1904). , ~Stork. , (4) webster, 5.H., and D&kii,'L. ni... I . Am. Chon. Sm..55, 3234 (1933). ~~~~
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All-Glass ! ROBERT P. > American Smelting & Refining Company, Cenb
IN
A recent article ( 1 ) an all-glass stirrer wss pictured which is compact, inexpensive, easy to construct, and eliminates the danger of contamination of the solution by corrosion products from an electric motor. The device is not suitable for agitation of large volumes, nor of heavy viscous liquids,'but is extremely useful for sgitation of volumes such as are constantly used in analytical work. I n electrometric titrations the electrodes may he attached to the stirrer, thus eliminating the cluttered condition normally encountered in eleetrometric operations. A method of attaching eleotrodes is shown in Figure 1.
The small T which furnishes the wer to drive the shaft, is connected to it kith a Bhort length oi%bber tubing, which mmes as universd joint, to abeorh stresses due to a r m a t e shaft alignment, makes disassembly Dwihle. and mitS au to lets thmu h the hole in the cente;. T i g k or bind ing bearings will not o rate, but alight high spots may be q,iicklv eraund t o fit. g o ereat clearance results in air leak+l e wi-th-poor performance.
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Figure 9.
Diagram
Stator. A . 14-mm.tubing 11cm. Ions. 8. 8-mm. tubin.. 7 ck 8 cm. Figure 1.
All-Clan Stirrer
Stirrers of the type described are available commeroidy but cannot be disassembled for cleaning or lubricating. Foreign particles, particularly rust scale, may came through air lines and lodge between bearings and shafts, seriously affecting the efficiency of operation. Oeeasionally broken parts cannot be replaced on commercid stirrers. The stirrer is an airdriven type operating on low prmure (not over 10 pounds) on the pinwheel or rocket principle (Figure 2). The stator is a T-tube fitted with rubber stoppers which are bored to accommodate g l w bearings. The rotor is in two parts.
lubricated with a droo of mediwn oil before 88semhly and ocoasionally thereafter. Oil of S;A.E. 30-40 is satisfactory. When the unit is aasembled, stoppers should be adjusted by rotating until minimum bind and friction are obtained and the shaft turns freely. A p r o p e r l y digned stirrer should turn when blown by mouth. T h e d a n g e r of t h e rotor's d i s i n t e g r a t i n g while in operation is extremely remote. Dozens of these stirrers have been made and wed in this laboratory under d l kinds of conditions. The only breakage encountered has been in electrometric titrations, where the rotor has been shattered hy contact with the buret. To prevent this, smell pieces of rubber tubing extanding slightly beyond the ends of the rotor, and with hales eorrespouding to bole locatioas in the rotor, may be installed. LITERATURE CITED
R. P..and Ziechkau, 0. C.. im. ENO. Carnu.. ANAL ED.. 15. 281 (1943).
(1) Yeok.
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