ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
Inert Atmosphere Dry Box FOR CHEMICAL OPERATIONS JOSEPH M. SHERFEY Electrodeposition Secfion, National Bureau of Sfandards, Washingfon 25, D. C.
B
ECAUSE of the wide current interest in a variety of atmosphere-sensitive chemicals, such as hydrides, borohydrides, and metal-organic compounds, there is a growing need for a device which will permit the handling and chemical processing of such materials without resorting to the fabrication of elaborate and time-consuming sealed systems which are often applicable to only one operation. I n an effort to meet this need, a number of manufacturers (dE, 5E, BE, 10E) are fabricating "dry boxes" of various designs. None of these completely met the requirements of this laboratory, and none included an adequate purifying system for maintaining an inert atmosphere. Thomas and Lichtin ( 2 ) have described a device which would be very useful for certain types of work, but it affords a limited amount of working space and visibility and suffers the serious disadvantage that objects cannot be introduced into or removed from the box without destroying the atmosphere. The apparatus described in this paper has been in operation for about 2 years and has been satisfactory in every respect. It should meet the requirements of most groups that are working with laboratory quantities of atmosphere-sensitive chemicals. Box, Antechamber, and Extension Accommodate Chemical Apparatus and Operations
The entire apparatus can be considered as consisting of two main components, the dry box and the purification train. The whole is a closed system, with the inert gas passing continuously from the box through the purification train and back to the box. The relationship of the various components is shown diagrammatically in Figure 1. The gas passes in sequence through the following components:
1 . Dry box proper with its antechamber 2. Trap for the removal of acidic gases 3. Pump to circulate the gas 4. Apparatus for the removal of oxygen in parallel with a by-pass 5. Heat exchanger to remove heat of compression 6. Two activated alumina dryers in parallel Galvanized steel pipe (1-inch) and fittings were used throughout the system, except for those lines which are shown as a smaller size in Figure 1. These were made of 3/g- or '/Z-inch pipe and fittings. Unions were used liberally to permit easy disassembly of any given section. The following valves are globe type because of the necessity for tight closure, valves 4, 5, 7-14, and 16-20. The rest are gate valves to take advantage of their better flow characteristics. Valves 11 and 12 have been replaced by pipe caps which are screwed off and on as needed. The flowmeters are the aluminum float type and are stock items
@E). The various parts of the dry box, without the gas purification train, are shown in Figure 2. The box proper, A , is essentially a welded aluminum frame, 34 inches high, 72 inches wide, and 24 inches deep with a plate glass front, back, and left end. Laminated plate glass is recommended if there is an explosion
March 1954
hazard. The vertical edges are aluminum angle and the top and bottom are l/r-inch aluminum sheet. A 1/4-inch aluminum plate, B , forms the right-hand end of the box. This plate is held in place by aluminum studs, C, which pass through the frame and are welded in place on the inside. The studs pass through corresponding holes in a rubber gasket (not shown) and then through holes in the end plate. Brass nuts turned onto the studs permit tightening of the assembly to give a gas-tight seal. The hole, D, in the end plate is large enough t o permit passage of the antechamber rim with its a& tachments. Around the periphery of this hole is a ring of studs, E, which supports the antechamber, F , by means of its flange, G . These studs are also welded in place on the inside and pass through corresponding holes in a rubber gasket (not shown) and then through holes in the antechamber flange. This assembly is pulled tight with brass nuts turned onto the aluminum studs. Three hinged bolts, H , equally spaced around the outer (right-hand) rim of the antechamber fit into corresponding yokes, J , on the inner (left-hand) rim of the antechamber extension, K . Nuts with washers tighten against the yokes and thus hold these two members together. When thus bolted in place, the antechamber extension more than doubles the length of the antechamber. The inner and outer doors of the antechamber and the door of the antechamber extension, together with their hinges and closing devices, are identical. The hinges are double acting and attach a t the back in the figure. The lock bars, L,144, and N , hinge a t the top. The lock bar, M , for the outer door of the antechamber is shown swung up and out of the way to permit attachment of the antechamber extension. The door of the antechamber extension is shown closed, with its lock bar down. Pressure is exerted against the door by a screw, 0, which is engaged by corresponding threads in the lock bar. The hinged catch, P, Q, holds the lock bar in place when this pressure is exerted. All three doors form a gas-tight seal by closing against a Neoprene 0 ring gasket recessed into grooves turned into the faces of the rims. The inner (left-hand) rim of the antechamber extension has no such gasket, since it closes against the O-ring in the outer rim of the antechamber. The antechamber, its extension, and the doors must be strong enough to withstand evacuation. Walls of '/a-inch and doors of l / h c h aluminum have been found adequate with an antechamber 15 inches in inside diameter. Attached Gloves, Equipped with Ventilating Device, Permit Manipulations within Box
I n order t o permit manipulations within the box, it is provided with four aluminum ports, R, to which are cemented shoulderlength rubber gloves (,%E,11E). The port construction and the method of attaching these gloves are shown in Figure 3, A , B. The diameter of the cylindrical part of the ports should be
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ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT which has been turned inside out to show the assembly more clearly. -4 rubber tube, A, coming from a source of compressed air feeds into a small, flat, glass manifold, B , which is cemented (423)to the inner surface of that part of the glove which covers the back of the hand. Small rubber tubcs, C ( l / ~inch in inside diameter, or less), lead from the manifold to the ends of the fingers, where they exhaust. A strip of rubber, D,firmly cemented in placr, reinforces the assembly a t its point of greatest strain. When the chamber stands idle for several days without operation of the purification train, the atmosphere of t'ie box is slowly contaminated by diffusiori of oxygen and water vapor through the rubber gloves. T o prevent thesc g a m from entering the box, the glove ports are equipped with detachable, gas-tight caps which, vihen in use, close the ports from Figure 1. Dry Box a n d Purification Train the inside. The caps are removed mh(m the purification train is again opcrating. A = Dry box H = Heatexchanger B = Dry box antechamber J = Flowmeter ( 1 to 10 cu. ft./min.) Gases which have diffused through the C = Acid trap K = H e a t exchanger gloves are then swept' away before tiicy D = Pump-motor assembly with vacuum g a g e I = Preheater can contaminate sensitive chemical*. E = Pressure g a g e (0 to 5 Ib./rq. inch) M = Dryer These caps are also useful in that thcy F = M e t a l bellows N = Flowmeter (3 to 30 cu. ft./min.) G = Apparatus for removal of oxygen P = To vacuum pump make it possible to close off a glove port while a defective glove is being rcplaced. decided after the purchase of shoulder-length rubbcr gloves, The extreme right-hand port in Figure 2 is shown with iicitlicr since these gloves are obtainable in a limited range of diameters cap nor glove in place. The adjacent port is shown with its at the shoulder opening. The poi ts are bonded to the glass Tvith a glove reniovcd and thc cap in place. synthetic rubber adhesive (7E) The same adhesive was used The construction of the caps is Bhonn in Figure 5. The supto seal the glass to the frame. port bar, A, is threaded to engage a screw, B, which terminates Since this box would be ruptured by small changes in pressure a t one end in a knurled handwheel, C, and at the other in a cirabove or below atmospheric, it is equipped nith a combination cular aluminum plate, D. The plate is attached to the screw oil manometer-pressure relief device, S which prevents pressure by a ball-and-socket joint. differences greater than 0.5 pound per square inch. I vertical When in use, the cap assemblj- is supported by two grooved '/$-inch pipe adjacent to S act; as n support. A small, ciosedaluminum pads n-hich are \Tiilded to the inside surface of tho end mercury manometer, T , Ti-as installed to indicate the degree glove port cylinder. Figure 6 s h o w these pads, as seen from of evacuation of the antechambpr. Both of these manometers inside the dry box. Each groove has an enlarged tapered opcnare sealed in by means of packing glands screwed into aluminum ing a t one end, A , and is closed x i t h a stop at the other end, R. couplings which are welded in place. Shown a t C and V ale The stops on the pads prevcrit clockwise rotat,ion of the support 11/2-inch aluminum pipe couplings which are n elded through the bar when the handwhoel is tightened. top and nall of the dry box and act as gas outlet and inlet, reI n order to p u t a cap in place, the machined ends of t,he s u p spectively, for the gas circulating system. Similar but smaller port bar ( E of Figure 5 ) are guided into the grooves in thc palls couplings are in the wall of the antechamber. These are used until they Feat against the stops. The handwheel is then turnod to connect the piping system, as shorn in Figure 1, and to attach clockwise. The screw, having a left-hand thread, forccs the the mercury manometer, T. circular aluminum plate against the inner rim of the glove port Alternating and direct current ekctiical service \vas brought cylinder. The neoprene rubber gasket (F of Figure 5) makes : I through the box wall by means of wax-filled pipe nipples like gas-tight seal. those used to bring the electric leads for the motor through the container ~vall. Such insulated electrical seals are also availSealed Storage Chamber Affords able commercially ( I E ) . Standard receptacles, W , were inMaximum Utilization of Dry Box Space stalled inside the box. The third outlet shown is for a 50-ampere plating circuit. Four valved hose connections, X , permit entry A second dry box n-hich this laboratory is using is equipped of services such as condenser water and vacuum lines. with a sealed storage chamber which has been found very uscful. Shown a t Y is an inverted cylindrical borosilicate glass jar, For example, sensitive materials can be stored in this chamber 12 inches in outside diameter and 24 inches high. This is sealed rrhile the interior of the box is being ivashed. The storage in place over a hole in the top of the box which has about the chamber also makes it possible to keep articles out of the way same diameter as the inside diameter of the jar. The additional and thus affords niaximuiii utilization of the space in t,he dry height afforded by this jar is very convenient when tall apparatus, box. This chamber, as seen from the left front of the dry box, is such as a reflux condenser, is being used. I n order to avoid the discomfort caused by the collection of shown in Figure 7 . Essentially, it is a counterbalanced eleperspiration in the rubber gloves, they were equipped with a vator. The partially lowered cage of the elevatx, A , which is ventilating device. Figure 4 is a photograph of one of the gloves divided into shelves, is shown inside the dry box. On the top
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
Figure 2. Inert Atmosphere Chamber, Antechamber, and Antechamber Extension A = Inert atmosphere chamber B = Right-hand wall
C = D =
Aluminum studs Hole in right-hand wall E = Aluminum studs F = Antechamber G = Flange on antechamber
H = Hinged bolts
S = Oil manometer
I = Yokes K = Antechamber extension
T
L, M , N = Lock bars 0 = Screw through lock b a r P, Q = Hinged catch
R = Glove ports
of the box is the housing, B , which forms the shaft of the elevator. The base of the housing is a flange, C, which is sealed in place by means of a synthetic rubber adhesive (YE). Two lead blocks which travel in channels D a t the front and back of the housing (only the front channel can be seen in the figure) act as counterTT-eights for the cage. These blocks are attached to steel cables which pass over pulleys set in the walls which divide the housing from the channels. The other end of each cable is attached to the cage. The plate, E, which forms the bottom of the cage, also acts as a door &hen the chamber is closed. The four walls of the housing extend downward about 1 inch through a rectangular opening in the top of the dry box. The plate, E, with its rubber gasket, F , closes against the edges of these walls.
S e o l i n g compound
of lhis flange Cylinder
\
g101e
A
Figure 3. s
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I
A.
Section
Glove Ports 5. Front
= Mercury manometer
U =
Gas outlet = G a s inlet W = Electrical outlets X = Hose connections Y = Borosilicate glass i a r
V
A closing device, G, similar to those used for the doors of the antechamber and antechamber extension, exerts sufficient pressure on the assembly t o give a gas-tight seal. Acid Trap and Heated Copper Tubing Remove Carbon Dioxide and Oxygen from System
An acid trap has been found necessary to protect the pump, motor, and other parts of the system. It also eliminates carbon dioxide from the atmosphere of the box. Coarsely granular soda lime (4 to 8 mesh) is a satisfactory absorbent. The trap was constructed as follows. A length of borosilicate glass pipe 4 inches in inside diameter by 24 inches long was fitted a t each end with a blanking flange tapped for 1-inch pipe. This assembly, with the possible exception of the plate part of the blanking flange, can be purchased from the manufacturer of the glass pipe. A bellows relieves the assembly of mechanical strain, and unions above and below the trap permit easy disassembly. Since the box proper is maintained a t atmospheric pressure, the vacuum gage on the pump-motor container indicates the pressure drop through the line containing the acid trap. This is valuable in that it gives warning of any serious clogging of this trap. Pump-Motor Assembly. .4 flow of about 20 cubic feet of gas per minute has been found to be adequate and does not require excessively large equipment, In the apparatus described, a gage presaure of about 3 pounds per square inch is necessary t o maintain this flow, if argon is used as an atmosphere. .&out half this pressure is required if helium is being circulated. A suitable pump for this purpose is the rotary positive type with two interlocking figure-eight-shaped impellers (9E, IdE). The pump is belt driven by a 11/2-hp. electric motor. The packing seals furnished with this type of pump mere found
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ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
figure 4.
Inverted Glove, Showing Ventilating Device
A = Rubber tube leading to source of compressed air B = Gloss manifold C = Air outlet D = Rubber reinforcing strip
to be entirpl>-inadequate for this application; however. Consequently, it x-as necessary t o enclose both pump and mot,or in a gas-tight steel cylinder. This was made strong enough to withstand evacuat,ion. The front plate of the cylinder Iiolts against a flange and is sealed nit11 a rubher gasket. I t is thus removable to permit periodic servicing of the pump and motor. Gas coming from thc acid trap is exhausted into this cylinder. I t is t,hen taken up h y t,he pump and forced through a short length of rubber hose, n-hich is connected to a coupling passing through the cylinder wall, The ruldior hose is used t o reduce the noise of the pump. Several rectangular fiberboard baffles inside the cylinder and riibhrr mount,s for the pump and motor also help to reduce noise. The electrical leads for the motor were brought through t,he wall of the container by means of a device made as follom. A 3/4-inch pipe nipple about 3 inc-lies long was fitted a t one end with a rubber stopper. Three bare S o . 12 copper wires r e r e then passed through t,ightlg fitting holes in the stopper and on through t,he nipple, in such a way that the: touched neither the walls of the nipple nor each other. The nipple was then xarmed and filled with hot high vacuum ~vax. K h e n the wax cooled, the stopper was removed and the nipple was turned into a coupling passing t,hrough and ~veldedto the c>-linder\\-all, A pipe Kith a gate valve Tvhich by-passes tliij pump-motor be a useful addition to the system. container ~+-ould Oxygen Removal. Oxygen is removed from the system by passing the gas over copper at 550" C. The apparatus in which this is accomplished is illustrated schematically in Figure 8. The Vycor tube is about 42 inches long and Z1I2 inches in inside diameter. When operating, the tube is lieat,ed to about 550" C . by means of a thermostatically controlled tube furnace which is not shown. The furnace is the hinged type, 24 inches long, 3inch bore, viith a capacity of 3400 watts. It is mounted vertically in such a position that it surrounds the Vycor tube without touching it and extends from about, 1 inch below the lover end of the top silicone rubber sleeve to the top of the copper cooling coil. 9 n asbestos collar (not shown in the figure) around the Vycor tuhe between the furnace and the top rubher slerve protects the latter from the heat of the furnace. The copper tube shona in Figure 8 is 27 inches long and has an inch less than the inside dioutside diameter about 1 / 4 to ameter of the Vycor tuhe. Its purpose is to support the I/*-
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inch lengths of '/2-inch-dianieter copper tubing with which it is filled. These are not shown in the drawing. Unless supported, these tend to pack and sinter against the Vycor, resulting in eventual breakage. The asbestos ring baffle serves to keep heated gas away from the inner surface of that portion of the Vycor n-ith which the bott,om rubber sleeve is in contact,. The asbestos ring cushion eliminates glass-to-metal contact,. The crossbars a t the end of t,he c.opper tubc (detail, Figure 8) rest on the copper coil and t,hus support t,he tube a i t h its packing. A gate valve (sa in Figure 1 ) controls the flow of gas through this unit. Heat Exchanger. The heat exchanger crhich is incorporated into the lower part' of t,he oxygen scrubber does not completely cool the gas coming from this unit (the temperature of the effluent tem is operating). The gas gas is 80" to .3.00° C. when the coming through the by-pass from the pump is licated to about the same temperature by compression. These two streams unite beyond the apparatus for removal of oxygen and must be t,horoughly cooled before passing through the dryers. This is necessary because the effectiveness of alumina as R drying agent falls off rapidly with increasing temperature. This heat exchanger can be made easily or perhaps purchased.
T w o Dryers Provide Continuous Operation during Regeneration of Aluminum Oxide BE originally constructed, this dry box contained only one dryer containing aluminum oxide. It was made from a 3-foot length of 8-inch steel pipe, mounted vert,icallp and covered with standard pipe insulation. This was fitted with a blanking flange and lead gasket a t the bottom. The top was sealcd with a welded steel plate. This plate TTas tapped in two places for 1-inch pipe opening?. One of these openings serves as a gas inlet, the other carries electrical leads for the heating coils used t o regc?nerat,ethe alumina.
Figure 5.
Glove Port Covers
A = Support b a r B = Screw C = Knurled hondwheel
D
= Aluminum plate € = Machined end of support b a r F = Rubber gasket
The terminals of these coils pass through a nipple turned into this opening and then into a 1-inch union. The other half of the union is screxed to an insulated wax-filled nipple, previously described. The soldered connections betn-een the coil terminals and the line source. feeding through the was-filled nipple, arc inside the union. This arrangement allorvs these connections to be made without twisting the leads. The nipple, which is screwed directly to the top of the drying chamber, should be packed with glass voo1 and fitted with cooling fins. This prevents melting of the %-ax during regeneration yf the alumina.
INDUSTRIAL AND E N G I N E E R I N G CHEMISTSY
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ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT The blank plate a t the bottom of the chamber was tapped for 1inch pipe t o act as a gas outlet. The drying chamber contains about 50 pounds of 8- to 14-mesh activated alumina. A current of hot air is used for regeneration. The air is heated by means of resistance xire wrapped around the inlet pipe ( L of Figure 1) and six large heating coils suspended from an insulated frampwork imbedded in the alumina.
Figure 6.
After all leaks have been eliminated, the system is filled with the inert gas to be used as an atmosphere. This is most easily done in the following way. A very large balloon, such as is used in meteorological work, is inflated with air through one of the valved hose connections until it essentially fills the box. This must be done carefully, since the box is not protected by the oil manometer from the pressure of the balloon against the walls. The inert gas is then passed in through one of the other hose connections, thus deflating the balloon. Alternatively, the balloon can be inflated with the inert gas through one of the valved hose connections and then, after being disconnected on the inside, allowed to deflate. The antechamber and pump-motor container can be evacuated simultaneously and then filled Kith the inert gas. The rest of the system should be flushed. The purifictition train can then be started.
Glove Port from Inside Dry Box
A = Open end o f groove in p a d which supports glove port cover B = Closed end o f groove
The temperature of the regenerating air as it leaves the preheater is read by means of a mercury-in-glass thermometer. This thermometer passes through a gland packed with asbestos and graphite. The gland screws into a tee on the inlet pipe. Stainless steel thermocouple %ellsin the top of the drying chamber and extending nearly to the bottom of the chamber permit determination of the temperature of the bed during regeneration. Electrical connections inside the chamber should be welded, since silver solder is severely corroded. Because the dry box was out of operation while the drier was being regenerated, and because it was suspected that the ultimate dryness obtainable from aluniina m-as not being realized, a new dryer was installed in parallel with the one described. The following changes mere made. The container was enlarged to a 4-fOOt length of 10-inch pipe, a synthetic rubber sealant (7E) was used in place of wax in the wax-filled nipple, the preheater circuit was made separate from the internal heating coil instead of in series with it, the inlet or preheater was made of 1inch copper tubing, and the container %as v-ound viith heating wire, making a third circuit. This arrangement makes it much easier to get uniform heat distribution during regeneration. The smaller dryer is now used as a stand-by and is operated while the large one is being regenerated and v\ hen i t is necessary to remove relatively large quantities of water. These dryers have both given good service, but they are unnecessarily heavy and require frequent attention when they are being regenerated. Gas dryers are commercially available (&E), and it would probably be desirable to buy one as a unit. Testing, Filling with Inert Gas, and Flushing of System Are Essential to Operation
Before the dry box is put into operation, the entire system should be carefully tested for leaks. A very satisfactory way to accomplish this is to fill the system with Freon or a Freon-air mixture under a slight positive pressure. Any leaks can then be easily detected with a device commonly called a halide torch, which is used by the refrigeration industry to locate Freon leaks.
March 1954
Figure
7. Storage Chamber for Dry Box
A = Elevator cage B = Elevtaor housing C = Flange on housing
D = Channel for lead weight E = Plate which forms bottom o f
elevator
cage F = Gasket G = Closing device
When apparatus is to be put into the box, the outer door is opened and the apparatus placed in a wire basket made to fit the antechamber. The outer door i p closed and the antechamber is evacuated through valve 19 (Figure 1). The small, closedend mercury manometer indicates TThen this evacuation is essentially complete. The inert gas is then admitted to the antechamber until atmospheric preesure is obtained. The f l o ~is
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ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT continued until the inner door can be opened, since even a slight vacuum in the antechamber makes it difficult to open the door. \Then volatile materials are put into the box they mufit be contained in a bomb if the evacuation method is used. Otherwise, the antechamber is flushed by passing the inert gas from a cylinder through valve 17 and out through valve 18. After a suitable period, these valves can be closed and valves 16 and 20 opened. This directs a portion of the flow from the purification train through the antechamber and effects a final cleanup prior to opening the inner door of the antechamber.
GAS INLETBELLOWS BRASS CYLINDER SILICONE RUBBER S L E E V E 64 mm i d VYCOR TUBE
HOT JUNCTION OF THERMOCOUPLE
WELDED CROSS BARS
WELDEDCROSS BARS (SEE DETAIL)
OR THERMOCOUPLE TUBE
ASBESTOS RING BAFFLES
SILICONE RUBBER SLEEVE
ASBESTOS RING CUSHION
COPPER COOLING COIL 1/8' BRASS CYLINDER
WATER I N L E T AND O U T L E T
PLUMBING ELBOW STAINLESS S T E E L THERMOCOUPLE WELL TWO HOLE CERAMIC THERMOCOUPLE TUBE
Figure 8.
4~ THERMOCOUPLE LEADS
Apparatus for Oxygen Removal
\Then long objects are to be placed in the box, the antechamber extension is attached. This obviates the necessity for opening both doors simultaneously and thus introducing large amounts of ovygen and \Tater vapor. When the apparatus for the removal oi oxygen is being brought to operating temperature the valve on the by-pass (valve 5a, Figure 1) is opened enough to give that minimum of flow through the Vycor tubc which will protect the upper silicone sleeve from the heat of the furnace. The warm-up period is thus materially shortened. After the temperature of the furnace reaches about 550" C., the valve on the by-pass is partially closed to increase the flouv of gas through the Vycor tube, The heat output of the furnace limits this flow to about 8 or 10 cubic feet per minute. The system can be filled with inert gas and the atmosphere scrubbed essentially free of oxygen and vvater vapor in a peiiod of 8 hours or less. 9 small amount of hydrogen is added periodically to the atmosphere of the dry boy. This is done when a visible oxide film forms on the copper in the apparatus for removal of oxygen. This procedure effects continuous regeneration of the copper but is objectionable because it puts an additional load on the dryer. An alternative method which does not require hydrogen in the atmosphere involves periodic regeneration of the copper. This is accomplished by closing valves 3 and 6 and passing hydrogen or a hydrogen-nitrogen mixture through the hot scrubber, using valves 4 and 5 as the inlet and outlet. Regeneration of the alumina is effected by closing valves 7 and 13 (or 8 and 14) and opening valves 9 and 11 (or 10 and 12). A current of air is then passed into the preheater and through the bed. The heating circuits are turned on and the flow of air adjusted so that its temperature is somewhat less than 315" C.
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as it leaves the preheater. This is continued until the entire brd has been brought to a temperature between 177' and 318" C. ( I ) . Below this range the alumina is not completely regeneraf etl; if heated above 315' C., the adsorptive property of the alumina is permanently impaired. X h e n reactivation is complete, the bed should be allowed to cool and, after the air is flushed out xyith inert gas, is ready for use. Chamber Performance I s Adequate for Handling Variety of Atmosphere-Sensitive Materials
A quantitative estimation of the water vapor in the atmosphere of the box has not been made. The oxygen content was found to be less than the amount determinable by the mass spectrograph, O . l Y , , and is probably very much lower. A stoppered bottle of titaiiium tetrachloride kept in the box affords a very useful, although empirical, test for drynees. If no fumes can be seen when this bottle is opened the box can be coilsidered dry. The ultimate dryness obtainable from activated alumina is about 9 X mg. of water per liter (4 X grains per cubic foot) (1). To effect this ultimate dryness, it is necessary that the alumina in the outlet portion of the dryer be maintained completely free of adsorbed moisture. This is true because the vapor pressure of water above alumina is an approximately linear function of its water content. Continuous recycling doics not achieve the same result as one-pass drying because the entire bed is contaminated with mater instead of only tho inlet portion. In order to achieve one-pass drying it is necessary that the gas flov through the alumina bed not exceed 10 to 20 cubic feet pcr hour per pound of alumina (1). The flow through the sintill dryer was approximately 24 cubic feet per hour per pound of alumina. Even if it is assumed that this flow is vithin the probable error of the above specification, it is desirable that a considerable excess of alumina be used in order that ultimate dryness will be obtained even after the bed has taken up a considerable amount, of water. It is believed that the larger dryer accomplishes this. The apparatus vrill be found adequate for most purposca. Decomposition by water vapor or oxygen of the materials handled in the dry box has never been det'ected. These materials include such compounds as sodium and zinc alkyls and bi- and trivalent titanium halides. Spilled droplets of liquitl sodium-potassium eut,ectic have been observed to retain a bright surface after several hours' exposure to the atmosphere inside this box. Literature Cited (1) Aluminum Company of Aineiica, "Activated Propel ties and Uses" (1949).
Alumina, I t s
( 2 ) Thomas, George R., and Lichtin, Korman N., R5i. Sea. I n s t r , 24, S o 12, 738 (December 1952).
Equipment References (lE) American Phenolic Corp., 1830 South 64th Ave.. Chicago 30, Ill. (pressurized mounting receptacles). (2E) S.Blickman, Inc., Weehawken, N. 3. (3E) Fisher and Porter Co., Hatboro, Pa. (Rotasight flowmeters). (4E) Goodyear Tire and Rubber Co., Akron, Ohio (Pliobond 30). (5E) Charles E. Griffin Co., 555 lliramonte Aye., Palo Blt,o, Calif. (6E) Hewaunee Manufacturing Co., ddrian, Mch. (7E) l\linnesota Mining and Manufacturing Co., 411 Piquette Avc., Detroit 2, 3Iich. (EC-801). (SE) Pittsburgh Lectrodryer Corp., P. 0 . Box 1766, Pittsburgh 30, Pa.
(SE) Roots-Connersville Corp., Connersville, Ind.
(10E) Scientific Service, Inc., 1417 Salano Avo., Albany, Calif. (11E) Surety Rubber Co., Carrollton, Ohio. ( 1 2 3 Butorhilt Corp., 2008 East Slauson dve., Los Angeles, Calif. R E C L I % Ef oDr review May 2 2 , 1953.
INDUSTRIAL AND ENGINEERING CHEMISTRY
ACCEPTEDXovember 10, 1'153.
Vol. 46, No. 3
