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soted wood. The sheath of many miles of cables underwent a partial conversion into white lead via the classical Dutch process which, though highly regarded by paint manufacturers, became anathema to telephone engineers. The difficulty was met by fumigating the ducts in service with a dilute ammonia-air mixture and by choosing a less acid and more easily treatable wood for future construction. Underground corrosion of other metals, notably of iron and steel, is also often serious. I n the alkali soils of the Southwest anchor rods for telephone poles have sometimes corroded through in a few months. Marshes represent another severe exposure for iron and steel, as, for example, in the form of loading coil cases. A newly introduced form of telephone cable for direct burial in the soil demands careful consideration from this standpoint. A variety of protective finishes, chiefly of asphaltic or pitchy nature, have been studied in this connection. Some remarkable cases have been noted, in which a finish that proved to have a superior protective effect in one highly corrosive soil was worse than useless in another soil which had been regarded as less corrosive in the general sense. The chemistry and physics of soils from many areas has required attention with the control of corrosion as an object. Particle size, saline content, and composition of subsoil atmospheres each has an influence. I n a like way the telephone chemist must concern himself with atmospheric causes of corrosion in equipment above ground, especially in central offices. Moisture and dust contribute to electrical leakage from point to point through the complicated assemblies of electrical equipment. Corrosion products of such leakage may build up a t critical points and interfere with contacts, or essential though usually minute portions of equipment may be etched away. Even faint tarnishes on metallic contacts can so increase contact resistance as to imperil signaling. In industrial areas soot and traces of sulfurous gases add materially to these hazards. Finishes
It is partly to avoid such difficulties and partly for the equally utilitarian purpose of a good appearance that metal telephone apparatus receives some special form of finish coating, whether paint, varnish, lacquer, or electroplated surfacing. I n the selection of such finishes we have drawn
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heavily upon the scientific work of our confrkres in allied fields, but have still found ourselves faced with peculiar difficulties. A great deal of the truly excellent scientific work on finishes has been done by manufacturers with the idea of disclosing uses which will justify the sale of a particular material. But comparative data on the durability of very dissimilar finishes, as, for example, galvanized coatings in contrast to cellulose lacquers, are usually lacking. The fact that finishes are often used primarily for decorative purposes on relatively short lived articles has limited the study of the durability of such coatings. This is reflected in the fact that nearly all the scientific work in this field refers to outdoor exposures where corrosion tends to occur rapidly. Indoor exposures are commonly regarded as so mild as to be negligible. Changing fashions, as in the case of furniture, oftJen bring an obsolescence so early as to be prohibitive were similar consideration to be applied to telephone plant. The prevalent custom of trading in one’s motor car for a new model each year is a factor in another large industry involving extensive use of finishes, which tends to put great emphasis upon initial beauty rather than permanence over periods of ten to twenty years, such as must be considered in telephone plant. With the manufacturing and operating telephone companies tied into a single system, in which the Bell Laboratories’ responsibility is to insure quality of product, there can be no unloading of defective apparatus upon the consumer, for the manufacturer is liable in the last analysis for defects which may appear only after years of use. These considerations have received special emphasis in the discussion of finishes because they afford an excellent illustration of the point. The same sort of considerations, however, apply to nearly all the problems with which we are concerned, to such an extent that our chemical staff is widely thought of in our own organization as a group of specialists in the “permanence” of materials. Such an emphasis by the general management upon ultimate economy rather than first cost alone would doubtless be welcomed everywhere by thoughtful technical men throughout the country. It is a source of peculiar pride to the staff of the Bell Laboratories that the nature and organization of their business is such as not only to permit such an attitude but also aggressively to promote it.
Large Glass Distillation Equipment’ D. F. Othmer EASTMAN KODAKCOMPANY, ROCHESTER, N. Y.
N MANY experimental and small manufacturing operations there is a need for distillation equipment of a larger size than the usual laboratory units. It wa,s to fill this need and at the same time to provide an apparatus of glass
I
which may be used with practically any combination of liquids without corrosion or contamination that the present equipment was designed. Numerous reports have been made describing laboratory distillation apparatus, and the theory and efficiency under different operating conditions have been studied; but usually the apparatus has been used either for analytical purposes or for theoretical studies and is complicated in design and operation by testing devices. The present demands call for simple rugged equipment requiring the minimum of attention and manipulation. 1 Received
January 16, 1930.
I n the distillation of some materials, especially certain organic solvents, the rubber or cork stoppers customarily used for connecting pieces of apparatus are attacked and disintegrated by the hot liquids and vapors. To eliminate this objectionable feature, connections are made with flanged glass ends, rubber cushion backing rings, and aluminum split flanges such as are used for glass pipe. This type of flanged joint2is shown in Figure 1 at L and the aluminum backing ring is indicated in the insert sketch, Other fittings and glass stoppers have been ground to fit where ordinary corks are unsatisfactory. 2 Furnished by Corning Glass Works, Corning. N. Y. The flanged ends, including some 15 cm. of tube length, are made in molds and fused t o tubing.
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thermometer, for charging, etc., are blown in the upper wall of the flask. A 12-liter flask is rather small for this sized Two of the columns described are packed and the third is column and a 22-liter ring-neck Pyrex flask has ordinarily of the bubble-cap type. Except for the glass Raschig rings been employed. The neck of the larger flask is approximately used as a filling material, which are cut more readily of soft the size of standard 76-mm. (3-inch) Pyrex flanged pipe and may be connected to the double-flanged reducer of Figure 2 glass, all the parts are fabricated entirely of P J ~ : x . ~ The packed column M (Figure 1) is Constructed of a with split flanges. When the use of rubber is not objecstandard length of 50-mm. (2-inch) Pyrex flanged pipe 1830 tionable, the fitting blown as shown in R, Figure 1, is inserted mm. (72 inches) between flange faces. Four insealed inlets of through a hole in a stopper fitted to the flask. The lower 12-mm. tubing allow feeding the column at various heights as end is drawn to a 5-mm. tip to allow wash liquid to descend desired. Since it is impractical to make connections in the without priming and the vapors are admitted through four heavy cast end of this pipe, the top connection, X, is insealed holes blown in the side of the tube just above the tip. For below the weld between the cast end and the drawn tubing continuous operation and withdrawal of the residue liquid and brought up over the packing rings, where it opens into at the column base, a 22-liter flask with a bottom outlet and a small four-weir overflow. The other connections, P , are glass cock of 10-mm. bore has been provided. This is used simple inseals with about 20 mm. of tubing inside the column only with the internal heater, to be described. A larger column of greater capacity has been constructed of at an angle with the horizontal. Raschig - of about 30 degrees a n 1830-mm. ( 7 2 - i n c h ) rings cut from 8-mm. soft length of standard 76-mm. glass tubing are used as fill(3-inch) Pyrex flanged pipe, ing material. A small glass Distillation columns and accessories constructed of packed with glass Raschig “ h a t , ” Q, supports these glass of a larger size than have previously been used are rings a n d similarly conand is blown and flared as described, Connections are made with Pyrex flanges nected to the r e s p e c t i v e s h o w n to fit between the and the equipment is substantially all glass, simple and parts of the system. Bel o w e r flanged connection ruggedly designed. This equipment has proved escause of the size of the colwith the still pot. The uppecially valuable in experimental, development, and umn no c o n n e c t i o n s for per two rings of holes allow small manufacturing operations for the preparation of feeding or s a m p l i n g a r e vapor passage and the three quantities up to several hundreds of liters of various made in the tube wall. lower orifices p u s h e d i n liquids by distillation. Flexibility and interchangewards drain the liquid colBubble Cap Column ability of the parts described make possible the arlected on the outside of the rangement and study in miniature of the most intriMany types of glass colhat without priming. The cate of continuous distillation systems for experimental umns depending for their acg a s k e t s above and below or development work. tion on the bubbling of asthe flare of this hat and in cending vapors through a other joints are of gum rublayer of descending liquid ber 5 mm. thick when rubher may be used. When liquids with a solvent action for have been described. Most of these have not provided rubber are handled, all gaskets are cut from thin asbestos definite paths for the two countercurrent streams. The sheet. The asbestos is moistened with water to soften the felt column of Clarke and Rahrs ( 2 ) satisfies this requirement and makes a very tight joint when the bolts through the back- perfectly, but has two other disadvantages as compared to commercial columns: (1) The bubbles of vapor issue from a ing flanges are tightened. The necessity of preventing heat losses from the external single large opening rather than from many small ones; and surface of a column is vel1 recognized-see, for example, (2) the heat loss is excessive and difficult to prevent by adeHausbrand (3)-and is especially pronounced in the case quate lagging due to the irregular external surface. Of the of a small column where the ratio of wall to cross-sectional several variations described by Bruun ( I ) , the one last dearea is large. The two best methods for the prevention of scribed is most adaptable to the present usage. It does not heat losses are the blowing of heated air through a casing sur- entirely eliminate the second of the above-mentioned objecrounding the column and the enclosure of the column in a tions and has an additional one of unfastened internal parts vacuum jacket. There are numerous references t o both meth- which may rattle and become broken in handling or use. The design of Figure 3 is the result of many attempts in the ods in recent literature. The firqt more than doubles the attention required and the second is impractical for units as last two years t o fabricate a simple self-contained unit. In large as these. For distillations below 150” C. practically use it has proved very satisfactory, and both its capacity and equal efficiency and capacity may be secured by the enclosure rectifying efficiency are high. The construction and relaof the column in 85 per cent magnesia insulating material tive dimensions of the several columns now in use are apparent and for these columns lengths of standard pipe covering, 0, from Figure 3. The trap-and-plate assembly are blown toare used. For preparation or manufacturing distillations gether in a unit before assembling in the outer tube. Ten or and all experimental work except precise studies of column twelve holes approximately 4 mm. in diameter pass streams operation and efficiency, this method of heat insulation is of fine bubbles m-hich efficiently wash the liquid on the plate. The arrows drawn in the upper plate assembly indicate the recommended. Three types of connections to still pots have bem employed, path of rising vapors, those in the lower indicate the depending on the requirements of the particular problem, path of descending liquid. The overflow from the renter of The neck of a 12-liter Pyrex ring-neck flask is approximately the flat top of the boiling cap is discharged through the lower the diameter of the 50-mm. (2-inch) columns and a split trap, vented to prevent siphoning, t o the three small outlet backing flange may be placed around the ring neck. The tubes (represented as two on the drawing). These outlet flask is then clamped directly to the column with a suitable tubes come within 1 mm. of the tube, and this proximity and gasket between flange faces. Openings for the insertion of a the surface tension of the liquid allow the liquid to flow down the inner wall to the next lower plate. Alternate plate sec3 The rather intricate and heavy glass-blowing operations were satistions are provided with side tubes for the feeding of liquids or factorily completed by the Technical Glass Company, of Rochester, N. Y , vapors, the withdrawal of vapors, or the insertion of therwhich company is prepared t o furnish these units, including the glass Raschig rings, in the described or smaller sizes mometers. The columns have been made in units of four, Packed Distillation Columns and Fittings
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six, and eight p l a t e s with glass flanges on the ends for assembling. By connecting these sections together columns of any practical even number of plates can be made as required by the p a r ticular problem. This feature is especially advantageous for experimental work with continuous distillation systems where several columns are to be interconnected in various ways. In some distillations it is desirable to be able to stop the operation of the column without d r a i n i n g the plates. The volume of liquid held on the plate between the cap and the inner column wall is somewhat less than the volume which c a n b e retained under the cap. Thus, when heat is no longer supplied to the still pot and the cond e n s a t i o n of vapors causes a partial vacuum there, the liquid held on the plate is drawn under the cap and gases or vapors bubble up through this liquid and thence pass down the “ r i s e r ” or “thimble” tube. If it is necessary Figure I-Distillation Apparatus w i t h to eliminate any possiPacked Column bility of such “siphoning,” this can be accomplished: (1) by making the diameter of the cap larger in relation to that of the column, thus decreasing the amount of liquid held up by the plate and increasing the capacity under the cap; (2) by decreasing the height of the lower trap so that it is less than that on the plate and vapors may be drawn down the overflow tube; or (3) by placing an auxiliary trap on the still pot, which will allow air to come in at the column base on a shutdown. This last method of “vacuum release” is often found on large equipment. Condensers
The dephlegmator and final condensers (Figure 4) are blown in a single unit and are enlargements of the type previously described ( 5 ) . The dephlegmator consists of two coils of 8-mm. tubing in series installed in a 400-mm. length of 60-mm. tubing with flanged end. The outer coil consists of fourteen turns 46 mm. outside diameter and the inner coil of twenty turns 26 mm. outside diameter. Three connections for cooling water are attached through the wall, D and E a t the top and F a t the seal between the coils at the bottom. By plugging one of these openings and using the other two as inlet and outlet, respectively, it is possible to use either of the coils separately or the two in series. With the lower tube
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as inlet and the two upper tubes as outlets, the two coils are connected in parallel. This choice of connections allows wide latitude in the control of the amount of reflux. Both water and air have been used as the cooling medium, and the use of air allows very sensitive control when only a m a l l amount of heat is to be removed. The large amount of wetted surface in the dephlegmator adds materially to the efficiency of the rectification, since the vapors going to the final condenser pass up and around the maze of wetted coils. Condensate dewending this type of coil is thrown to the walls by centrifugal force and, in order to collect the condensate to a center drip for observation, the short tube below the dephlegmator is flared and insealed to the condenser wall as shown a t H , Figure 4, with a condensate tip and four vapor holes blown to prevent priming. The vapor outlet from the dephlegmator is a short section of 38-mm. tubing sealed into the 85-mm. casing of the final condenser. The condensing surface is of 10-mm. tubing and consists of thirteen outer turns 60-mm. outside diameter and sixteen inner turns 35 mm. in diameter. These coils are connected in parallel a t their upper and lower ends to the water leads. The condensate outlet of the final condenser, .I, is a 30-mm. length of 10-mm. tubing sealed in the bottom. A short section of heavy-wall 22-mm. outside diameter tubing is welded a t the top of each condenser jacket and ground for glass plugs. The one above the dephlegmator, G , supports a thermometer and the one above the final condenser is sealed to a vent tube, C, with open end near the water inlet. This vent tube is useful only when it is desired to run the condensate in a full stream without entrainment of air or vapors. For use with columns having standard 50-mm. (2-inch) Pyrex flanges this condenser system is clamped on as shown in Figure 1. With the 76-mm. (3-inch) packed column the reducing fitting, Figure 2, is used. Heating System
Several types of heater have been used-large gas burners, open seam “stoves,” and internal and external electric heaters. Open flames are objectionable, and when the liquid is a low-boiling solvent the steam stove is preferable. It is shown in T , Figure 1, formed of 40-ounce copper. Steam introduced in theupper tube, V , condenses on the under surface of the flask. C o n d e n s a t e d i s c h a r g e s through the lower tube, U . The usual objectionable leak of steam around the pan is prevented by covering the top bead of the pot with a piece of rubber tubing split throughout its length and allowing the flask to rest on this as a gasket. An electric stove with a capacity of 2 kilowatts has also been constructed and used with the flask Reducer superimposed above bare resistance Figure 2-Doub1e-F1anged wires. It is only slightly preferable to the gas flame from a safety standpoint and, like it and the steam stove, has the disadvantage of the thermal resistance and lag through the heavy glass bottom of the flask. By far the best type of heater is the helicoil sheath unit supplied by the General Electric Company. This consists of copper tubes 10 mm. in diameter by 1500 mm. long with nichrome heating elements inserted and insulated from the sheath in the middle 1000 mm. of the length. The 250 mm. on each end carry the lead wire only, since the ends are not immersed. These heaters are wound in coils small enough to allow insertion in the neck of the flask and each consists of three turns and the two leads. I n a stoppered flask the leads
r-I
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are brought through holes in the stopper and, rvith the connection piece of Figure 2 , the two ends are held apart by an H-shaped spacer of glass tubing, and the barelead )vires are drawn through the side tubes. One or two of thebe heaters, rated at 2 kilowatts each, are used and this amount of heat as a maximum may be delivered nithout loss to the boiling mixture in the still pot. Besides efficiency and s a f e t y , t h e principal ad1 antage of this type of heater is its adaptability for use with a thermostatic system because of the instantaneous reqponce in the rate of boiling t o a slight change in the e. m. F. supplied. The pressure-regulating system is used tlxactly as previously described (4) except that the relay is arranged to make vontact and thus short-circuit part of the rheostat on the break of the primary (manometer) circuit rather than on the make as formerly. The m a n o m e t e r cnontact and the attendant small spark we on the low or atmospheric side rather than on the high or vapor side, which n-ould be dangerous with inflammable vapors and air in the manometer tubing. A sensitive pressure regulation is essential, since the pressure in the still pot is very small, especially while using the packed columns, and the change of the sti’l-pot pressure by 1 mm. of mercury makes a large change in the rate of disC m. tillation. The pressure lea, TV in Figure Uure 3-Bubb1e C o l u m n Cap 1, of the manometer is large compared with the other, and practically all of the mercury movement is on the atmospheric side. This side is of 3-mm. tubing and a t an angle of about 10 degrees with the horizontal, so that a small difference of mercury level magnifies the movement along the tube. Contact is made by a piece of platinum-tipped nickel wire, which may be held at any desired point by the binding-post screw, 2. The permanent contact is through the wire, Y , connected to a tungsten wire insealed through the Pyrex glass. Changes in operating pressures are made by adjusting the sliding contact or adding mercury through the stoppered neck, X.
been given between 15 and 25 ciii. In practice the packed columns have been found to agree well with these results. The product produced in the 5-cm. (2-inch) packed unit varies from 1 to 5 liters per hour depending on the liquids handled and the amount of rectification required. The 7.G-cm. ( 3 - i n c h ) column ha? over double the capacity of the 5-ern. column 011 the same separation. The plate column has a somevhat higher efficiency per plate than a plant-size unit and has about the same
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IJses and R e s u l t s
As indicated above, the distillation equipment described has been used for small manufacturing and experimental purposes. It has proved very adaptable for the preparation of any quantity up to several hundreds of liters of many liquids manufactured or purified by distillation processes. It has also made practical the study and development of distillation projects on a small scale. Because of the flexibility of the various units, many processes involving several different but interconnected columns have been operated successfully, either in miniature for the study of existing plants or on a preliminary scale destined t o be projected to plant operations. Much can be learned from such small glass systems and time and expense saved in development work where formerly it was thought impossible to duplicate plant distillation processes and efficiency in the laboratory. The efficiency of a column packed with glass Raschig rings has been determined by several investigators under varying conditions and the height of packed space which is equivalent to a perfect “equilibrium unit” or “theoretical plate’’ has
Figure 4-Dephlegmator
a n d Condenser
capacity as a packed column of the same diameter. Tests on the relative efficiency and capacit’y of these units will be published at an early date. L i t e r a t u r e Cited (1) ?ruun, 1x0. ENG.CHEM.,Anal. E d . , 1, 212 (1929). (2) Clarke and R a h r s , IND.E N G . CHEX, 18, 1092 (1926). (3) Hausbrand, “Principles and Practice of Industrial Distillation,” p. 32, Wiley, 1928. (4) Othmer, IKD. ENG.CHEM.,Anal. E d . , 1, 97 (1929). ( 5 ) Othmer, I b i d . , 1, 153 (1929).
Disposal of Condemned Ether-How to dispose of 1300 cases of ether condemned under the food and drugs act as unfit for use gave the authorities in a Middle West city cause for thought recently. The fire hazard precluded putting so much inflammable material down the sewers or pouring it out on the city dump. Accordingly, the cans of illegal ether were emptied over the snow in a waste place, where the volatile liquid soon evaporated with no injury to life or property.
