Constant-Level Feeder for Thermostatic Baths and Continuous Evaporators M.S. TELANG, Laxminarayan Institute of Technology,
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ARIOUS forms of useful constant-level devices for thermostatic baths a t elevated temperatures have been described (2-14, 16-23). Such devices may be broadly classified into three groups: (1) The common form of constant-level attachment not employing the siphon principle, but working in combination with an overflow arrangement. To attach this form t o the bath, it is necessary to drill a hole in the bath. (2) Devices depending upon the siphon principle in combination with an overflow arrangement, requiring no drilling of hole to attach to the bath. (3) Devices using siphon system in accordance with the principle of the bfariotte bottle, eliminating drilling of any hole in the bath vessel. Objections to the first type have been pointed out by Wilde (30). Devices of the second type have certain advantages, but require a thermostat in a place easily accessible to a water tap and drain. They waste water, sometimes even hot water, and for this reason, they consume more of the gas or electricity used for heating in conjunction with thermoregulators. If the tab water is not soft enough, these devices cannot be run with distilled water to avoid scale formation in the bath. Some of these devices involve a lot of glass blowing. I n many cases, it is neces3ary to pay periodic attention to adjustment of water flow. The third type eliminates the defects of the first two types; however, reservoirs must be frequently refilled, though attempts have been made by some authors to minimize refilling. The present paper deals with the third type, simplifies the construction of older forms, indicates improvements over previous forms, and discusses both advantages and disadvantages. The device is shown in Figure 1. Clamps and other supports are not shown in the diagram.
A serves as the water reservoir, D being the refiller. *is I’ the feeder to the bath, G , being flexible, permits adjustment of levcl L in M . The splash head, H , prevents carrying over water from .M back into A : The limb, HZJ, can be regarded as a balancer of pressure in A and consequently as a level controller in M . Funnel J is necessary, as otherwise, even if the level falls below L, a column of water remains suspended in I , owing to surface tension effects, and will throw the feeder out of action. To start working, the lower end of N is immersed well below level L which, in turn, is adjusted to e, predetermined height by the position of the rim of J . P is closed and A is filled with water through D. While fillin A , P should be closed, as otherwise the water level in M rises a%ove L by draining through N . Extra pressure produced by compression of air enclosed in the space above the water leveli n A during filling through D will be relieved by the escape of air bubbles through F and ultimately through J . If filling of A is stopped by closing the t a p of D and if P is then opened, a slight readjustment of the levels of water in both A and M takes place and water rises in tube Z until it is the same as in A as shown a t B. If the water is cold a t first, the level in M stands afraction of a centimeter above L. As heating and evaporation progress, the level falls to L and remains practically constant throughout. Whenever the level falls very sli htly below L owing to continued evaporation, the water seal at t%e rim of J is broken and air bubbles escape into A through HZJ. The pressure of air enclosed above water in A thus increases slightly, thereby driving more water through feeder N until the level in M rises again t o L and reaches the mouth of J . This process continues as long as there is a water head available in A . When the water becomes hot, the water in the balancer may rise a little higher than in A , owing t o diminution in density of water a t elevated temperatures. Operation is an application of the principle of the Mariotte bottle. The flow of water from A depends jointly upon the head of water and the pressure of air enclosed in A , Since the pressure of air in A is controlled by the balancer limb, H I J , it is evident why the flow of water from A into &. should I stop when the mouth of J is sealed by water reaching level L. The above arrangement is a modification of Gerdel’s device (Y), which has the following defects: To refill, the stopper of the reservoir bottle must be removed or a separatory funnel attached through the stopper by boring a fourth hole in it; this leads t o an undesirable state of congestion. Siphoning continues during refilling if done through a separatory funnel, and thus raises the level of water in the bath. At the boiling temperature, some water is carried from the bath back into the reservoir, owing to the increased frequency of air bubbles rising in the balancer limb. This may not be a serious defect so far as the thermostatic bath is concerned, but if all the distilled water in the reservoir is not used up by the bath, the water remaining mill be rendered unfit for other purposes, owing to contamination nith the water in the bath. At elevated temperatures, air dissolved in water is expelled and air bubbles accumulate a t the head of the siphon, hindering or stopping the siphoning operation. These defects are eliminated in the improved device here described. The advantages of this arrangement are obvious. It can be made of materials readily available in a good laboratory. It feeds water to the bath only when necessary, eliminating wastage of hot water. It can be set up in any desired place. It avoids any damage to vessels, especially those of glass or stoneware. It can be worked even a t the boiling temperature. rlny desired water level in the bath can be obtained quickly by adjusting the position of the rim of J. The device and the bath are entirely independent of each other, hence substitution of either is possible. As there is no continuous flow of water, adjustment of flow needs no attention. Dissolved air expelled from hot water in the bath has no place to accumulate to obstruct siphoning operation, as the flow of water depends mainly upon the hydrostatic head. There is no complicated glass blowing, as the equipment needed is of standard type. It can be used with any quality of water, being specially suitable for distilled water. Refilling of the aspirator
P
Figure 1.
Nagpur University, Nagpur, India
Constant-Level Feeder
A . Aspirator bottle of any, convenient size. B . Water level at be i n n k B , Water level at end. C. Single-hod rubber stopper to fit bottom D Se araton funnel of tubulature outlet of A any sire. E. Doubl;-hol;d rugber stopper to fit mouth of A. P. Connecting glass tube b m m . diameter. G. Rubber tube. H. Spidh head such as that of Kjeldahl’s apparatus. I . Long stem of funnel J fused or connected b y short rubber tube to H Rim dlameter of J 5 cm diameter of I 6 mm. k. Delivery tube, 3-mm:’diameter. L. Actual level of water in thermostatic bath M coinciding with rim of 1. N. Feed tube of g l k , 3mm. diameter. P. Pinchcock and ahort rubber tube connecting N and K.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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bottle is necessary; but this is not serious if an aspirator bottle of large capacity is chosen. For a thermostatic bath of normal size (IS), refilling may be necessary once a day. If a metal tank reservoir is available, so much the better. CONTINUOUS EVAPORATORS. Evaporators may be of various types (I),but they are either open pans or closed bodies employing vacuum. They may be of the small-scale laboratory size
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If an evaporating basin is substituted for a thermostatic bath, the arrangement in Figure 2 can be readily understood. If a separatory funnel is substituted for an aspirator bottle, the liquid to be evaporated can be completely drained, especially when a measured volume of liquid is placed in it. I n order to accommodate the arrangement properly, the stem of the separatory funnel is bent as shown, and drawn out to a narrow tip of about 3-mm. diameter. Air bubbles that may remain in the stem of the separatory funnel may be expelled by pinching a rubber tube temporarily attached a t the tip. If a rubber connection is undesirable, H and Z may be joined by fusion, as the liquid splashes right up to the splash head, H. The apparatus is simple and easily constructed and can give satisfactory service even in analytical work. LITERATURE CITED
(1) Badger, W. L., “Chemical Engineer’s Handbook”, edited by Perry, p. 1042, New York, McGraw-Hill Book Co., 1941.
Figure 2.
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Feeder for Continuous Evaporator
or the larger size used in industry. The essential features of a laboratory-size continuous open evaporator are described in the present paper; results referring to a vacuum evaporator Till form the subject matter of a future paper. Literature on the subject of constant-level feeders for continuous evaporators, particularly laboratory or pilot-plant size, is rather scanty. *4device for maintaining a constant level during continuous evaporation in the determination of total dissolved solids in water recently described (15) has to be specially made t o given specifications, and so does not permit the choice of materials ordinarily available in a laboratory.
(2) Bencowita, I., and Hotchkiss, H. T., IND. ENG.CHEM.,16, 1193 (1924). (3) Brooks, Richard, J. Chem. Soc., 125,1546 (1924). (4) Eddy, C. W., Chemist-Analyst, 18, 20 (1929). (5) Eimer & Amend, “Modern Laboratory Appliances”, p. 915, Catalog No. 15-526, New York and Pittsburgh, Fisher ScientificCo., 1942. (6) Fouque, G., Bull. SOC. chin., 41, 115-16 (1927). (7) Gerdel, R. W., IND. EXG.CHEM.,19, 50 (1927). (8) Griffiths, R., “Thermostats and Temperature Regulating Instruments”, p. 37, London, C. Griffin & Co., 1943. (9) Holmes, F. E., IND. EXG.CHEM.,AXAL.ED.,12,483-5 (1940). (10) Jefferson, R. E., IXD.ENQ.CHEM.,16, 1230 (1924). (11) Meyer, Lester, Chemist-Analyst, 20, No. 2, 16 (1931). (12) Pocock, B. W., IND.ENG. CHEM., ANAL. ED., 14, 811-12 (1942).. (13) Reilly and Rae, “Physico-Chemical Methods”, Vol. I, p. 185, London, Jlethuen & Co., 1940. (14) Robertson, J. H., J . Chem. Education, 10, 377 (1933). ENG.Camf., AN.~L.ED., (15) Schwarts, >f. c.,and Gayle, F. L., IND. 16, 120 (1944). (16) Stannard, TV.S., Pharm. J., 118,245 (1927). (17) Stehle, R. L., IND. ENG.CHEM.,17,466 (1925). (18) Stehle, R. L., Science, 63,404 (1925). (19) Vinycomb, T. B., and Vogel, A. I., J . Chem. Soc., 1932, 2088. (20) Wilde, H. D., IKD.ENG.CHEM.,16, 904 (1924). (21) Wilson, X. F., and Carleton, R. K., J . Chem. Education, 6 , 1335-6 (1929). (22) Wing, H. J., IND.ENG.CHEM.,17,630 (1925). (23) Yohe, G. R., and Keckler, C. G., J . Chem. Education, 11, 462 (1934).
Adsorption Apparatus without Stopcocks for Use with Hydrocarbon Gases C. B.
WENDELL, JR., G. L. Cabot,
Inc., Boston, Mass.
T
ployed for surface area measurements using nitrogen as the adsorbate.
The Brunauer-Emmett-Teller method has been used in the author’s laboratory for the past five years for determining the surface area of a variety of fine pigments. During this period, a n apparatus which is accurate and reasonably foolproof in operation has been developed. Figure 1 shows the apparatus em-
The apparatus, as originally constructed, was similar to that used by Benton and White ( I ) . It consists of a constant-volume buret with two internal blue glass pointers sealed in the constantvolume arm a t suitable points to provide two volume figures, one approximately twice the other, for versatility in operation. Conventional mercury reservoirs are used to control the mercury levels in buret J and manometer 1. The usual 120” three-way stopcock first used on the gas buret vas unsatisfactory. This particular design of stopcock has such a short distance between each two of the three side arms that it frequently leaks under high vacuum conditions. To overcome this difficulty, stopcock, D (fabricated by Eck and Krebs, Ken, York, N.Y., shown in detail in Figure 2) was employed. This cock has very little dead space in the bore, yet has a full 180”between the two side arms. Figure 2 also shows a special adsorption cell, C, designed to reduce operating time when a series of samples of the same density is to be measured. Since the dead space in this cell remains constant as long as samples of the same
H E development of the Bcunauer, Emmett, and Teller lowtemperature adsorption isotherm method for determining the surface area of finely divided substances (2-7) has led to widespread acceptance and use of this procedure in many laboratories. The validity of the method has been further established by the work of Harkins and Jura (8, 9, IO), whose approach to the problem involves precision calorimetry and makes no sssumption as to the effective cross-sectional area of the adsorbate. Their measurements yield surface area values in excellent agreement with those of the Brunauer-Emmett-Teller method. APPARATUS F O R INERT GASES
