High Efficiency Still for Pure Water ROBERT BALLENTINE McCollum-Pratt Institute, The Johns Hopkins University, Baltimore 78,
N THE course of the investigations in this laboratory into the
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the flow have all been tried with uniform lack of success. They do not maintain their setting and this results in failure of the automatic operation. The capillary hm worked without attention for over a year. The boiler, H , consists of a 4000-nil. borosilicate glass resin reaction kettle S o . 6947. I n addition to the clamp ring holding the top in place, a neoprene gasket is essential. It is greased with high-vacuum Dow-Corning silicone stopcock grease. The overflow from the boiler goes to drain via the capillary tube, I . Again a capillary has proved the most dependable flow regulator. although periodic removal of scale is necessary. The heating element proper, J , consists of a spiral of S o . 18 gage Nichrome wire. The wire is 20.5 feet long, with a direct-current resistance of 9.0 ohms. The coil is formed by winding around a broom handle. It is 16 inches long by 1.25 inches in diameter. Brass 1/8-inch welding rods. split a t the end, are attached to the Xichrome b y cinching or d v e r soldering. The other ends of the rods pas.? through rubber stoppers and are threaded so that they may be connected by lug terminals to the power source. I n the still in this lahoratory the voltage a t this point is only 94 volts alternating current, owing to losses in the conduit.^. The still hence consumes 080 watts of poiver. The steam on leaving the hoiler 1) es into a %foot Vigreus column, IC, approximatel>- 2.5 em. in diameter. and equipped with 24/40 joints. Connection between the top of the column and the condenser, C, is by means of a tube. L . slanted so that any condensate is returned to the boiler. I t is further heated by a 2-foot Glas-Col heating tape n.rapped about it. The temperature is maintained a t 120" to 130" C., so as to prevent any continuous water film between the boiler and the produrt condensers. Initial adjustment is carried out as follow. The boiler is filled with water, and the current is turned on to bring it to a boil. Khen steam is issuing from the condensers, cooling water is .started through both of them. The riinchcock is then adjusted to give a maximum temperature in F . After a short period of operation, the rate of product output anti the amount of overflow from I 0 are both measured. A The length of the capillary between F a n d G is then shortened or lengthened so that the overflow is one third of the volume of product per unit time. A short length of plastic t u b i n g facilitates making this adjustment. Caution! Before disconnecting the capillary from the boiler, be sure it has cooled below the boiling point, since the boiler is superheated with respect to the atmosphere pressure. F i n a I 1 y when the adjustment is complete, the c a p i l l a r y , I , may be cut to permit c o n t i n u o u s ejection of slugs of steam and water, but should be kept sufficiently long to prevent a serious Figure 1. Distilling Apparatus loss of steam.
I role of trace elements in plant growth and metabolism, the
need arose for considerable quantities of metal-free water. Conventional stills for the production of triple glass-distilled water did not t'urn out enough m t e r of the desired purity, and required constant attention. The still of Holmes ( 2 ) suggested the design for a continuous flow system which is both highly efficient and semiautomatic. The only primary sources of contamination with metal ions of the product is from the feed waters and the condensing surfaces. The latter source may be made small by careful cleaning and aging of the condensation surfaces, and by maintaining them a t a minimum area, as is done by Holmes ( 2 ) . Cont,amination with metal ions of the product by the feed water must arise from tr:mport by droplets in the vapor stream and/or by creepage along the glass surfaces. The first of these sources is eliminated or reduced to a very small fraction by the employment of a 5-foot Vigreux column as a spray trap. The second source of contamination is prevented by plaring a hot-spot in the vapor path. Whrn thc still head is heated considerably above the boiling point,, no condensation occurs and any film is broken. Therefore, if isolation of the product from these tlvo sources of contamination is achieved, .-everal advantages will be gained for the simplification of the operational characteristics of the still. For example. there is no need to consider the level of contamination of the feed water. This allows freedom of choice in construction materials for the boiler and heater, allowing direct metal immersion heating with its high efficiency of heat transfer and smooth ebulation characteristics. ConFequently, without sacrifice of ease of semiautomatic operation, one may expect to obtain pure water by a single-stage distillation directly from the city main. The following still incorporates these operational features, shon-ing a purification factor of 107 for metal ions, a thermal efficiency of 92%, and an output of a t least 1.5 liters per hour. DESCRIPTIO1 AND OPERATION
Figure 1 is a diagram of the still. Because stable operation of the still requires a steady and reproducible balance of flow rates, the input water flow must be regulated. This is achieved by the constant-head device, A , set to give a 10-inch positive head of water, independent of variations in the pressure of the mains. After leaving the constant-head device a t a rate controlled by the pinch clamp, the feed n-ater is mixed in the chamber, B , with any desired reagents, such as alkaline permanganate or dilute acid When water free of trace metals alone is desired, this unit may be omitted. The heat exchanger, C, is a stock Ful-Jac condenser, 30 em. long, fitted with T 24/40 joints (Scientific Glass Apparatus Co., Inc., KO.5-932-3) To achieve full efficency of condensation, increasing the yield nearly 40%, an identical auviliary condenser, D, is cascaded on the output, and cooled by direct connection to the water mains. If minimum surface of condensation is more important than maximum output of product, this unit may be omitted. The cooling water from C, nearly a t the boiling point, enters the gas disentrainment tube, E, nhich is 10 to 12 mm. in diameter. It is open a t the upper end to the atmosphere. The heated feed water then enters a second constant-head device, F , where any excess is permitted to flow off to the drain, because in operation more cooling water is required than can be directly fed into the boiler. The unit, F , connects t o the boiler, H , by means of a length of capillary tubing of 1.5-mm. bore terminating in the sight glass, G, which permits a ready check on the rate of flow into the boiler. A positive head of at least 44 inches is required, as in operation there is a positive steam pressure of 30 to 40 inches within the boiler. This capillary is utilized to control the flow rate, being shortened or lengthened as necessary during the initial installation. Pinch clamps, stopcocks, and other methods of regulating
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ANALYTICAL CHEMISTRY
S50 After the unit is adjusted initially, it usually requires no further attention. Each day’s start-up consists simply in brin@n the boiler to a boil sufficiently long to bring the cooling water in to a boil. Then the flow of cooling water is started. A second pinch clamp may be used so the flow setting is not disturbed from day to day. The still in this laboratory operating a t 980 watts puts out 1.45 liters of water per hour. When starting up initially or after a long shut-down, the author operates the still for a t least a day, discarding the product, without cooling water in condenser D so as to leach the glass condensing surfaces.
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RESULTS
Efficiency. While i t is desirable to obtain as high an efficiency as possible, this is true only within the limits that the construction of the still should be kept as simple as possible. Therefore, no lagging of the boiler or any other part of the apparatus was employed. However, by utilizing the heat of condensation in the heat exchanger, this heat can be conserved by bringing the feed water from the temperature of the water mains to nearly the boiling point. In a calibration run the still was consuming 980 watts of electrical power. If this heat were used solely t o ~+uppIyheat of vaporization of water a t its boiling point, then the theoretical product output of the still would be 1.56 liters of water per hour. The measured rate of product output was 1.45 liters per hour, giving a power efficiency of 92.9%. This figure was sufficiently high that no further attempts were made to increase it. Purity. Early in t!ie development of the still a sample was compared to a sample of glass-distilled conductivity water. The conductance values for the air-equilibrated samples were identical. In the past the author has also utilized the dithizone (3) test for freedom from metal ions. While this test gives a positive level of contamination in the products of conventional triple distillation, no such positive test could be obtained with the product of the described still. Indeed, even when the feed water was contaminated with 1000 p.p.m. of copper as the sulfate, the tests for metal contamination were still negative. Therefore, a more sensitive test was required. To this end the boiler containing 3.5 liters of water was contaminated with 5.2 y of cobalt chloride containing 3.2 X 108 counts per minute of cobalt80. Three liters of product were collected, nonradioactive car-
rier cobalt was added, and the cobalt was recovered and assayed for radioactivity ( I ) . Only 41 counts above background were found. This is a purification of 10’ over the feed water, and represents a contamination of 1 part in of the product water with cobalt ion. Frequently one requires water not only free of metal ions, but also of other contaminants, such a? phenols and ammonia. As a test of the system, the feed water was deliberately contaminated with 1000 p.p.m. of phenol and ammonium chloride by means of injection from a motor-driven syringe into the feed water entering the heat exchanger. The reagent addition unit, B, was employed to mix with the feed water a solution of 0.5N with respect to both potassium permanganate and sulfuric acid to act as trapping agents. The feed rate of these reagents was 50 ml. per hour (water feed, 4.22 liters per hour). Visual observation indicated that all of the permanganate Oxidation occurred in the heat exchanger. The ammonia present in the feed water was determined by Kessler’s reagent, and in control tests was sensitive to better than 1 p.p,m. The test on the product was negative. Phenol was tested for by a modification of the method of Vorce (4, 6), which was also determined to be sensitive to 1 p.p.m This test on the product was also negative. Inasmuch as this type of purity was not the main concern, no further development nor extension of these tests was carried on. However, it appears that this still, perhaps with slight modification, is capable of producing efficiently large amounts of metal-free mater which is also free of the other major types of contamination. The still is self-sterilizing and hence should provide an excellent source of pyrogen-free water. LITERATURE CITED
(1) Ballentine, R., and Burford, D., unpublished manuscript. (2) Holmes, F. E., ANAL.CHEX.,21, 1286 (1949). (3) Stout, P. R., and Amon, D. I., A m . J . Botany, 26, 144 (1939). (4) Voroe, L. R., Ind. Eng. Chem., 17, 751 (1925). (5) Yoe, J. H., “Photometric Chemical Analysis, Vol. I, Colorimetry,” p. 429, New York, John Wiley & Sons, 1928. RECEIVED for review April 6, 19.53. Accepted October 13, 1953. Contribution No. 44 from t h e McCollum-Pratt Institute. This work was supported i n part b y a contract, AT(30-1)-933,between the Atomic Energy Commission and t h e Johns Hopkins University.
Detection of Steroidal Pseudosapogenins by Infrared Spectroscopy ALMA L. HAYDEN, PHYLLIS B. SMELTZER, and IRVING SCHEER National lnstitute of Arthritis and Metabolic Diseases, National Institutes of Health, Department o f Health, Education, and W e l f a r e , Bethesda 14, Md.
been reported 3, 4,8, that the spiroketal side chain Ispectrum in steroidal sapogenins has a characteristic infrared absorption in the fingerprint region. This absorption, which is T HAS
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distinctive for sapogenins of the normal and is0 series, is absent in other steroids and in sapogenin derivatives lacking the spiroketal structure. The results obtained in this laboratory from an infrared spectroscopic study of five steroidal pseudosapogenins and some of their 0-acyl derivatives agree in part with this earlier work. I n the present investigation it has been found that the pseudosapogenins (Table I) possess a band of moderate intensity (under the conditions given in the experimental section, the observed absorption is 20 to 50’%) near 1695 cm.-l and do not exhibit strong absorption in the 1000- to SOO-cm.-l region. The absorption near 1695 cm.-l is significant in that it is absent in the original sapogenins, dihydrosapogenins, and products resulting from oxidation or reduction a t the CzO-Cz2 double bond in the pseudosapogenin structure (I). The presence of this band near 1695 cm.-’ and the absence of strong absorption in the 1000- to SOO-cm.-l region may be used as
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means for the detec-
‘ % E d tionof pseudosapogenins. Identification of an individual pseudosapoyenin is made in the usual manner by comparison of its specAtrum with reference spectra. Because the spectra of chloroform solutions of the side chain isomeric pseuHO dosapogenins-e.g., pseudosarsasapoI genin and pseudosmilagenin-are very similar, positive identification can be made most advantageously by comparing the spectra of their Nujol suspensions in the fingerprint region. The compounds were studied in carbon disulfide and chloroform solutions and as Nujol suspensions or liquid smears. The chloroform spectra of the pseudosapogenins are greatly affected by the solvent purity. Commercial chloroform or distilled chloroform which may have undergone partial decomposition on standing can cause rapid transformations (within 12 minutes) of
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