A Laboratory Cooling Unit D. H. COOK Department of Chemistry, School of Tropical Medicine, University of Puerto Rico, Columbia University, San Juan, Puerto Rico HE need for an adequate supply of cold water for chemical laboratories located in the tropics or in the southern
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part of the United States is often imperative. Pipes for city water supplies are in general laid close to the surface of the ground and become heated by the sun, and their contents attain temperatures comparable with their environment. A clever device for cooling a thermostat with cracked ice was reported recently (S), and many have had recourse to the timehonored method of running t a p water through a metal coil immersed in a pail containing ice and water; but a t best these are only makeshifts. The use of refrigerating units for the laboratory is not new. Foote and Akerlof (2) have modified such a unit for thermostat control below room temperatures but the method as worked out in this laboratory does not seem to have been described before.
CONSTRUCTION OF COOLING UNIT A small Frigidaire unit, model S, was modified as follows: Castors were mounted on the four short legs of the compressor frame and a handle was attached to one end of the frame. Four 17-inch steel rods were bolted to the corners of the frame in a vertical position, to support a wooden box of 0.5-inch stock, 22 inches long, 17 inches wide, and 20 inches deep, outside dimensions. This box was approximately the size of the frame of the unit, and was mounted above the compressor, clearing it by about 2 inches. A tank of heavy galvanized sheet iron, 15 inches long, 14 inches deep, and 11 inches wide, constructed to serve as a reservoir for the cooled water, was mounted in the wooden box and given a 2-inch clearance at the bottom by being supported on four wooden blocks. The expansion tank and cooling coil assembly of the Frigidaire unit was suspended in this galvanized iron tank, being supported by strap iron hangers from the rim with about 1-inch clearance between the cooling coils and the bottom of the water t m k . The pipes from the compressor were led up through one corner of the wooden box and through a hole drilled in the wall of the water tank a t a point about 2 inches below the rim. This allowed them to make their normal connection with the expansion tank at a slight slant so that any condensed gas could drain back to the compressor reservoir. The air space between the walls of the wooden box and the metal water tank was insulated by packing withsawdust, and the last few inches near the top of the tank, above the water level, was tamped with newspaper. Two 0.385-inch copper pipes were introduced a t one end of the assembly by drilling two holes, 9.5 inches apart, through the box and the iron tank, 2 inches below the rim of the tank. One pipe, to serve as the suction end for the pump, was bent at a right angle after entering the tank so that the end was about 0.5 inch from the bottom and would draw water from the coldest layer. The other pipe, for discharge, was continued on through the water tank to within an inch of the opposite wall and its tip bent down slightly, so the returning water would not splash and would help to maintain a good circulation around the cooling coils. The tank and all exposed metal parts were given a heavy coat of aluminum paint to prevent corrosion, or could be made of heavy sheet copper if the unit is to be placed in daily service. A hinged wooden cover, with 1.5-inch wooden batten that fitted the top of the water tank, completed this part of the assembly. Outside the box, on a shelf below the two copper pipes, a small rotary water pump was mounted. A 0.1-horsepower synchronous motor from the laboratory was screwed to the other end of the shelf and belted to the ump. A snap switch mounted in the motor line completed %is detail. Pump connections to the copper pipes and to any apparatus were made with rubber tubing. A fuse block and double-pole single-throw switch mounted on the bottom of the wooden box safeguarded the com ressor motor. A flexible lead attached ahead of this main line switc! and brought u to the pump motor made the water circulation independent the operation of the cooling unit. Ten feet of heavy-duty lamp cord, running from the fuse block and with plug attached,
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allowed the unit to be moved to any situation in the building and plugged into the nearest outlet.
OPERATINGDATA Operating data on a n apparatus of this type are only relative, since the efficiency is affected by room temperature, air movement, etc., while the total volume of water to be cooled, insulation of the tank, adequate stirring, etc., affect the rate of cooling. T h e capacity of the w a t e r tank is a b o u t 24 l i t e r s , f bringing the water level a little above the base of the expansion c h a m b e r and assuring goo d contact with all the c o o l i n g assembly. With the pump operating at about 750r. p.m.,3.5liters per minute of cooled water can be circulated through a Bailey-Walker extractor or through an o r d i n a r y glass condenser. W i t h closed a p p a r a t u s t h e d i s c h a r g e is under pressure from the pump and theref o r e the condenser or other apparatus can be located above or below the water level in the cooling t a n k . With connections open to the air, the d i s c h a r g e has to drain back to the tank by gravity and this fact should be kept in mind in designing the unit. FIGURE1. CROSSSECTION OF Box AND COOLING TANK A supplementary d i s c h a r g e pipe of 0.5-inch diameter may also be necessary where the flow is under a head of only 2 or 3 inches, in order to prevent backing up. The use of a direct current motor with variable-speed control for changing the rate of pumping might be of advantage. A convenience well worth installing is a 0.5-inch T connection soldered to the discharge pipe with the T inverted. A thermometer mounted in this vertical opening by means of a rubber stopper with the bulb projecting into the current of discharged water will give the temperature of the returned water and will indicate when the unit needs to be started or stopped. I n the normal operating range from 12" to 20" C. the unit
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ANALYTICAL EDITION
will give the hourly equivalent of the melting of 4.8 kilograms of ice, Inactual practice, circulating water through a BaileyWalker 6-unit extractor, using ether, and with no precautions to prevent radiation from the hot plate being absorbed by the water line, it was found possible to maintain the discharge water a t a temperature from 16" to 20" C. by operating the compressor for 40 minutes and shutting it, off for 30, while, if the temperature of the discharge was held between 18" and 24" C., 30 minutes' operation with one hour idle was possible. This intermittent operation could easily be made semi-automatic by introducing an interval timer and mercury contact relay in the power line of the compressor. With better insulation and some other liquid than water, temperatures of 0" C. or below might easily be attained. Though sawdust is not the best insulating material, the gain of heat from the outside is on the average 18 Calories per hour when the room temperature is from 25" to 28" C. and the tank temperature above 12' C. At lower temperatures the heat loss becomes greater. When cooled to 2" C., the tank water rose 3.6" in 3 hours, or an average gain of 28.8 Calories per hour. With the tank water cooled to 6" or 8" C. a very short condenser serves efficiently, even with low boiling point petroleum ether. With longer condensers and this low-temperature cooling, high distillation rates can be maintained without loss, and i t often becomes unnecessary to pack the receiver with ice. I n humid climates condensation of water from the air may become a nuisance, but the wrapping of exposed parts with insulating material will obviate this to a large extent.
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By circulating cooled water through a few coils of copper tubing immersed in a thermostat, the temperature of the latter may be maintained s!ightly below the regulating point, so that electric heating of the bath for regulation can be used as in colder climates. This unit has also been found of service in photographic work. By the use of water-jacketed trays for developing, washing, and hypoing, the trays and their contents may be kept a t any desired temperature. The cooling unit can be kept outside the dark room and the cooled water pumped through two pipes passing through the wall and connected with the jacketed trays. A switch located in the dark room and controlling the current in the compressor motor line gives adequate control of the temperature. Cooling machines (1) for commercial photographers are already on the market, but are too expensive for most institutions with only irregular demands on the dark room.
ACKNOWLEDGMENT The author wishes to express his appreciation to Mr. Casafia for aid in assembling the unit and making various constructional details. LITERATURE CITED (1) Crabtree, J. I., Am. J. Phot., 16, 462 (1932). (2) Foote and Akerlof, IND.ENQ.CHEM.,Anal. Ed., 3, 389 (1931). (3) Stier, Science, 73, 288-9 (1931). R E C E I V ~November D 29, 1932.
An Inexpensive Muencke Blower RICHARD F. ROBEY, Chemical Laboratory, The Ohio State University, Columbus, Ohio
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CURRENT of air of sufficient pressure to operate a blast lamp or a stirrer for the laboratory where the expense of a mechanical compressor is prohibitive can be obtained from a simple Muencke type of blower constructed from a varnish can and a few pieces of galvanized iron pipe and fittings together with an aspirator pump, as shown in the accompanying cross-sectional diagram.
FIGURE 1. DIAGRAM OF BLOWER
-4hole, just large enough to admit the nipple G, and a slit, upward from the hole, long enough so that the metal may be turned back to admit the elbow E, is cut in the side of the metal container I . The elbow and the nipple, connected,
are then inserted, and the metal that has been turned back is pushed together. The slit and any space around the connecting nipple G are then closed tightly with solder. The soldering, with the aid of zinc chloride paste flux, is extremely easy because an ordinary can is already tinned. The remainder of the fitting is easily done and should be so arranged that the reverse elbow H is not more than one-half as high as the container. A Boekel or straight aspirator pump A can be easily inserted, together with the air outlet tube B which may be made of glass or copper tubing, into a two-hole rubber stopper C in the mouth of the can. The can should be set up a t the edge of a sink, where drainage from the water outlet J and the nail hole F i n the bottom of the can may be permitted. A piece of rubber tubing D, attached to the stem of the aspirator pump, decreases the splashing. Rubber stoppers with large holes may be inserted in the water outlet pipe J to adjust the water outlet flow. The inside diameter of the water outlet pipe should be at least twice that of the aspirator pump. An aspirator pump with 0.95-cm. (0.38-inch) iron pipe threads therefore requires a 1.9-cm. (0.75-inch) water outlet pipe a t full main water pressure. A large bottle connected between the air outlet B and its point of use will aid in giving a steadier pressure, The possibility of better design and method of construction of the blower are obvious, the above being merely a description of a blower which was improvised rather incidentally, but which has been in service for several years. RBO~ZVB November D 4, 1932.
