A CONSTANT-TEMPERATURE BATH FOR WARM CLIMATES W. M. LOVELESS and MADISON L.
MARSHALL Texas State College for Women, Denton, Texas
CHEMICAL development in the southern states poses a new problem in temperature control. In some areas the maximum daily temperature exceeds 35°C. for days a t a t,ime. For weeks, and sometimes for months, hydrant water may remain above 25°C. The experimenter is forced to make his studies a t temperatures considerably above this or he must resort to some type of refrigeration. Although some buildings are air-conditioned there is a definit,e need for a simple water bath with a cooling arrangement that bas sufficient maneuverability to be easily moved from room to room or from building to huilding. The conventional water bath with cooling coils leadingthrough an ice box or modified refrigerator is sometimes used. Such an arrangement is capable of giving good temperature control but is unduly spaceconsuming and generally difficult to move once it is in operation. The authors designed and built a compact constant-temperature water bath for instructional use in physical chemistry but which has a wider range of application. The bath consists of two tanks, one within the other. The outer tank is 40 in. long., 18 in. wide, and 16 in. deep. It is filled with water which serves as a refrigerant. I t is made of wood mounted on a wooden frame, supported on castors and lined with stainless steel, and is light enough so that even when filled with water the entire assembly can be moved from place to place in the laboratory. The bath assembly is designed in such a manner that one end of the larger tank is used for precision temperature control while the other end is used for the storage of solutions or for temperature regulation of standard solutions during their preparation. For precision temperature control a Sargent constant-temperature unit is placed in the inner tank (a 20-liter jar) surrounded by the refrigerant. Temperature in this tank is maintained over long periods of time with little attention to within +O.Ol°C. For a period of a few hours the variation is considerably less, varying no more than a few thousandths of a degree. The temperature is detemined by a mercurial thermometer calibrated by the U. 8. Bureau of Standards. The coolerant in the larger tank is warmed by a simple type of immersion heater. The coolerant flows through copper tubes which are attached to the inside walls of the tank, traversing the length of the tank ten times before returning to the compressor. The refrigeration unit is a 1/4-horsepowersize of the type supplied by a
The Constant Temperature Bath
local refrigerator concern and requires 460 watts for operation. Water is circulated by means of a vater pump discharging through a copper tube running the length of the tank, closed at its extremity but perforated with holes along its entire length. Both the heat,er and refrigeration units are cont,rolled by Fenvall expanding type electric thermoregulators. Maximum sensitivity for this type of regulator is list,edas =tO.l°C. Some difficultywas encountered with the above arrangement until relays mere inserted between the thermoregulators and the heater and refrigeration units. A terminal box which eliminates hare wires and provides convenient grouping of switches completes the assembly. For precision measurements at 25°C. the outer bath is maintained a t approximately 20°C., the temperature at which volumetric apparatus is usually calibrated. The temperature of the coolerant is maintained easily at this value with variations of less than +l.O°C. Volume changes in water accompanying temperature changes within these limits are less than those encountered in volumetric procedures in the preparation of solutions.
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