CONVENIENT, INEXPENSIVE CONSTANT-TEMPERATURE BATH RALPH E. DUNBAR Dakota Weskyan University, Mitchell, South Dakota
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NY STUDENT or instructor with average me- securely soldering these frames to openings in correchanical ability can easily construct a convenient, sponding positions in the two walls of the container. A inexpensive constant-temperature bath similar to waterproof cement for fitting the glass into these the one that we have had in use for nearly three years. frames is easily prepared by mixing dry precipitated The materials required for this piece of equipment are calcium carbonate (whiting) with heavy white lead relatively inexpensive and are often readily available paint until a paste of about the consistency of good in even the smallest and most meagerly equipped labora- putty is obtained. tory. It is with the hope that this information may be A satisfactory stirring mechanism is provided by helpful to others that it is submitted. soldering suitable vanes to a bronze rod J. A series of The constant temperature bath A is constructed of three pulleys L provides for variable stirrer speeds. two cylindrical galvanized iron containers, one placed An additional bearing K soldered to the bottom of the within the other. These containers can easily be container A will give a more rugged construction and fashioned a t small cost by a local tinsmith. The two quieter operation. The stirrer is driven by any small sections should be of such a size that when the smaller is motor M. Two small pulleys N serve to direct the introduced into the larger there will be an open space of belt between the motor M and stirrer pulleys L. The pulleys at N may be raised or lowered by adjusting the position of the crankshaft-shaped rod with the screw in the clamp holder as illustrated. Similarly the two pulleys a t N may be moved nearer or farther apart on this bearing by collar adjustments on either side of the pulleys. This arrangement permits a perfect alignment of the belt with any of the three pulleys a t L and thus affords a t least three distinct speeds with the stirrer J . The heatmg element B may be a large carbon bulb or electric heating element. Even a relatively large 110volt light bulb may be used when the temperature within the bath is maintained only a few degrees above room temperature. The socket C is held in position with an ordinary buret clamp. The thermoregulator in this case has been fashioned F I G ~ 1.--GENER.~. E A ~ ~ ~ N G E Kor E NBATH T from the inner tube of a broken Victor Meyer apparatus for vapor density determinations. One bend in the approximately one inch between the two walls on all lower end of the piece of equipment, just above the sides, including the bottom. This opening should be bulb D, materially shortens the total length. The packed with good insulating material such as cork, side-arm is bent upward as illustrated, t.erminatmg in asbestos, or magnesia. The opening around the top an open end a t G. A small platinum wire, supported by can easily be sealed with a suitable wax or cement, leading it through a small cork G, is introduced for or better yet, closed with a ring of galvanized iron of about two or three inches into the upper end of this suitable size and shape, M y soldered in place. capillary tube. A snugly fitting plunger made of Even a combination of sweeping-compound and large cork or rubber is fastened to a long metal screw as illuslard cans might be improvised for such a container trated a t F. This is introduced into the larger arm. where finances will permit nothing better. A five- An ordinary one-hole cork will serve to lower or raise or ten-gallon cylindrical jar will serve such a purpose the plunger by turning to the right or left. It should quite well, especially if carefully wrapped with "balsam be mentioned that it is absolutely necessary to have a wool," or similar insulating material on the outer side. good metallic contact below the plunger and a conIf a metal is used, the inside surface should be carefully tinuous electrical circuit through to the leads above for protected with two or three good coats of white lead or the six-volt current. The large bulb D may be filled similar paint. A double glass window can easily be with toluene or other liquid with a relatively high coprovided on the side, for observing experimental work efficient of expansion. Mercury E should be added withm, by preparing two metal frames for glass, and from the end of this bulb D to the two contact points a t 627
the upper end. Buret clamps for suppotimg the thermoregulator or chemical equipment may be attached to upright rods H fastened to the wall of the constant-temperature bath. The electrical control board is illustrated in Figure 2. It may be mounted a t any convenient place near the
blade or wall switches, placed as illustrated, will enable the operator to control any of the circuits without affecting any of the others. Figure 3 shows a typical constant temperature bath of this type. Temperature adjustments are made by lowering or raising the plunger in the thermoregulator with the screw a t F. The glass window, which was sealed as meviously described,has not developed a single FIGURE3.-Tns COMPLETED leak after three Bani of nearly constant use. The temperature can easily be controlled within *0.2°C. when operating a t 25' to 30°C. The cost of this constant-temperature bath will naturally vary, depending upon the amount of equipment already available and the amount that must be purchased specifically for this purpose. Likewise variations in size and coustructiou will influence costs, as well as the ability of the operator to construct the various pieces himself, rather than hiring someone else to prepare them. However, in any case, the cost in time and money will be small in comparison to the service received.
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constant-temperature bath. The wiring diagram is practically self-explanatory. Only one lead of heavy extension cord is required for the incoming 110volt alternating current. Two short lengths of similar extension cord lead to the motor M and heating element B. An ordinary six-volt bell-ringing transformer will easily supply adequate current for the control circuit leading to F through the telegraph relay. Four knife-
