A 54,. II-. '98^ 
 
 l^ 
 
 ET-98 May 1937 
 
 United States Department of Agriculture 
 Bureau of Entomology and Plant Quarantine 
 
 A SMALL THERMO-REGULATED WATER BATH HEATER 
 
 By Loyal H. Davis i and E. M. Livingstone, 
 Division of Truck Crop and Garden Insect Investigations 
 
 In the course of experiments on the toxicity of hydrocyanic acid gas 
 to the larva of the cigarette beetle it was necessary to secure accurate control 
 of the temperature in the furaatoria. This was accomplished by means of a con- 
 stant-temperature water bath in which the fumatoria were immersed. 
 
 The heating unit herein described and illustrated does not differ in 
 general principle from those commonly used for maintaining a constant water- 
 bath temperature. It has been compactly and simply constructed, however, and 
 may be built economically in a field laboratory. 
 
 The apparatus is made up of a thermo-regulator. a heater-type electric 
 bulb, and a stirrer operated by a small electric motor. The parts were mounted 
 on a portable framework of wood. The thermo-regulator, purchased from a manu- 
 facturer of scientific instruments for $10, was easily adjusted for any desired 
 temperature. In order to prevent the current from arcking between its contact 
 points a small condenser was attached. The heater-type electric bulb was 
 purchased from a therapeutic supply store and cost approximately SI. A small 
 toy electric motor, costing $1.50, was used to operate the stirrer. This type of 
 motor took up small space, produced so little vibration that the contact points 
 of the thermostat were not affected, and gave a long period of service. The 
 stirrer was made of glass tubing 8 mm. in diameter. One end was connected to the 
 motor drive by means of a short piece of noncollapsible rubber tubing, no 
 screws being used. The end of the stirrer extending into the water was sealed, 
 and for a distance of 1\ inches from the end was flattened and bent propeller- 
 wise in order to produce the stirring effect. As shown in figure 1, the unit 
 was wired so that the stirrer ran continuously while the heater-type bulb op- 
 erated through the thermo-regulator. By the use of this apparatus a constant 
 temperature of 82° F. + 0.25 was maintained in a bath containing 7 gallons of 
 water. 
 
 ^Formerly field aide 
 
Digitized by tine Internet Arcliive 
 
 in 2012 witli funding from 
 
 University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation 
 
 http://archive.org/details/smalltherOOunit 
 
MOTOR' 
 
 STIRRER- 
 
 ^ 
 
 =30flOC= 
 
 -WIRING 
 
 LIGHT BULB 
 
 ^ 
 
 Figure 1 Working diagram of smaU thermo-regulator, top and side 
 
 views, showing construction of heating unit. 
 
 Figure 2.— Outline sketch of therrao-regulated heating unit, showing 
 relative size of bath, motor, stirrer, condenser, and connections. 
 
UNIVERSITY OF FLORIDA 
 
 3 1262 08721 6726 
 
 \