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A CONVENIENT CONSTANT-TEMPERATURE HEATER WESLEY W. WENDLANDT State University of Iowa, Iowa City,Iowa
IN A
RECENT article, a constant-temperature heater using various boiling liquids was presented.' Other types of constant-temperature baths using a liquid medium have been described. A type of constanttemperature heater which does away with the various liquid baths is shown in the figure. This heater was
D, DeKhotinaky therrnoregulstor. A . Absorption tube for iaobaric or isothermal dissociation ovrve study
used to study isobaric and isothermal decomposition curves but could also be useful in heating sealed tubes to any desired temperature up to 300°C.
' TUCKER. 8.H.. J. CHEM. EDUC., 30, 634 (1953).
The device is easily made from very common lahoratory apparatus by anyone with moderate glass-blowing skill. It consists of an L-shaped Pyrex tube of 30 mm. diameter; the vertical section is 16 cm. long and the horizontal section about 19 cm. long. The glass is wrapped with several layers of moistened asbestos paper, and after drying, 30 turns of No. 24 gage nichrome wire is wound a t l/rinch intervals as indicated on each section. With this amount of nichrome wire the resistance of the total winding is about 10-15 ohms. After winding with wire, the tube is covered with several layers of asbestos paper to serve as insulation. The temperature regulation device consists of a DeKhotinsky thermoregulator, held in the vertical arm by a split one-holed rubber stopper. The De Khotinsky regulator is connected in series with the coil windings. The leads from the regulator are connected to a source of variable voltage, such as a commercial Variac. The Variac is necessary to limit the current flowing through the heating coils. At a little above room temperature about 10 volts is needed, while at 300" about 65 volts was found to maintain a temperature of +lo. The device as built has a range of from room temperature to about 300". It is capable, with proper voltage regulation, of maintaining any temperature within this range to about + l o . The convenience of this apparatus was demonstrated when it was used to study isothermal or isobaric decomposition curves between methyl amine and an anhydrous salt. By the use of this device the temverature desired is adjusted bv turning the knob on the DeKhotinsky thermoregulator and adjusting the proper voltage on the variac, rt was found that temperatures could easily he maintained for several weeks while waiting for equilibrium conditions on the decomposition curve.
