A CONSTANT-TEMPERATURE VAPOR BATH
A CONSTANT-LEVEL WATER BATH FOR THE STUDENT LABORATORY
F. BESSINGER and V. PRETORIUS University of Pretoria, Pretoria, South Africa
JAMES 8. SLAGLE and WESLEY W. WENDLANDT Texas Technological College, Lubbock, Texas
A VERY simple constanttemperature furnace for use in kinetic studies in the gas phase has been developed in this lahoratory. It is compact and can easily he constructed at low cost. Temperature control with this apparatus compares very favorably with the more elaborate electronicallycontrolled electric fnrnaces. The cylindrical reaction vessel A, 40 cm. in diameter and 70 cm. long, is heated by the vapor of a boiline liauid * . laced in a cylindrical vapor jacket B, 60 cm. in&ameter and 150 cm. long. Entry to the reaction vessel is gained by means of a capillary tube. The reaction vessel A contained in vapor chamber B cannot be removed. The vapor is condensed in the external condenser D. This arrangement eliminates the possibility of the reaction vessel coming in contact with the relatively cool condensed vapor: Heating is effected by means of resistance wire E wound around the base of the vapor jacket containing the liquid. Energy input is conveniently controlled by means of a Variac unit. Provision for temperature measurement is provided by the mercury-filled well F into which a thermometer may be inserted. Mercury tends to distill a t a high temperature and is therefore hazardous, but it was found that high-boiling liquids like phthalate esters did not provide efficient contact be-
THEuse of a heated water bathis frequently advocat,ed in the student laboratory. Several devices for preventing the water in the bath from evaporating to dryness on prolonged operation have been described.' However, both of these devices are too complicated for general student use. A simple arrangement which has given good results is shown in the figure. Two one-liter Florence flasks, A and B, filled with water, are inverted over the bath C, as illustrated. When the water in the bath falls below a preset level, air is admitted into the flasks through the connecting tubes, allowing water to enter the bath. To maintain a more even flow of water, the tubes admitting air into the flasks have a 45" bevel cut on the immersed ends. It has been found that this arrangement will hold a constant level in the bath for periods up to 24 hours a t temperatures from ambient t,o the boiling point of water.
Liauid Acetone Methanol Carbon tetrachloride Ethsnal
Normal boilina point
56.loC.
. Wster Chlorobenzene n-Xvlene Pentachloroethane Propylene glycol Ethylene glycol Ethvl benzoate ~ugenol Diethylphthalate
160.5 188.2 197.2 212.0
'ROBERTSON, 3. H., 3. CHEM.EDUC.,10, 377 (1933). G. R. 3. CHEM.EDUC., 11,462 (1934). YOHEA N D C. G. KECKLER,
tweeu the reaction cell and the thermometer. Evaporation of mercury a t high temperature can be minimized by attaching a long air condenser to the well. Low-melting alloys ( e . g., Wood's metal) are not recommended because they expand on cooling. This might cause damage to the well. The apparatus is insulated by asbestos lagging G coated with sodium silicate solution. Liquids are introduced through D and drained through stopcock C. The efficiency of temperature control was tested by using the vapor from water, ethyl benzoate, and eugenol, boiling a t 95.5"C., 205.ZoC., and 245.0°C., respectively, a t 650 mm. Hg pressure. In each case temperature variation was less than O.l°C. Suitable liquids for use with this apparatus are listed in the table.
