H. B. Powell, E. K. Mellon, Jr., ond D. F. BWOW University of Texas Austin
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A Constant-level Oil-bath Melting Point Apparatus
The accompanying diagram illustrates a convenient and inexpensive modification of the TheileDenis melting point apparatus which requires only a source of compressed air and 110-v ac current. This apparatus can be built for less than $15 (including the price of the light-duty variable transformer) in any laboratory equipped with simple glassblowing tools. Incorporation of a leveling overtlow tube eliminates the small temperature errors which arise from changes in the immersion level of the thermometer due to
Figure 1. a, Leveling-overflow tube (8 mml; b, Slddeorrm t n heoting coil lemds ( 8 mm); s, Compreaod air tube (5 mml; d, Thermometer svpportj e, 2-amp fuse; f, Light-duty variable transformer (Superior Electric Co.1; g, 5-volt lomp; h, Power switch.
changes in the density of the bath medium. Placing the nichrome heating element inside the bath, by means of the s i d e a m , provides relatively fast heat response while still allowing easy disassembly for cleaning or repair. Circulation of the bath medium is accomplished by passing compressed air through the smallbore sidearm tube. By proper air flow adjustment the bath temperature in the area around the thermometer can easily be made homogenous. Use of compressed air as the mixmg agent causes no observable increase in the rate of discoloration of a mineral oil bath medium. The melting point capillary is inserted through a 34-mm hole in the wood or cork thermometer support with its lower end resting against the thermometer bulb. Painting the rear half of the bath black and placing a small lamp to one side of the apparatus greatly increases the visibility of the material in the capillary. I n order to simplify the apparatus, the lamp and transformer may be wired in parallel so that only one power switch is necessary. A melting point apparatus of this type has been in trouble free operation in our laboratory for several months; routine melting point determinations are reprod~lcibleto within 0.1"C. Also, since the thermometer immersion levels is constant, it is possible to calibrate commercial partial immersion thermometers a t the exact level a t which they are to be used in the apparatus. We would like to express our appreciation to Dr. J. J. Lagowski for helpful discussion. Also, we would like to thank the Robert A. Welch Foundation for financial support.
Volume 41, Number 6, June 1964
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