JUNE, 1951
0
AN IMPROVED MELTING POINT APPARATUS 1. E. NICKELS Koppers Company, Inc., Mellon Institute, Pittsburgh 13, Pennsylvania
AN IMPROVED form of the Hershherg precision melting point apparatus1 that has given very satisfactory service for five years is described herein. Several advantages of the improved melting point apparatus are evident from the figure. The doublewalled construction of the thermometer well minimizes possible temperature surges. The Anschutz thermometer rests on the bottom of the well and is automatically centered, leaving ample space for several melting point tubes. Use of square tubing (Fischer and Porter Company, Hatboro, Pennsylvania) for the themowell leg of the apparatus permits better ohservation by avoidmg optical distortion effects. A helical stirrer rotated in a close-fitting collar gives positive circulation of the heat transfer medium. External electrical heating makes possible the use of various heattransfer media, either electrolytes or nonelect~olybe~. Silicone fluid (Dow-Corning, Type 550, 112 centistokes viscosity at 25'C.) was found to be very satisfactory. The tubular helical coil within the heating leg permits rapid cooling with a stream of air, and it may also be used for cooling the heat transfer fluid for low temperature operation by circulating rt cooling medium through it. The heating element comprises about 13 feet of No. 28 B. and S. gage resistance wire (4.07 ohms per foot) wrapped as a noninductive winding on the heating leg with the middle of the wire looped around the lower anchor and the two ends attached to the upper wire anchors. The individual turns are separated by ashestos cord and the whole is insulated with asbestos cloth tape. The heat input is controlled by means of an autotransformer, adjustable from 0 to 135 volts. I m p r o d Melting Point Apparatu. Suitable melting point tubes (ca. 8 inches long) are readily prepared from commercial thin-walled capillary tubine of 1.5-2.0 mm. diameter (Kimhle Glass. Toledo. HERSHBERG, E. B.,Ind. Eng. Chern., Anal. Ed., 8,312(1936). Ohio).
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