A SIMPLE MELTING-POINT APPARATUS ALEXANDER GERO Hahnemann Medical College, Philadelphia, Pennsylvania
THEmelting-point apparatus described in this paper is distinguished by extreme simplicity of construction and negligible cost. It has been tested by the writer and his students for years and compares most favorably with more elaborate and expensive apparatus. A 25 X 150-mm. Pyrex test tube and a 15 X 85-mm. soft-glass test tube are needed to construct the apparatus. The small test tube is softened in a flame about 2 to 4 cm. from its open end and narrowed t o a diameter of about 2 to 4 mm. It is not a t all necessary t o do this carefully; as will be explained below, the apparatus works better if the narrowing is not accurately centered. The small test tube is now cut off a t the narrow point and its funnelahaped top placed inside the large test tube upside down, i. e., so that the month of the funnel rests on the bottom of the large test tube and the tip of the funnel points upward. Bath fluid is then poured into the large test tube until the fluid level is about 3 cm. above the tip of the funnel, and the test tube is closed with a cork stopper. A hole is bored in the stopper to hold a thermometer, and a sector is cut out in its side for venting and for making the whole scale of the thermometer visible. (See the figure.) A sample of the substance to be tested is placed in a melting-point capillary and attached to the thermometer in the usual way, and the position of the thermometer adjusted so that its entire bulb is just below the surface of the bath fluid. If now a microburner is placed under the test tube, most of its heat will go into that part of the fluid which is inside the inverted funnel. The fluid will therefore expand and rise from the funnel,
quite fast and with considerable turbulence,owing to the narrowness of the opening, especially if the warm fluid rises near the walls of the test tube rather than in the middle. This is the reason why a funnel with a poorly centered tip is preferred. The eddy currents which are thus set up mix the upper part of the bath fluid effectively, no matter whether heating is fast or slow. In all cases the thermometer and the sample are heated evenly, and melting points of excellent reproducibility are obtained.
