APPARATUS FOR DETERMINING BOILING POINTS AND FREEZING POINTS OF SOLVENTS E. E. CHANDLER Occidental College, L o s Angeles, California
THE drawing shows a simple setup for determining molecular weights by elevation of the boiling point and depression of the freezing point of the solvent. The main error in boiling-point methods is due to overheating and a consequent unstable mercury column. This is avoided in the McCoy apparatus by boiling the
solution with the vapor of the pure solvent, which also acts as a jacket to prevent the solution from losing heat to the atmosphere. Over-heating is minimized in the Cottrell percolator method by having bubbles in the solvent or solution burst over the bulb of the thermometer. In this apparatus the solution is in a large test-tube about a foot long. Inside this is a glass tube open a t both ends, and inside this tube is the thermometer, which should reach to the level of the liquid. The test-tube rests on an asbestos wire gauze from which a small amount of asbestos has been removed under the bottom of the test-tube. With a small flame, boiling takes place only in the inner tube. The bubbles of steam rising several inches from the flame to the bulb lose their excess heat, as in the Cottrell method. The annular space between the tubes jackets the thermometer and helps to hold the mercury steady. When the solute is introduced the inner tube may be lifted a few times to insure mixing. This simple apparatus gives quite as good results as the more elaborate apparatus mentioned. No condenser is necessary as the long test-tube partly closed with cotton provides good condensation. In any event the solution may be weighed after the determination, the weight of the solute deducted and the calculation made. The novelty in the freezing-point apparatus consists in a wire basket containing ice, hung to the thermometer by the rubber band surrounding it. Equilibrium is obtained by moving the basket and thermometer up and down in the nested beakers or by so moving the beakers by means of the balance. After the freezing point of the solution has been determined, the basket and thermometer are suspended above the beakers and the weight of their contents determined.
