On the boiling points of some saturated aqueous solutions

Abstract

Introduction and General Discussion . —These experiments were made so as to obtain as accurate data as we could for the purpose of calculating the osmotic pressures of the solutions. The method for determining the boiling points was that already detailed in an earlier communication to the Society, except that differential platinum thermometers were used as described in the paper “On the Boiling Point of Water.” One of the platinum thermometers was always in the hypsometer, and to get the true boiling point as defined in our previous paper the height of the barometer and height of solution were systematically noted. The chief difficulty of the experiments was that of keeping the solutions saturated. It was found necessary to use a large quantity of finely powdered salt, and to keep the solid in rapid motion by a sufficiently powerful current of steam. If large crystals are used, or if the salt has been left in contact with the solution too long at the end of an experiment, so that crystals have grown, the next experiment will give low values for the equilibrium temperature, showing that the solution is not saturated. At times it happened that a paste of crystals was formed, which offered so much resistance that the steam entered at a pressure greater than normal, thus giving too high a value to the boiling point.