Abstract: An apparatus is disclosed for measuring the concentration of impurities within a substance by the measurement of the reduction in freezing point of the substance. A container containing the substance is coupled to a temperature variation means such as a solid state thermoelectric device for cooling the substance within the container. A temperature sensor such as a thermistor is mounted in thermal contact with the substance for providing a temperature sensor output in accordance with the temperature of the substance. A first amplifier is connected to the temperature sensor for providing a first amplifier output in relation to the output of the temperature sensor. A second amplifier is connected for receiving the first amplifier output to provide a second amplifier output. Control means receives the second amplifier output for controlling the thermoelectric device in accordance with a preselected standard or program.