Abstract: A calorimeter includes an adiabatic enclosure surrounding a tube for supporting a sample. In the enclosure is a control chamber in thermal contact with the sample-carrier tube and containing a substantially perfect gas. The temperature of the sample is kept constant during a change of state by varying the pressure of this gas. A differential gas thermometer provides an indication of the difference between the temperature of the sample and that of a thermally insulated reference body which is initially at the same temperature as the sample. An automatic control system varies the pressure of the gas in the control chamber in the sense which tends to cancel any temperature variations detected by the differential gas thermometer. The gas pressure is varied by means of a vertical passage which has its upper end connected to the control chamber and its lower end connected to receive hydraulic liquid from a volumetric pump actuated by the control system.

Abstract: A calorimeter for measuring the latent energy of a sample at a pressure of at least 1,000 bars has a test chamber enclosed in a substantially adiabatic enclosure. It has thick walls able to withstand the very high pressure, and is connected by capillary tubing to means for holding it at a set pressure. The test chamber and a reference body which is thermally equivalent to the chamber are surrounded by respective adiabatic jackets and symmetrically arranged in an isothermal enclosure which is held at a set temperature. A differential gas thermometer has bulbs in contact with the test chamber and with the reference body, and a two-input differential pressure measuring unit has each input connected by a capillary tube to one of the bulbs. The pressure measuring unit has a manometer capsule with a respective input on each side of a flexible membrane, a capacitive pickup for sensing the position of the membrane, and electronic readout means. It is enclosed in a thermally insulative case.