An isothermal flow calorimeter suitable for measuring heats of reaction and heats of mixing at high pressure is described. With the calorimeter endothermic or exothermic processes can be studied from 0 to 70 °C and from 1 to 400 atm. Energy effects from 0.15 to 30 J/min are measured with a precision of ±0.4% at a constant temperature through the use of an automatic controlled variable heater and a constant cooling Peltier device. A complete heat-of-mixing curve can be generated from a single run. The calorimeter was tested by measuring the heats of neutralization of HClO4–NaOH and HClO4–TRIS and the heat of mixing of n-hexane-cyclohexane, and was found to produce data in very good agreement with published literature values.

A calorimeter for measuring heat output from batteries is described. The calorimeter has a peak-to-peak noise level of 0.3 ~W. A thermodynamic analysis of battery processes is given and a method of using the calorimetric data to study and define parasitic processes is illustrated with data on several batteries.

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An isothermal, isobaric, flow calorimeter suitable for measuring either endothermic or exothermic heats of mixing from 273 to 423 K and from 0.1 to 40.5 MPa is described. Energy effects from 0.15 to 30 J/min can be measured to an accuracy of ±0.5% for standard test systems at a constant temperature through the use of an automatically controlled heater and a constant cooling Peltier device. The calorimeter was tested by measuring the heat of mixing of water-ethanol at 383 K and 1 MPa and was found to produce data in good agreement with published literature values.

An isothermal titration microcalorimeter having a volume of 4 ml and capable of temperature control to ± 2 × 10−5 °C is described. Major components include a constant temperature water bath controlled to ± 3 × 10−4 °C, a platinum reaction vessel, and an isothermal control circuit consisting of constant Peltier thermoelectric cooling and variable Joule heating controlled by a thermistor in an ac Wheatstone bridge circuit. The calorimeter was tested by measuring the heat of ionization of water and was found to produce data accurate to ±0.1% for this system. The instrument is ideally suited for measuring heats where small samples are used such as in the investigation of many biological systems.