A double twin isothermal microcalorimeter Lars Wadso È a,* , Natalia Markova b a Building Materials, Lund University, Box 118, 221 00 Lund, Sweden b Physical Chemistry 1, Lund University, Box 124, 221 00 Lund, Sweden Received 19 June 2000; accepted 23 June 2000 Abstract The design and properties of a double twin heat conduction microcalorimeter are described. In this instrument two twin microcalorimeters are placed close together, one on top of the other. The size of the instrument is the same as that of a commercial single twin microcalorimeter and each of the twin parts has similar properties as one normal twin microcalorimeter. The cross-talk between the calorimeters can be made low; we measured <0.1% of the signal generated in one calorimeter in the other calorimeter. This ®gure is, however, dependent on how well the two sides of the instrument are thermally balanced. The paper also contains a general discussion of the use of a reference in reducing the effect of temperature changes in the heat sink. The advantage with a double calorimeter is that one may easily perform two related calorimetric experiments at the same time and in close proximity to each other, e.g. both sorption isotherms and sorption enthalpies may be measured simultaneously, or the heat production rate of a biological process may be monitored at the same time as the CO 2 production is measured. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Microcalorimetry; Heat conduction calorimetry; Isothermal calorimetry; Instrument design 1. Introduction Isothermal calorimetry is the measurement of heat and thermal power at constant temperature. This is a very general measurement technique as almost all processes (physical, chemical, biological) produce heat. Isothermal calorimetry is today used to study such diverse processes as microbiological growth, cement hydration and stability of pharmaceuticals and explosives [1±3]. Isothermal calorimeters are primarily used to study processes by the heat the processes themselves pro- duce. There have, however, also been reported more advanced measurements where a second calorimeter has been used to assess a secondary parameter char- acterizing the same process. One example is the simultaneous monitoring of a biological process in one calorimeter and the on-line measurement of the same process' CO 2 -production in a second calorimeter reported by Johansson and Wadso È [4]. The calori- metric CO 2 measurement was made by measuring the thermal power produced when the gas stream contain- ing the CO 2 was bubbled through a NaOH-solution. Another example is a number of sorption calori- meters in which water is vaporized in one calorimeter and absorbed by a sample in another calorimeter [5± 9]. In these instruments one of the calorimeters mea- sures the thermal power of sorption (the sorption enthalpy) and the other measures the thermal power of vaporization (from which one may calculate the mass change and/or vapor pressure of the sample). A Thermochimica Acta 360 (2000) 101±107 * Corresponding author. E-mail address: lars.wadso@byggtek.lth.se (L. Wadso È). 0040-6031/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII:S0040-6031(00)00574-8