| Popis: |
An apparatus is described for recording small temperature changes of the order 0.01° C. to an accuracy of 0.0002° C. The thermosensitive element used is a thermistor which forms part of a d.c. Wheatstone bridge. The bridge is automatically balanced by feeding back an a.c., proportional to the off-balance current, to heat a second thermistor in the opposite arm to the first. The magnitude of the a.c. is a measure of the temperature of the first thermistor, inside the calorimeter, and is recorded on a suitable instrument. The apparatus is calibrated by feeding into the calorimeter known amounts of electrical energy from a small heating coil. The apparatus has been used for the determination of heats of wetting and of adsorption when fine-grained powders are immersed in various liquids and solutions. |
