The Two Calories

Abstract

THE suggestion made by Dr. Russell in his letter in NATURE of Feb. 4, that the kilowatt hour with its multiples and submultiples is the best unit of heat, is not new. Some years ago Ostwald proposed the unit of a kilojoule, and recalculated all the thermal data to the new unit. The figures will be found in his “Grundriss der allgemeinen Chemie,” 1909. The reason why such a unit is not adopted in thermochemistry is that all the data would then depend on each redetermination of the mechanical equivalent of heat. The accuracy with which the latter is known probably does not, as yet, exceed one in a thousand, and thermochemists prefer not to have an error of this magnitude involved in determinations which are claimed to have an accuracy of one in ten thousand.