Calorimeter (Lat. color, heat, and Gr.Calorimeter 0300339 , measure), an instrument for measuring quantities of heat, without making any assumption as to what heat is. One of the first employed for this purpose was contrived by Lavoisier and Laplace, and was directed to determining the comparative quantity of heat developed by the combustion of definite amounts of fuel. The combustion was effected in a cylinder, which was let down into a larger one filled around with pounded ice. Another cylinder outside of all also contained ice, which prevented that in the middle cylinder from being affected by the external temperature. The heat from the innermost vessel caused the ice to melt in the cylinder next to it, and the water thus produced ran off through a pipe passing through the bottom. The practical application of this principle, however, did not give correct results, all the water not leaving the ice, and on account of the relatively large quantity required of the material to be examined and the consequent impossibility of determining the specific heat of many rare substances. Bunsen in 1871 modified the apparatus in a way that enabled him to measure the volume of ice melted by the contraction which this ice undergoes on liquefaction.

Count Rumford's method was to substitute water for ice, and to determine by delicate thermometers the increase of temperature in a definite weight of this liquid by the absorption of the heat. Other forms of apparatus have been invented by Dulong, Favre, Silbermann, Regnault, Despretz, and others.