Determination of the Mechanical Equivalent of Heat

In the mid-19th century, Joule published his results on the mechanical equivalent of heat in the Philosophical Transactions of the Royal Society. The central idea of measuring the relationship between mechanical energy and heat energy by means of a friction apparatus quickly found its way into teaching and led to a large number of different teaching apparatuses that used this principle. One variation of these friction apparatuses is the Callendar apparatus.

The apparatus, designed by Hugh Longbourne Callendar, was patented in 1903 and consists essentially of a rotatable, cylindrical calorimeter made of thin brass into which water is filled and in the plug of which there is a thermometer for measuring the temperature inside. Around the calorimeter is a silk ribbon, to which weights of known mass are attached in order to pull the silk ribbon taut over the cylinder body. When the cylinder rotates, the belt rubs against the cylinder shell and the heating of the surface is successively transferred to the cylinder contents. Based on the number of revolutions, one can now calculate the mechanical energy for the movement of the cylinder and set it in relation to the heat input, which is determined by the temperature change of the water.

In the experiments with the Callendar apparatus located in the HistoLab, our former student and current colleague Ruben Holländer succeeded in understanding the work process. The value of the mechanical equivalent of heat determined with the Callendar apparatus only shows an inaccuracy of about 0.5% compared to modern literature values.

literature

J. P. Joule, "On the mechanical equivalent of heat," Philosophical Transactions of the Royal Society of London, vol. 140, pp. 61–82, 1850-01, doi: 10.1098/rstl.1850.0004.

H. L. Callendar, "Improvements in Apparatus for Measuring the Mechanical Equivalent of Heat," GB190213377 A, 1903-06-11 Accessed: 2019-09-12. [Online]. Available: https://worldwide.espacenet.com/publicationDetails/biblio?FT=D&date=19030611&DB=EPODOC&locale=en_EP&CC=GB&NR=190213377A&KC=A&ND=5

C. S. I. Company, Callendar’s Apparatus for measuring the Mechanical Equivalent of Heat. Cambridge, 1906. Accessed: 2019-08-08. [Online]. Available: https://sil.si.edu/DigitalCollections/Trade-Literature/Scientific-instruments/files/51711/index.htm