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Benjamin Thompson, also known as Count Rumford, investigated the sustained production of heat by friction during cannon boring. In the water-enclosed experiment, continued mechanical motion heated the surrounding water to boiling. He also compared the thermal behavior of material removed from the bore with that of the original metal, testing whether the heating could be explained by releasing a special store from the chips. The observations helped challenge a finite-reservoir account of caloric and connected mechanical work with the production of heat.^[ref]

His sustained frictional heating observations challenged a finite-store account of heat.

Rumford's cannon-boring experiment tested whether frictional heating could be explained as release of a finite store of caloric. In his 1798 paper, Count Rumford describes rotating gun-metal against a borer while enclosing the heated cylinder in a water-filled wooden box. In Experiment No. 3, the cylinder turned at about $32$ revolutions per minute, and the surrounding water boiled after $2$ hours $30$ minutes.^[ref]

A separate control compared hot metal chips with thin strips cut from the same metal. Mixing equal masses into equal quantities of cold water gave nearly equal final temperatures, challenging an explanation based on a large change in specific heat capacity during cutting.^[ref] Continued mechanical input, rather than depletion of an evident material heat store, was the striking result. A modern quantitative energy balance must also include warming of the apparatus, environmental losses and measured mechanical work; boiling by itself does not determine an exact mechanical equivalent of heat.