Historical Background of the First Law

Credit for discovering the first law of thermodynamics is attributable to several individuals. We shall single out four key contributors for special mention Rumford, Mayer, Joule, and Helmholtz. A brief account of their contributions allows us to better appreciate the difficult concepts embodied in the first law (interconvertibility of heat and work, and conservation of their total). It also illustrates the vital mix of inspiration, experimental verification, and rigorous theoretical formulation that may be required to bring ideas from the domain of creative speculation to well-established scientific law. 

Rumford s studies (along with those of Humphrey Davy see Section 3.4) contributed to gradual decline of the caloric theory of heat and its replacement by the modem kinetic molecular theory. By about 1840, the interconversion of heat and work was clearly understood, as well as the association of heat with molecular motion. However, there was as yet no clear statement of the conservation principle for the total heat plus work. 

Credit for the first recognizable statement of the principle of conservation of energy (heat plus work) apparently belongs to J. Robert Mayer (Sidebar 3.2), who published such a statement in 1842. Mayer also obtained a (slightly) improved estimate, approximately 3.56 J cal-1, for the mechanical equivalent of heat. Mayer had actually submitted his first paper on the energy-conservation principle two years earlier, but his treatment of the concepts of force, momentum, work, and energy was so confused that the paper was rejected. By 1842, Mayer had sufficiently straightened out his ideas to win publication, 

Classical and Geometrical Theory of Chemical and Phase Thermodynamics. By Frank Weinhold Copyright 2009 John Wiley Sons, Inc. 

That doubt was emphatically removed by the precise experimental work of James P. Joule (Sidebar 3.3). In the years 1840-49, Joule carried out a classic series of studies of the interconversion of work and heat in multiple forms, replacing vague speculations with a firm experimental basis for the first law. Specifically, Joule studied the heating effects of 

---