ABSTRACT
The first law of thermodynamics is essentially a 'balance sheet of energy'. It gives the precise relationship between the familiar concept of work and the new concepts of internal energy and heat, both of which we shall be defining shortly. At the beginning of the nineteenth century, the dominant theory as to the nature of heat was that it was an indestructible substance (caloric) which flowed from a hot body, rich in caloric, to a cold body which had less caloric. Heat was quantified by the temperature rise it produced in a unit mass of water, taken as a standard reference substance. Gas is forced at a constant pressure and at a steady rate through a small hole, or series of holes, to emerge at a constant pressure. The series of small holes is usually in the form of a plug of cotton wool or similar material.
