In thermodynamics, transformation equivalents is an early synonym for the quantity entropy, used in 1878 by Scottish physicist James Maxwell, a verbal conjunction of the earlier terms: “equivalence-value” (1854), “equivalence-value of all uncompensated transformations” (1856) and “transformational content” (1865)”, "equivalence of transformations" (1875), etc., used by German physicist Rudolf Clausius.

The concept of "transformations equivalents", according to a condensed Clausius perspective, the term “equivalence value of transformations” means that when several units of heat pass through a body they will effect a conversion of heat into work, according to the phenomenon of the mechanical equivalent of heat, and in other cases, when molecules collide or do work on each other inside the system that such work will be converted into heat, means that will exist a certain amount of heat added to a body, causing it to expand, less a certain amount of heat removed from the body, causing it to contract, that will exactly compensate or balance the heat-work conversions inside the body that took place during the process which brings the body back to its original state. [2]

The following are related quotes:

“By the introduction of the expression, “without compensation” (verses “of itself”), combined with a full interpretation of this phrase, the statement of the second principle (“that heat cannot without compensation pass from a colder to a warmer body”) becomes complete and exact; but in order to understand it we must have a previous knowledge of the theory of transformation-equivalents, or in other words entropy, and it is to be feared that we shall have to be taught thermodynamics for several generations before we can expect beginners to receive as axiomatic the theory of entropy.”
James Maxwell (1878), “Tait’s Thermodynamics” [1]

1. (a) Maxwell, James C. (1878). “Tait’s ‘Thermodynamics’ (I)”, (pgs. 257-59). Nature, Jan. 31.
(b) Maxwell, James C. (1878). “Tait’s ‘Thermodynamics’ (II)”, (pgs. 278-81). Nature, Feb. 07.
2. Clausius, R. (1865). The Mechanical Theory of Heat – with its Applications to the Steam Engine and to Physical Properties of Bodies (Forth Memoir). London: John van Voorst, 1 Paternoster Row. MDCCCLXVII.

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