Tunell G. On the history and analytical expression of the first and second laws of thermodynamics, and the rôle of the differentials, dW and dQ

The Journal of Physical Chemistry, 1932, Vol. 36, No. 6, pp. 1744–1771.The entropy introduced into physics by Clausius was, contrary to general belief, not a new physical quantity but the reconstruction of the 'quantity of heat' conceived about one hundred years earlier by the Scottish chemist Black. The same quantity was also used under the name 'calorique' by Carnot in his work which laid the foundations of thermodynamics. That entropy and Black’s 'quantity of heat' are only two names for the same physical quantity is not only of historical interest but is of significance to the teaching of thermodynamics as well. It asserts that entropy can be visualised as a kind of substance which obeys 'half a conservation theorem': it can be created but not destroyed.