Black, Joseph correspondence with

Hills, James Watt. Volume 1, pp. 72-3 J. P. Muirhead, The Life of James Watt with Selections from his Correspondence (London John Murray, 1858), pp. 60-73 E. Robinson and D. McKie (eds), Partners in Science. Letters of James Watt and Joseph Black (Cambridge MA Harvard University Press, 1970). 

By this time, affinity was used routinely by chemists in their judgements and interpretations of observations made outside the lecmre hall. A particularly nice example appears in some correspondence between Joseph Black and James Ferguson in which Black explains that while corrosive calcarious earths will violently attract and dissolve in aU acids, when spar or marble (mild calcarious earths, that is calcarious earths in combination with mephitic or fixed air) are placed in distilled vinegar, they will dissolve eventually, but it takes a very long time because ... 

As was discovered by Joseph Black, the heat absorbed, the latent heat, converts the solid to a liquid at the fixed temperature. Generally this change happens at a fixed pressure, hence we may equate Ag to AH, the enthalpy change associated with melting. The enthalpy associated with the conversion of one mole of the solid to liquid is called the molar enthalpy of fusion AHfus-The corresponding change in entropy, the molar entropy of fusion A5fus can now be written as... 

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