It is great to see someone actually checking the references.

The description in the article is my personal editorial freehand description of the equation on page 384. No reference. Indeed I did not try to use Clausius' terminology. My aim was to present his idea in present day language. If you feel like improving on it, I will not be offended. I referred to the 1850 paper to in order to defer to Clausius' priority in stating the law. I would still prefer to quote the 1850 paper rather than the 1865 one. I have not tried to present the nearly simultaneous 1850 version by Rankine, but I would not object to seeing that done as well, though I think it perhaps unnecessary.