Most influential book I have read on thermodynamic. I studied engineering and went straight to the applications of thermo. Thermodynamics is an elegant, nonatomistic study of many of the properties of matter, specifically those that have to do with temperature.
It's an elegant book with few, but well thought out excercises. Really, a joy to read, although it's not easy. Herbert Callen was a damn good physicist, too. He contributed to early nonequilibrium thermodynamics, so his exposition is relevant if you are interested in that field.