Hello, I have the thermodynamic potential dG = -SdT + VdP - MdB and I find that (dG/dB)_(T,P) = -M and (dG/dT)_(P,B) = -S, where I have used _(letters) to denote constants and that these are partial differentials. I want to prove the Maxwell relation that (dS/dB)_(T,P) = (dM/dT)_(B,P) * so I do (d/dB (dG/dT)_(P,B))_(T,P) = (d/dT (dG/dB)_(T,P))_(P,B) But then bring these partials together, I no longer no what it supposed to be kept constant, or how I get to * Sorry, about the messiness, and cheers for any help. I didn't put this in the homework section because its a pretty general question rather that an actual problem. EDIT: Nevermind, I'm being an idiot. I got it now.