One of the examples I was looking at had to do with diffusion of hydrogen in a Pb sheet. There is a constant concentration gradient applied, so the hydrogen is constantly diffusing. We are able to determine the concentration of the Pd matrix. We further know the atomic weight percentages of the hydrogen at either end of the concentration gradients. Let's say 1 at. % at one end, and 0.2 at. % at the other. To determine the concentration of hydrogen, he merely multiplied the concentration of Pd by the percentages (0.01, 0.002). Is this correct? I though you would have to multiply TOTAL concentration of both hydrogen and Pd atoms? The atomic percentage of atom A is number of A atoms/(number of A atoms + number of B atoms)??