Sabatier's earliest research concerned the thermochemistry of sulfur and metallic sulfates, the subject for the thesis leading to his doctorate. In Toulouse, he continued his physical and chemical investigations to sulfides, chlorides, chromates and copper compounds. He also studied the oxides of nitrogen and nitrosodisulfonic acid and its salts and carried out fundamental research on partition coefficients and absorption spectra. Sabatier greatly facilitated the industrial use of hydrogenation. In 1897, building on the recent biochemical work of the American chemist, James Boyce, he discovered that the introduction of a trace amount of nickel (as a catalyst) facilitated the addition of hydrogen to molecules of most carbon compounds.