Complex sentence: Sabatier's earliest researches concerned the thermochemistry of sulphur and metallic sulphates, the subject for his thesis leading to his doctorate; and in Toulouse, he continued his physico-chemical investigations to sulphides, chlorides, chromates and copper compounds.
Split into simpler sentences: 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.