Thermal reactions between the different solid constituents in mixtures can be detected by graphical treatment of the derivatographic curves of the components in the isolated state and of the multi-component system. To solve this problem, the introduction of relative thermal curves (RTA), i.e. relative DTA (RDTA), relative DTG (RDTG) and relative TG (RTG), is proposed. Their construction and use are presented using the example of the thermal decomposition of mixtures of the crystallohydrates of copper nitrate (CNT) and chromium nitrate (CNN).