Fractional abundances as a function of the kinetic temperature. T_k is derived from ammonia (Fontani et al. 2011). The four panels show sulphur-bearing molecules that contain only carbon (top left panel); carbon and hydrogen (top right panel); only oxygen (bottom left panel); and anything else (bottom right panel). The symbols without uncertainty are upper limits. The numbers below the label of each molecule are the Pearson ρ correlation coefficient. The curves represent linear fits to the data, including the upper limits plotted in logaritmic scale.