Peak intensities of the observed molecular lines compared to the envelope mass (M_⊙) of each systems. The dashed lines are linear fits to the data for the cases where a correlation is found. Circles, diamonds, and stars show single, close binary, and wide multiple protostellar systems, respectively. We note that the more massive envelopes show an increase in the peak intensities of DCO⁺ and the low-lying transition of H₂CO, which trace cold gas in the envelope. Molecules tracing warm gas have similar peak intensities regardless of envelope mass.