Histogram of isotopic quotients (log Q
and log Q
) for 285 natural gases (Table 1). All values of Q1,2 and Q1,3 were calculated as described in Table 1. The arrows beneath the chart (catalytic gas) mark the positions of log Q1,2 and log Q1,3 for Catalytic Gases in Table 1. The vertical lines mark isotopic equilibrium constants at 300 K, log K1,2 = 0.31259; log K1,3 = 0.49602, and at 500 K, log K1,2 = 0.30786; log K1,3 = 0.49142 .