pattern:
methane - 1 carbon, 4 hydrogen. 1/4 ratio
ethane - 2 carbon, 6 hydrogen. 1/3 ratio
propane - 3 carbon, 8 hydrogen. 1/2.666.... ratio
butane - 4 carbon, 10 hydrogen. 1/2.5 ratio
pentane - 5 carbon, 12 hydrogen. 1/2.4
hexane - 6 carbon, 14 hydrogen. 1/2.3333....
heptane - 7 carbon, 16 hydrogen. 1/2.857.....
octane - 8 carbon, 18 hydrogen. 1/2.25
basically, continue to add one carbon and 2 hydrogen.
i believe that will make a curve
octane is heavier than methane. from methane to octane, the density, and melting point is raised