Density of Gas

[rayosclx]

In fluid_properties(), case oil_api=0, the cited eq. 1.64 should have M instead of gas_grav. Because M=Magas_grav, and Ma= 28.9625 lbm/lbm-mol, then just replace gas_grav for 28.9625gas_grav. Densities will now make sense.
Nice function, saved me a lot of time.