jon is right there is a specific gas doc out there. I own the fricken thing and have read it, but it is buried in some boxes I have in storage and I can't remember its designation. Its A5 if I remember right.
It talks about Ar, He, CO2, N, H, etc., singles, bi mixes, tri mixes, quad mixes, short circuit, spray, globular, rotational transfers, carbons steels, low alloys, stainless steels, non ferrous alloys, GTAW, GMAW, FCAW, and PAW, heat transfer, penetration patterns, ionization potentials, mass, chemical activity, element transfer and oxidation, etc, and yes, even flow rates.
Its a great book.