Fed up with the charts for Molecular weight in ASTM D2502?

[jmw]

I need to discover if there is a calculation method for the molecular weight of hydrocarbons consistent with ASTM D2502 or an acceptable alternative, i.e. acceptable to the hydrocarbon industry.
Our dual viscometer method already allows us to determine the density, base density (API) and the kinematic viscosity at two different temperatures. Hence we can already provide such calculations as CCAI and CII Ignition Index (for fuel oils), Viscosity Gravity Gradient (ASTM D2501-91) and Viscosity Index (ASTM D2270-93). However, the molecular weight standard ASTM D2502-92 has a combination of charts and tables to work out the resultant molecular weight from the kinematic viscosity at 40degC and 100degC. The tables we could manage but the charts are a problem.

 

[radomir]

Those chemical gurus should offer help. Me as a dumb mechanical engineer know that if there is only one compound e.g. C6H6 (I do not know its chemical name, I like to call it the primary "honeycomb&quot simply multiply atomic mass with a number of atoms for each element and sum them.

Therefore (12x6)+(1x6)=78 amu

But if there is a mixture of different hydrocarbons and not all known than ASTM is unfortunately unavoidable probably deriving some mean or equivalent molecular mass (once upon a time called weight).