Calculating the Van der Waals equation of state B constant
 

I'm trying to work out the B constant for hydrogen gas.
I've read in a journal article that it is 7.691x10-3 m3 /kg. But whenever I try to work it out using the information I can find online I get something in the region of 1.3x10-2 m3 /kg. Can anyone help me out ?

By the way the journal article is "Characterization of high-pressure, underexpanded hydrogen-jet flames" by Schefer et al , 2007.

Also if anyone could help me out with a way to calculate the B constant for a gas mixture that would be really helpful.

Thanks