From: Houphouet Hy Yarabe <hyarabe@unix1.sncc.lsu.edu>
  To  : rasmb@bbri.harvard.edu
  Date: Mon, 5 Oct 1998 11:10:59 -0500 (CDT)

I need a help on calculating partial specific volume.  Somebody used
the following equation to make the calculation:
 1/density = vbar + W*d(1/density)/dW
I am looking for the exact litterature refence for this formula

Yhanks 

Yarabe