Re: Is alcohol 'proof' a vol/vol or mass/mass percentage?

There might be some some confusion about his topic, but the "proof" is 
definitely meant to be a volume/volume relationship.  The confusion can 
come in just what might be meant by a certain value, for instance 100 
proof representing a 50/50 volume relationship.  If equal volumes of water 
and ethyl alcohol are measured and combined, the final volume is less 
(yes, less) that the sum of the original two volumes.  I believe that the 
value, say 100 proof or 50% represents the relationship between the 
volumes combined, and does not involve the final volume.

For a complete discussion of this topic look under "ethyl alcohol" 
or "ethanol" in the Kirk-Othmer Encyclopedia of Chemical Technology.

Jerry Franzen
franzenj@thomasmore.edu