We must remember that there are two common ways of expressing the 
proportion of a particular gas in a mixture - by volume and by mass. I have 
always assumed that the commonly stated ratios of air, i.e. roughly 20% 
oxygen/ 80% nitrogen were expressions by volume. (I could be wrong 
however). In this case we cannot calculate the mass of EanX mixtures using 
these ratios.

FYI, the relative masses of Helium, Nitrogen & Oxygen are 1:7:8 
respectively (in both gas and single atom form).

Ben Carbery

-----Original Message-----
From:	CaptnDale@ao*.co* [SMTP:CaptnDale@ao*.co*]
Sent:	Thursday, February 11, 1999 5:05 AM
To:	darkangel@en*.co*; techdiver@aquanaut.com
Subject:	Re: Weight of air.

In a message dated 2/10/99 7:20:39 AM Central Standard Time,
darkangel@en*.co* writes:

<< OK thats for EanX21.

 Has anyone given any thought about how the use of richer EanX mixtures 
(say
32% or 36% O2) affect the gas weight?
 Or what is the relative weight of the Nitrogen and Oxygen in the mixture.
 Taking it further, how about adding helium.

 Perhaps it would be better to state the weight of Oxygen, Nitrogen and 
Helium
seperately per liter @ 30C and 1 bar?
 One could calculate the weight of the carried gas easily from that.
  >>

I believe that the weight of a gas in a mixture is proportional to its
molecular weight times its fraction in the mix.  Since Oxygen and Nitrogen 
are
right next to each other on the periodic chart they are very close in
molecular weight.  For practical purposes it would not be worth the trouble 
of
calculating the differing weights for various EANx mixes.  They would be
nearly the same.  Trimix, on the other hand, will be significantly lighter.

Good diving,
Cpt. Dale Bennett
Captain Dale's Dive Center
Enterprise Marine Dive Charters
CaptnDale@ao*.co*
www.captaindales.com
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