Re: Partial pressures

[John Denker <jsd@MONMOUTH.COM>]

At 08:25 AM 3/29/00 -0500, Herbert H Gottlieb quoted from Science Links,
vol. 14, page 45,

> "Ordinary air is about 21 percent oxygen and 78 percent nitrogen.  Under
> water, each gas exerts its own pressure, independently of the other.

Right.

> "That means the compresed air that a diver breathes at 10 meters actually
> has 42 percent of the total pressure due to oxygen alone.

That's just not right.  By the aforementioned independence principle, 21
percent of the higher pressure is oxygen.

The right way to say it is that at 1 atm, you have 21% oxygen which
contributes 21 kiloPascals of pressure.  At 10m depth, you have 21% oxygen
which contributes 42 kiloPascals of pressure.