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From: cjh@petsd.UUCP (Chris Henrich)
Newsgroups: net.physics
Subject: Re: Hydrogen (isn't flammible?!?) (vs. Helium in dirigibles)
Message-ID: <488@petsd.UUCP>
Date: Wed, 3-Apr-85 16:45:28 EST
Article-I.D.: petsd.488
Posted: Wed Apr  3 16:45:28 1985
Date-Received: Thu, 4-Apr-85 06:41:24 EST
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Organization: Perkin-Elmer DSG, Tinton Falls, N.J.
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[]
	Apropos of the Graf Zeppelin, Theodore Swift writes:
>                                                           Four times
> strikes me as off, since hydrogen, though of atomic weight 1.00X,
> is diatomic.  Thus it would only have "twice" the lifting power.

	The difference in lifting power between H2 and He is
smaller than that. Consider that lifting power comes from the
_difference_ between the weight of the lifter and that of the
surrounding fluid (in this case, air).  A standard volume
(22.4 liters?) of gas with a molecular weight N, at standard
temperature and pressure, masses N grams.  The average
molecular weight of the mixture of gases in air is about 29.
now...
             Mass of Gas    Mass of Air   Buoyancy
H2           2              29            27

He           4              29            25

(That is, 22.4 liters of H2 will lift 27 grams, but 22.4
liters of H3 will lift 25 grams.)  So hydrogen is "better" by
a whopping 8 percent (weeping wizards!)

	Hydrogen is also much easier to obtain by chemical
processes.  But, of course, it burns.

	My recollection is that the Germans wanted to use
Helium, for safety reasons, and the USA refused to sell it to
them, because it was used in some munitions-making process.

Regards,
Chris

--
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