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From: mcdougal@tegra.COM (Steve McDougall)
Newsgroups: sci.electronics
Subject: Re: methanol
Summary: Specific gravity
Message-ID: <1807@riddler.tegra.COM>
Date: 3 Dec 90 19:13:15 GMT
References: <1990Nov28.203618.7294@arcturus.uucp>
Reply-To: mcdougal@riddler.UUCP (Steve McDougall)
Distribution: usa
Organization: Tegra-Varityper, Inc. Billerica, MA
Lines: 49

In article <1990Nov28.2618.7294@arcturus.uucp> graham@arcturus.uucp (Thomas D. Graham) writes:
>
>  Which is, is there any easy way to determine the amount of water mixed
>  in with the methanol????  

Well, it depends how much water you think there is and how exact an
answer you need.  Burning the mixture isn't a good idea, because
if there is lots of water, it won't burn at all, and if there is only
a little, it will evaporate when the methonal burns.

If you only want to know if there is *any* water, you could look for
something that reacts with water but not methaol.  Maybe copper sulfate
(Cu SO4).  This is a white crystalline salt that turns blue in water.
I don't know if it turns blue in methanol; I would guess not.

If you want to know *how much* water you have, probably your best
bet is to measure the density.  For a quick and dirty check, just use
a graduated cylinder and a scale to measure the volume and weight of
a sample.  The density of the sample will lie somewhere between the 
density of water and methonal.  Given the density, you can compute the
amount of water in the sample.  

However, the computation is *not*
straightforward.  The problem is that 1oz water mixed with 1oz 
methanol yields less than 2oz mixture, because the water and methaol
molecules fit together in the mixture.  A chemist or maybe CRC
(Chemical Rubber Company Handbook) might be able to give you the
approproate formula.

The other problem with measuring density this way is that you can't
measure volume very accurately with a graduated cylinder.  I wouldn't
count on an answer better than 5%, espically if there is only a little
water.

A better to measure the density of a liquid is with a flotation device.   
(I don't know what they are really called.)  
It has a thick weighted end that sinks into the
liquid, and a thin hollow end that doesn't.  The thin end has a scale
along its length, and you read the scale where it intersects the surface
of the liquid.  The further into the liquid it sinks, the lower the
density.

These devices are used in places like the beverage industry.  You might
try a do-it-yourself wine making catalog or supply house.  If you're 
lucky, you might find one that is calibrated directly in % methanol, 
although % ethanol is more likely (for obvious reasons).  

N.B. Places that use these flotation things often refer to 
density as "specific gravity".


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