On Fri, 3 Jun 2016 22:18:25 -0700 (PDT), curls
wrote:

Jeff

Alcohol is hydroscopic (absorbs moisture from the air). Your 99% will
go down to 91% if you leave the bottle open. Fortunately, it takes
some time so you don't need to be fanatical about replacing the cover.
https://en.wikipedia.org/wiki/Azeotrope
Note that 70% alcohol is what you want for a disinfectant because some
water is needed to kill of hydrophylic bugs.

I should probably buy some 99% alcohol for lens cleaning, but have
been getting away with using the 91% stuff without streaking.

http://www.ebay.com/sch/i.html?_nkw=99%25+alcohol
Ugh... about $8/pint


Wouldn't have guessed Alcohol is hydroscopic.

Yep. The water absorption for ethanol and water stops at a 95.6% mix
(by weight):
http://www.chemguide.co.uk/physical/phaseeqia/nonideal.html
or for denatured alchohol at 91%.

Incidentally, water absorption in ethanol fuel is a potential problem
in high humidity marine environments:
"How Ethanol Gas Attracts Water from the Air - Demonstration"
https://www.youtube.com/watch?v=YeCyFxoWPpo

Or that water in 70% is
needed to make the bugs go belly up (or blow up).

Yep.
https://www.quora.com/When-is-70-isopropyl-rubbing-alcohol-better-than-91

I was thinking of asking on Freecycle for a thimbleful, if I decide I
need it. I'd certainly offer if I'd bought a pricey bottle and someone
asked.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558