Those small impurities that we tolerate in air and water:  are they in
fact necessary, or do we just tolerate them?  I am not talking about
pollution.  I am talking about the difference between the mix that we
call "air" and pure oxygen; the good, clean water we drink and pure
H[2]O.  Do we in fact depend on there being a mixture, and if so, for
what?

Thank you,
Archae0pteryx

Air is mostly nitrogen. This isn't because of human pollution, it's
just the way air is. I can't see how this could be considered an
"impurity." We are not built to breathe pure oxygen. Doing so for long
periods can result in neurological problems.

Well, I guess that's an oops for me.  Thanks, Pink.  I have a sense
that I knew these answers once, but it's been a long time since I was
in a science class.

Water, then.

I am looking for something big, common, and unarguable that I can use
as an example of a principle, the idea being that something pure and
unadulterated isn't actually as practical and beneficial as something
with a small amount of other stuff mixed in.  That 100% pure is too
pure for normal purposes.  (Maybe 99 and 44/100ths is enough.)

Thanks,
Archae0pteryx

Hi,
Destilled water (pure H[2]O) not only tastes insipid, the traces of
minerals in spring water are generally beneficial.  Just got a bottle
of what we have:
in mg/ltr:  Calcium 186, Chlorid 121, Hydrogenated carbonat 1144 (the
water is mildly bubbly), Calium 26.7, Magnesium 36.1, Natrium (sodium)
228, Sulfate 42.

Microbes in the water are probably not beneficial, but our systems
become accustomed to them (the local ones), and in small doses can
become accustomed to those in foreign places, the stuff that gives
rise to ... if you drink the local water when you get off the plane in
Bombay.  But an Indian from there can have the same ... problem if he
drinks the water here.
So, in two senses, the impurities can be useful: the minerals per se,
and the broadened exposure to microbes to "strengthen" resistance.

Whether there is an equivalent effect in air pollution?  It would be
interesting to have a statistic about respiratory problems of natives
in Mexico City and that of visitors there.

I read it here, but have forgotten from whom the quotation was:  "If
it doesn't kill us, it makes us stronger."

Myoarin,

Thanks, I don't need the air if I've got the water.  The minerals are
beneficial?   Can I assert that?  Wouldn't we get them some other way?
 I want to be able to draw an analogy something like this:  "... just
as having a small amount of xxx in the water is actually better for us
than entirely pure water would be."

Again, I'm not talking about pollution at all.

In a collection of poems called "Grooks," published probably in the
sixties, Piet Hein wrote:

Maxim for Vikings

Here is a fact
that may help you to fight
a bit longer:
things that don't act-
ually kill you outright
make you stronger.

This is from memory, but I am confident that it's accurate.  He way
not have been the first or only one to say this, but he definitely did
say it.

Archae0pteryx

The minerals are beneficial (some, anyway), but, of course, we can get
them from other sources (magnesium from bananas to avoid muscle
cramps; calcium from milk for our bones  - and that little in the
water may not add much).
I'd love to be a footnote, but not on this subject.  Well, if it were
"a small amount of iodine in the water", that would be absolutely
correct. We need it and it is so seldom that that is why table salt is
usual "iodized"; salt from evaporation of ocean water, naturally so (I
believe).

Thanks for the quotation, appeals to my Viking ancestry.  Now I think
"mine" is from Schopenhauer, but anyone could have the idea.

Put Myoarin

Although air is almost 80% Nitrogen and Carbon Dioxide, and we do
breathe it into our lungs, we actually do not absorb or use the
Nitrogen at all, and very little of the CO2. But without them, the
differentials in gaseous partial pressures across the alveoli
(breathing units within the lungs) would make it difficult for us to
absorb the oxygen in the correct quantities (which could be toxic as
pink mentioned).

You can also consider that although we "eat" for "nutrition", much of
what we eat goes through our digestive systems and back out without
really being nutritious. For example, fiber (the indigestible
substance that makes up the bulk of most vegetables) is useless as a
nutrient, but without it we wouldn't be able to form feces properly
and would suffer digestive problems.  Thus fiber is an impurity from
the nutrition point of view, but an asset for the wider issue of our
best interest.

Hope this was useful.

telnady

A wee bit of fluoride in the water helps to protect our teeth and
prevent cavities...Does that count?

Oh, dear.  This is all lovely information, thank you, Myoarin,
telnady, and Pink, but it is not helping me with my analogy.  I need
to be able to write a line that says, "... just as a small amount of
xxx in yyy is actually better than [100% purity]."  I'm arguing for
the virtue of a little adulteration, and a good analogy would help my
case.  So a little bit of oxygen in a lot of air isn't the right
example, and minerals in water that might all be found also outside
water won't do either.  Likewise, although the indigestible material
in food is the right general idea, the proportions are way off for the
point I am trying to make--and also I don't want readers to leap to
thoughts of bodily waste when they read my line.  Looks like I asked
the wrong question again.  Rats.  Damn.  Now what?

Archae0pteryx

Perhaps the use of pure gold, usually too soft for practical use, might be helpful:
http://www.jewellerycatalogue.co.uk/gold/gold_alloys.php

Also, while purebred dogs may be desirable for certain
characteristics, a more moderate temerament might be found in a mixed
breed.  There are both positive and negative results from breeding
purebreds (and how pure are they"?  The "adulteration" of mixing
breeds may be incidental but avoiding the pure breed may be desirable:
http://www.yourpurebredpuppy.com/tutorial1.html

Lastly, I;m not so sure the concept of "pure" is even attainable in
most common uses of the term.  No support, just a hunch.

Oh, human12, are you really only the twelfth human?  I'm honored.

Gold might be just what I am looking for.  Might be ... and I can
surely use it ... but it would be perfect if gold were a little too
*hard* without some impurity.  Is there anything like that?

Mixed breeds of dogs won't work for my current analogy, though they're
a good example to remember for other purposes.  Chances are I'll never
run out of occasions to use good analogies.

Whether a thing can truly be pure is immaterial.  The word "pure" has
to be understood metaphorically in most applications, and that is true
of mine.  It nonetheless serves the rhetorical purpose.

Archae0pteryx

My above quotation is from Nietzsche.

This maybe, Archae0pteryx:

"Two important metallurgical principles underlie this development. The
first is that pure copper does not cast well; it tends to develop
bubbles that weaken the finished casting. The second is that no copper
ore is pure; all contain, to a greater or lesser degree, traces of
other elements. The most common of these impurities are iron, arsenic,
antimony, lead, nickel and bismuth -- and each produces copper of
varying quality. Minute quantities of bismuth, for instance, make
copper brittle, while large amounts of lead make it soft. The
presence, on the other hand, of arsenic in copper ore cuts down on the
absorption of the gases that makes copper castings porous -- and thus
ensures a finer product."

http://aryan-nations.org/news/article_2003_12_5_2737.htm

I had been thinking that traces of antimony enhanced some material,
which may be true, but I couldn't find anything.  Probably it was
arsenic in connection with copper.

Perhaps another good example is the mutations that occur in gene
pools.  Let us assume that the 'perfect" or "pure" form of
reproduction produces perfect copies of the parental genes. 
Subsequently all offspring should theoretically develop
characteristics of their parents and no others.  However, due to the
"imperfections" of genetic replication, mutations and other anomalies
occur at very small frequencies that enable subtle differences to
arise between offspring that diverges further as you go down the
generations (what some might call "evolution").  If this were not
true, all of humanity (for example) would be very alike in many
aspects (same color hair, skin, same height, etc) as the proverbial
original parents.

telnady

How's this, from the New England Journal of Medicine?

"Less irritating than soap, alcohol rinses and gels have been in use
in Europe for more than a decade but for some reason are only now
catching on in the United States. They take far less time to use --
only about 15 seconds or so to rub a gel over the hands and fingers
and let it air-dry. Dispensers can be put at the bedside more easily
than a sink. And at alcohol concentrations of 50 to 95 percent, they
are more effective at killing organisms, too. (Interestingly, pure
alcohol is not as effective -- at least some water is required to
denature microbial proteins.)"

Educated Guesswork: Do doctors wash their hands enough? (about 1/8 down the page)
http://www.rtfm.com/movabletype/archives/2004_03.html

This might not fit into your story, but impurities are introduced very
carefully into silicon wafers during the semiconductor manufacturing
process; this is essential for their function in integrated circuits. 
So, it would be correct to say, "As minute impurities in silicon
crystals are essential for modern computers, ..."

Here is a nice explanation (confirming my vague memory from primary
school science):
Semiconductor Manufacturing by Elmer Epistola      
http://www.semiconfareast.com/manufacturing.HTM

HI Archae0pteryx,
You've probably finished whatever it was you wanted this for, but
another example occurred to me (probably too wordy to use, anyway):

Young children not exposed to some dirt, pollens, etc., are much more
likely to have allergies later in life, i.e., too much cleanliness is
not good.
Best,
Myoarin

Thanks for continuing to ponder my question, Myoarin.  I haven't
finished yet, as a matter of fact, so I can still use your comments. 
I think the copper analogy might work best for the present purpose,
and I thank you for that.  The beneficial effects of exposure to dirt
are another good one for which I may have a different use.

One does well to quote Nietzsche whenever possible.

Telnady, thanks for the gene pool idea--another good one with
potential for other purposes.  Likewise the alcohol gels, markj, which
sent me off reading all kinds of things about infections in hospitals
that I'm not sure I really wanted to know.  Neurogeek, your suggestion
is right on the mark in principle, but a little too obscure to be big,
obvious, and well known so my reader does not require any education
about it.  Again, I might be able to make a different use of it.

I think I'll come back to this page in the future for reminders of a
number of good and useful analogies.  Thank you all.

Archae0pteryx