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Re: Gases, vapors and the like



At 12:59 AM -0700 7/22/99, John Cooper wrote:

On Wed, 21 Jul 1999, Leigh Palmer wrote:

A gas is incapable of condensing; that is why one distinguishes
a vapor from a gas. Often the region of a simple phase diagram
for temperatures greater than the critical temperature is called
the "gas phase", but the boundary between this and the vapor
phase below that temperature is evidently artificial.

Well, actually I thought all real gases, He, formula weight 2 and
higher, condense at sufficiently high pressure and low temperature.

Actually you thought a bit imprecisely, John, and I would have said
that all real substances condense at sufficiently high pressure and
low temperature. I don't understand the specification of He and
formula weight 2.

Does a substance cease to be a gas when it condenses in your lexicon?

Beyond the critical point, chemists and chemical engineers refer to the
phase as a fluid, without reference to condensation phenomena at
sufficiently lower temperatures; below the critical temperature/pressure
that fluid phase is called a gas in these circles.

The only thermodynamics textbooks I have here in my office are of
physics and (nonchemical) engineering sort. They all conform to my
stated convention. We physicists speak of a liquid-vapor change of
phase (or sometimes change of state) and never, to my recollection,
to a liquid-gas change of phase. I have a chemist wife, however; I
shall consult her. (I asked her; she agrees with me.)

Isn't it clear words, particularly in a rich language like ours, carry
multiple meanings, which have to be interpreted in context. That's why we
have dictionaries, although even they differ. Mine happens to be quite
clear that 'gas' and 'vapor' can be distinguished because vapor connotes
suspended particles as in a fog. But then we/I say *vapor* pressure to
mean something quite different from *gas* pressure. Engineers talk about
'wet' and 'dry' steam.

I don't use a dictionary for technical terms; I define them, and
they usually have more precise meanings than the dictionaries'
definitions. What you say about language is true, and it often
constitutes an impediment to understanding. If you don't think so,
imagine what treaties between peoples with different languages are
like. I have a linguistic anthropologist daughter (northwest coast
Indians) who can tell you some hair-raising tales.

Rigid adherence to uniform, unitary uses of words, or symbology for
that matter, may simplify the local situation but is inconsistent with the
way language, and symbology, is used even within/among professional
disciplines as closely related as physics and chemistry or chemistry and
chemical engineering. It's a little like _speaking_ as Romans when in
Rome, or _hearing_ for that matter.

In order to be useful as a technical communication medium English
words must be used with precise meanings, conventionally
understood by both parties in dialog. If that sounds pedantic (in
the dictionary sense of seeming formal and uninspired), so what?

I don't want my language to be "inclusive" if I must include those
who will not acknowledge the value of rigor. If that is politically
incorrect, who cares?

Jack Uretsky has remarked cogently on the need to find out what the
question is before expending too much time trying to answer it. Instead
of trying to impose a Pax Physica on the language, why not take the time
to conjure what the other fella is trying to say instead of berating those
who don't say it quite the way we would have? Poets will tell us it is
*differences* in the uses of language by various users that contributes to
the beauty of its expressiveness.

I am a lover of the English language, named for a Victorian poet.
I am a lover of artful English; Mark Twain is my favorite, but
many others contribute to the rich literature I have enjoyed. I
can also communicate in another vocabulary which may sound very
much like English, but those with whom I communicate understand
that our words have more precise and, occasionally, different
meanings from their vulgar homonyms. Not everyone can understand
communication in that second vocabulary. If that's elitist, who
cares?

One-word-one-meaning is something my beginning students yearn for. But
that isn't the way language is used; I prefer Jack's observation that you
have to come at a question/concept from several different directions/
aspects before you can begin to grasp the whole: like the blind men
attempting to integrate their individual experiences of an elephant. I
think of language as a multi-dimensional, non-orthogonal vector space on
which we try to impose and interpret experience. Rotate the frame of
reference and the projection of experience on each unit vector will differ
somewhat. Frames rotate and translate.

You should heed your beginning students' yearnings. Elaborating
that metaphor will not help them; it sounds rather more like an
excuse for unnecessary imprecision in use the of language.

Whenever you encounter a term that has different meanings in
the two vocabularies you should seize the opportunity to point
to the difference - and clarify what you mean by the word.

Language is not the experience; it's only the representation of aspects
of experience. Paring the fruit of experience to fit the confines of
narrow linguistic definitions may well lose the flavor that is
understanding. Linguistic rigidity may well be a first step toward, but
is not the end-all of, understanding.

I teach my students that scientific understanding is of a
circumscribed, severely limited scope; there are vast realms
regarding which science is ignorant and silent. It is for that
reason we do not need a language which is as rich as popular
spoken and written English to communicate our science.

Leigh


Leigh Hunt Palmer Phone: 604 291 4844
Department of Physics FAX: 604 291 3592
Simon Fraser University Home: 604 299 3731
Burnaby, BC V5A 1S6 email: palmer@sfu.ca
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