From: Jukka K. Korpela (firstname.lastname@example.org)
Date: Thu Mar 31 2005 - 11:29:47 CST
On Wed, 30 Mar 2005, Ernest Cline wrote:
> The texts I've seen lead me to believe that in some circumstances the
> existing minus sign, equals sign, identical to, and strictly identical to
> characters are employed in linear text to represent simple single to
> quad bonds.
I think it is more common to use either hyphen-minus or en dash for a
single bond. Especially if you only need to write single and double bonds,
using just ASCII characters looks very safe. And even if you use something
longer for a single bond, the odds are that en dash works much more often
than minus sign.
Anyway, _some_ characters are used in linear text for the bonds. E.g.,
which contains both such usage and two-dimensional formulas.
I have often seen formulas containing the bonds in common encyclopedias
and other books intended for a wide audience.
> At most, this suggests including glosses to those existing
> characters for their use in chemistry instead of adding new characters
There are two or three problems with this:
1. It is illogical to use characters with fairly definite semantics
for something completely different. I haven't studied how well the
defined properties of the four characters mentioned actually
suit their use as bond symbols, but if they do, that's a coincidence.
2. The glyphs are not of the same width except by accident, but the
meaning of bond symbols would rather naturally call for glyphs
of the same width. Admittedly the widths for the four symbols mentioned
above are the same or almost the same in many fonts, but there are
also considerable differences. In Arial Unicode MS, the widths are
the same except for en dash, which is a little narrower than the
others. In Lucida Sans Unicode, EN DASH is a little narrower
than IDENTICAL TO and much narrower than EQUALS SIGN ; moreover
the lines of IDENTICAL TO are thicker than the other lines,
if the font size is large. In Times Roman, the first three glyphs
are all of different width (and the fourth one is missing).
Of course, this is all to be taken just as a quick check.
Fonts vary, even under the same name, but it is clear that the
four characters mentioned have _not_ been generally designed
in a manner that is suitable for their use as bond symbols.
And why should they? There's no particular reason why EN DASH
should be of the same width as EQUALS TO.
3. The glyphs for the four characters are not very suitable for
use as bond symbols. They should be wider. Or, to put it
milder, the bond symbols should be coded separately to _allow_
font design that makes them wider, or otherwise different
from em dash etc.
-- Jukka "Yucca" Korpela, http://www.cs.tut.fi/~jkorpela/
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