From: Ernest Cline (ernestcline@mindspring.com)
Date: Wed Mar 30 2005 - 10:16:30 CST
I goofed and originally sent this just to Jukka
Ernest Cline
ernestcline@mindspring.com
> [Original Message]
>
> > From: Jukka K. Korpela <jkorpela@cs.tut.fi>
> >
> > Which Unicode characters would be most suitable as symbols for chemical
> > bonds? By visual appearance, one might think about using
> > - em dash (or en dash) for single bond
> > - equals sign for double bond
> > - identical to for triple bond
> > - strictly equivalent to for quadruple bond
> > but these would differ quite a lot from the usual semantics of the
> > characters (except for the em dash, which is rather general-purpose
> > anyway). Besides, there would hardly be any guarantee that all the
glyphs
> > would be of the same width in a given font.
>
> I would expect (and a casual inspection of a few fonts supports my
> expectation) that minus sign, equals sign, identical to, and strictly
identical to
> would all have identical widths. However...
>
> > I found the document "Elsevier Science Grid in Unicode",
> > http://support.sciencedirect.com/sgml/dtd50/esgrid.pdf
> > which discusses the mapping of a large number of symbols
> > to Unicode characters, and it contains no Unicode equivalents
> > for the bond symbols.
>
> ... the ESGrid provides several complications.
>
> First, for the double, triple, and quadruple bonds, it contains two
versions
> that vary only in size. One set is described as em dash in width (which
the
> set of characters I gave above are usually narrower than) and the other is
> described as being 6 point.
>
> Second, it provides for three glyph variants for a partial double bond
> and two for a partial triple bond. One of the partial double bond
equivalents
> is equated in the ESGrid to U+2393. This indicates that trying to
provide a
> one-to-one mapping from the ESGrid to Unicode might not be desirable.
>
> Finally, the ESGrid has bond "characters" such as "lbond3" that are
> clearly intended to serve as graphics primitives and not as part of linear
> text as they serve to point to items that aren't in the same line of text.
>
> > Since bond symbols are often used in chemical formulas inside texts
> > it would seem natural to encode them as characters.
>
> I would tend to disagree. Chemical bond indicators appear to be
> graphical and not textual. In particular, the fact that they cannot be
> confined to a line of text causes me to reach that opinion.
>
> While there may be some things in the ESGrid worth encoding in Unicode,
> the chemical bond glyphs are not among them in my opinion.
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