RE: Symbols for chemical bonds

From: Ernest Cline (
Date: Thu Apr 07 2005 - 16:27:35 CST

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    From: Jukka K. Korpela <>
    > On Wed, 30 Mar 2005, Ernest Cline wrote:
    > > 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.

    The semantic argument is a reasonable one, but IIRC Unicode policy
    is that if that unless needed for legacy sets, not to make distinctions
    between symbols of the same general grouping, such as that
    unless there are clearly distinguishing visual features for them or
    a real possibility that a meaning might be obscured by using the
    same character. The four chemical bond symbols and the four
    math symbols are of the same general group. Your points 2 and 3
    address the visual features, and after I respond to them, I'll address
    the possibility of non-visual confusion.

    > 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.
    > ...

    While a chemical author would likely prefer to have four bond symbols
    of the same width and with strokes of the same height, such visual nicety
    is not essential to understanding their meaning. A reader should have
    no problems distinguishing that bonds are meant nor how many bonds

    > 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.

    This is very much a font issue rather than a symbol issue.
    The width carries no meaning and adding new symbols
    would mean waiting years before they could be reliably used
    Using appropriate fonts can address the concerns of Chemical
    authors over these symbols today. I'd want more than minor
    visual details that don't obscure the meaning before adding
    separate chemical bond symbols.

    So is there a type of a confusion that could be caused by
    looking at a plain text version of text containing characters used
    both for chemical bond symbols and math symbols?

    From my own admittedly limited experience, I would say no.
    If someone presents examples where confusion could result,
    I would reverse my position and endorse adding all four bond
    symbols as characters, as it makes no sense to add only a
    subset of these even if the confusion were possible on some
    of these.

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