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An early editor of this Journal characterized it as a living textbook of chemistry. Presumably this was intended
to mean that, like a textbook, the Journal contains a
wealth of information that has been carefully checked for
accuracy. A living textbook, like a living organism, grows and
matures, constantly updating and modernizing the
information it contains. The Journal's role as a living textbook
was brought home to me most emphatically as the editorial
staff prepared this issue, because that is exactly how we used it.
At the JCE booth at the recent ChemEd '97 meeting
in Minneapolis we handed out lots of copies of the first
JCE Classroom Activity sheet (see last month's issue)
together with small refrigerator magnets that could be used to
carry out the activity. Reaction of the teachers at the meeting
was so positive, and so many said they would like an
activity sheet in every issue, that we changed our plans and
decided to do one for this issue as well. But what to do? And how
to do it? The modern incarnation of the living textbook
of chemistry came to the rescue.
Since we had a paper by Dana Barry (page 1175)
about chemistry and trees, and since it is fall, we thought
that the color of fall foliage would make a good activity.
Knowing that anthocyanins are responsible for many of the
fall colors, we immediately thought of red cabbage as an
acid-base indicator, but decided that many, if not most,
readers would already be aware of the many chemistry
activities based on red cabbage (1). At this point we turned to
JCE Online and the Journal's online index. In a few seconds
a search was done to find all titles that contained
"pigment". There were 28. Another search was done for titles that
contained both "acid-base" and "indicator" (9 hits), and
another for titles that contained "anthocyanin" (2 hits, both very
recent and one with its abstract online).
I certainly commend this index to you. It is available free via JCE Online
(http://jchemed.chem.wisc.edu/). Follow the links to Journal and JCE Index. In less than 10
minutes I had found more than a dozen directly applicable
references and more than a half dozen more that were
relevant, but, because of potential hazards, not useful for
a hands-on investigation that could be used as a
take-home activity. Kudos and thanks are due Paul Schatz and
Jon Holmes for making this excellent resource available via
the web 24 hours a day, seven days a week. Every author,
or potential author, of a Journal paper should consult the
index before starting to write.
My search gave me all the information I needed. I
discovered that in the twenties Ernest H. Huntress of
MIT had published three papers on the chemistry of
red and blue pigments of flowers and plants
(2). From these papers I learned that Willstätter's Nobel Prize
was largely due to his work with plant pigments and that the
mass percent of anthocyanins in flower petals varies from about 2% in
purple delphinium to as much as 33% in dark blue-black pansies. The
Journal revisited this subject in a Report of the New England Association of Chemistry Teachers in 1946 that also dealt with other leaf
pigments, chlorophylls and carotenoids. In 1949 a paper on plant
pigments and photosynthesis immediately preceded one
by Melvin Calvin on photosynthesis. Another review of
pigment chemistry appeared in 1982, and there have
been seven papers on different chromatographic separations
of plant pigments. (You'll have to use JCE Index to find
these, as I haven't space to list everything I found.)
Because chlorophylls and carotenoids are not
water soluble, their separation requires flammable solvents,
and for a take-home activity we turned to other sources. An
excellent review on indicators by Szabadváry
(3) had an interesting section on natural indicators, and a paper
by Forster (4) provides lots of good ideas for using
red-cabbage indicator, some of which we applied to flower-pigment
indicators. In 1985 Mebane and Rybolt wrote on "Edible
Acid-Base Indicators" (5), listing pHcolor behavior of 14
fruit and vegetable extracts. Finally, a collaboration of
high school and college teachers has recently provided
excellent information on anthocyanins (6). These papers formed
the basis for developing this month's JCE Classroom
Activity sheet (pages 1176 A and B).
JCE Index even provided ideas for expansion of the
activity. Kimbrough (7) has described a column
chromatographic separation of leaf pigments that requires
only household chemicals (albeit mineral spirits is used),
and Mewaldt, Rodolph, and Sady (8) have devised an
inexpensive and quick chromatographic separation.
Combining these two could lead to another more advanced activity
using fall leaves.
I was personally fascinated by what I found in
this Journal on the subject of plant pigments, and I think
any teacher would be. The willingness of chemistry teachers
to share their ideas and information, the good judgment of
previous editors who published their work, and Schatz
and Holmes's JCE Index, which makes it possible to find
all these papers in a very short time, combine to make
this Journal a unique resource. At 74 years of age this
Journal is full of wisdom, but also growing and maturing. It is
definitely a living textbook of chemistry.
Literature Cited
1. Shakhashiri, B. Z.,
Chemical Demonstrations: A Handbook for Teachers of
Chemistry, Vol. 3; University of Wisconsin: Madison 1989; pp 5057; Sarquis, A. M.; Sarquis, J. L.,
Fun With Chemistry, Vol. 1; Institute for Chemical
Education: University of WisconsinMadison; 1991, pp 5361.
2. Huntress, Ernest H.
J. Chem. Educ. 1928, 5, 1392,
1615; Huntress, E. H. J. Chem. Educ.
1929, 6, 52.
3. Szabadváry, F., translated by Oesper, R. E.
J. Chem. Educ. 1964, 41, 285.
4. Forster, M. J. Chem.
Educ. 1978, 55, 107.
5. Mebance, R. C.; Rybolt, T. R.
J. Chem. Educ. 1985, 62, 285.
6. Curtright, R. D.; Rynearson, J. A.; Markwell, J.
J. Chem. Educ. 1994, 71, 682; Curtright, R.; Rynearson, J.
A.; Markwell, J. J. Chem. Educ.
1996, 73, 306.
7. Kimbrough, D. R.
J. Chem. Educ. 1992, 693, 987.
8. Mewaldt, W.; Rodolph, D.; Sady, M.
J. Chem. Educ. 1985, 530, 987.
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Citation
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