Frank 0. Ellison C. A. Hollingsworth
University of Pittsburgh Pittsburgh. PA I 5260
that contain no hydrogen, including a large number of halocarbons, and many metal carbides. Harold Goldwhite California State University, Los Angeles 5151 State University Drive LOS Angeles, CA 90032 Literature Cited 1. Coldwhite, H.JCham. Educ 1964,41,626
To the Editor: The basic difference between Ellison and Hollingsworth's analysis and mine lies in our different understanding and use of infinitesimals. This is a controversial subject, about which there continues to be much discussion (I). Consider their simple function y = x2. For this, the change in y when x changes from x to x + hz is given by ~ y = ( x + h r ) ~ - x ~ = ! ? x h2r + ( k ) (1) The corresponding change in y when x changes from x - hz toxis A ~ = ~ ~ - ( z - L \ x ) ~ = ~ L \ x -2 ( L \ x )
(2)
Now let hz be infinitesimal (&I. I take this to mean that
Equations 1and 2 then give, for x t 0, and for x = 0, Ay = A{y = 0 (compared with 4x)
(4)
The same results can be obtained by taking the limit of AyIhz or A'ylhz
and identifying (with negligible error compared with A&) d with Ax. Ellison and Hollingsworth retain the term in (hzz2 in equation 1 or 2 when Az is infinitesimal, giving or 43' =-(A&)~ a t x = 0. A# = Literature Cited 1. See, for example, Edwards, C. H. Jr Tha Elstoried Lkudopmnt ofthe Cdedus; SpringerVerlag: New York,1979. 2. Compare ref2, pp 255-256,277-218,34t; Xiesler, H.J. Foundations ofinfinitesimnl C&ulus: Rindle. Weber & Schmidt: Boston,Masssehuset&, 1976; & d o n 2A.
P.G. Nelson University of Hull Hull HU6 7RX England
Carbon and HydrogebWhich Has the Most Compounds? To the Editor:
Regarding Ernest R. Birnbaum's letter on What's the Use? [J. Chem. Educ. 1991, 68, 7121 Alton J. Banks shouldn't have surrendered so easily on the question of whether carbon or hydrogen is i'nund in the largest number of compounds. The answer is not obvious, as was pointed out some time ago in this Journal (1).The hydrogen protagonists overlook the large group of carbon compounds 346
Journal of Chemical Education
Suggestions for Truly Evaluating Texts To the Editor: Recently, when several faculty members here were selecting a text for a new general chemistry course, one of them reproduced copies of vour Journal's reviews of most books now in use. &king at the reviews all together, I was struck bv how similar they were. Granted. the books themselves &e quite similar, i s few book companies have the courage to do something different. But the reviews had no "bite." Then I realized that the reviewers have not taught from the books before writing the reviews. Surelv all of us have had thc expcricnce uf flippingthrough book; trymgto find one for adoptim, picking one, and then finding - it to be a disaster when you use it with an actual class! We used Zumdahl's second edition in our general chemistry course. In the second half, which I us&, there were some terrible messes. Especiallv the c h a ~ t e r son kinetics. thermodynamics, and &clear chemistry contained mis: conceptions and outright errors. When I looked a t your reviewer's comments (Haworth, D. T. J. Chem. Educ. 1989, 66, A231), his most serious criticism was ofreflectionofthe light from his desk lamp by the yellow pictures! Virtually all books treat kinetics poorly. Most authors use the same examples, most don't really know how termolecular reactions work, and they fail to realize that probably the major class of unimole&lar reactions in the real world is photolvsis! It's a pity that coverage of kinetics is so poor deipite
