Polymer Prlnclples To the Editoc
(1)An experiment measuring only the wavelength of the Balmer series was described hv J. Hollenbere IJ. Chem. Edue. 1966. usid a Beckman DU an.,: 43.2161. In that naoerihe authors ~~~~~~~~~tr&h&meter, which has two disadvantages: the stron&t lineof fi56.3nm is not well observed due to the lower aensitivity of the detector to red light, and the effective spectral slit width of the monochromator is not constant with X. (2) The same experiment described by Douglas can also be earried out with any UV-vis spectrophotometer that may be used in sinele-beam mode. In narticular. we used a Varian 634 S ~neetro&atametereouinnk . . . with ;deuterium lamo: the munuchromator prating has a Czery-Turner mounting, with 32- X 27-mm ruled area and 1276pooves per mm. Push in the single-beam button, select 0.2-nm spectral hand pass, and adjust the energy control (amplifier gain) up to a readout of for the 'I 656-nm ) line. Turn the monoduo2W %T (or 100 % mator until the readouts of the other lines are obtained.In our case only the 656-, 486-, and 434-nm lines were detected well enough to allow suitable calculations to be performed hy the students. Finally, the use of a deuterium lamp instead of a hydrogen lamp as a source of W light isnot relevant in this experiment, because the values of Rydberg constant for atomic hydrogen and atomic deuterium are 1.096775X 107 m-I and 1.091073 X lo7m-', respectively, which supposes a slight shift to shorter wavelength; for example, an emission of 656.1 nm for atomic deuterium versus 656.3 far atomic hydrogen. ~~~~
In the article "Classroom Demonstration of Polymer Principles" [J.Chem. Educ. 1987,64,886], the decomposition of benzoyl peroxide t o benzoyl radicals is indicated. Benzoyl peroxide is known to decompose thermally by bond to benzoyloxy radihomolysis of the peroxide (0-0) cals, which fragment further to give carbon dioxide and phenyl radicals. (See Kirk-Othmer Encyclopedia of Chemical Technology; Wiley: New York, 1967; p 802.) Tonson Abraham The BF W r i c h Company Elastomers and Latex Division TechniCal Center P.O. Box 122 Awn Lake. OH 44012
To the Editor Abraham is correct, of course. I regret not only having made this error but also having allowed i t t o persist. F. Rodrlquez SchWl of Chemical Engineering Olin Hall h e l l University
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Jose L. Guhi6n Dto. lngenlerla Quimlcay Nuclear Univefsi5ad PolnBCniCa de Valencia 46071 Valencia, Spain
Ibca. NY 14853
To the Editor
The Spectrum ot Atomic Hydrogen To the Editor: Recentlv a n interestme laboratorv exneriment "Hvdroeen Atom Spekrum Using a n AA Spec&ophotometer" Gas bien described bv J. Douelas and his colleaeues - IJ. . Chem. Educ. 1987, 64, 5521. ~ h e i eauthors explain the emission of the Balmer series and propose four original questions to be answered by the students. I would like to point out two observations with regard t o this article.
790
Journal of Chemical Education
We wish to thank your reader for bringing t o our attention Hollenberg's work published two decades ago. While our experiment involves the AA spectrophotometer and the aproach we Dosed to the students is different. we certainlv would havheferenced Hollenberg's work if i t had not eluded us, because, in retrospect, our work is derivative of his.
J. Douglas and E. I. von Nagy-Felsobukl UnlversiPfof Newmtle New SoUm Wales. 2308 Ausbalia
