do not appear in the successor text "Chemical Principles" by Dickerson, Gray, and Haight [W. A. Benjamin, 19701. Denis Quane Converting Spectral Line Wldths To the Editor: In the article "Converting Atomic Spectral Line Widths from Frequency to Wavelength" [54,615, (197711 the authors comment on the relative correctness of two formulas. They conclude that the expression Ad2
Ah=-Au
"
is more correct than
They point out that the latter is obtained by differentiation, but do not point out that it is thus strictly valid only in the limit of zero line width. It is the replacement of a differential quantity by a finite difference that is the source of any errors. Further.. thev . concern themselves overly with the minus signs in the expressions, instead ofsimply saying t h ~ thc t line is iust as wide from left to richt as it is from right to left. i hope that these comments may serve to simplify some of the points made in an otherwise quite interesting paper. Oliver G. Ludwig
East Texas State University Commerce, 75428
Perchlorate Hazard To the Editor: I read with interest the article hv H. R. Hunt. Jr.. in the November issue of the Journal of chemical ducati ion. The ,qticle describes the preparation of d-C0(phen)3~+,the deof its optical rotation, and its precipitation and isolation as the perchlorate salt. It is incredible to me that, despite the ever-increasing number of devastating explosions which result from the use of the perchlorate anion, experiments designed for freshman lahoratory still incorporate its use. I am surprised that the referees of this article were not more critical on this point. Granted that perchlorate salts of most cobalt((II1) complexes are relatively safe, i t nevertheless seem obvious that to &low even the smallest opportunity for explosion in the freshman lahoratory is foolish. There are other "large" anions (BF;, PF;, tetraphenylborate) which are equally as suitable as ClOa for the precipitation of metal comnlexes: surelv one of these could have been used in this experiment. I do not think that this Journal should lend imnlicit suonort to the use of daneerous materials in the freshman laboratory by publication of articles such as this, particularly in those cases where elimination of the hazardous aspect(s) is easily accomplished. ~
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Villanova University Villanova. Pennsvlvsnia 19085 To the Editor: Professor Ludwig is, of course, correct in hisstatement that the true differential is defined in the limit of zero line width. We welcome his added clarification to our discussion. Our approach was based on visualization, which is difficult to achieve in the calculus. We feel the mention of this limit is of value, although realistically the limit is unattainable. The fact that the line width normally is very close to zero (comparatively) is the major rationalization for using thedifferential form in the first place. Professor Ludwig is explicitly stating the mathematical reason for the results stated in the paper. Regarding the minus sign, we are not convinced we overemphasized the explanation. The minus sign is not explicit (is i t -X2. or -12.or -AV?). The students we have known do not make the immediate assumption that just because the line is the anme width thxn right to left or left to right, the sign c m ~he dropped. Further claiification is necessary. ~
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M. L. Parsons R. J. Lovett Arizona State University Tempe, 85281 Frost Diagrams To the Editor: In their interestine DaDer on oxidation state diagrams, Friedel and Murray 1.i. CHKM.EDUC.,Li,48S (1977,l ltst a numher of Hritish trxthooks which use this method of presenting inorganic thermodynamic data. They remark that such diagrams seem to have not been used in American texts. In fact, a t least one American textbook has made use of Frost diagrams, and a t a more elementary level than the British texts cited by Friedel and Murray. Gray and Haight in "Basic Principles of Chemistry" IW. A. Benjamin, New York, 19671, make extensive use of these diagramsin their treatment of the chemistry of non-metals. Apparently this teaching idea did not meetaith an enthusiastic respoise, since Frost diagrams 476 1 Journal of Chemical Education
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Nicholas K. Kildahl Worcester Polytechnic Institute Worcester. Massachusetts 01609 To the Editor:
Professor Kildahl's criticism of the use of the perchlorate ion in my General Chemistry experiment [54,710 (1977)]appears to have some merit. and I reeret that I did not include in the manuseriot a warnine conceking the"possib1e explosion hazard. After reading prof. ~ildahl< comments I have heated and pounded small samples of the Co(phen)~(CIO&product without explasive result, but the material will burn if ignited. These observations suggest that the hazard is minimal under the experimental conditions described, but it would neverthe-less be prudent to handle the product with caution. The substitution of a different large anion for perchlarate is a good sueeestion. but consideration of oossible substitutes indicates that
13- ions appeared to me to he the most promising, but the former proved to he unsatisfactory because of incomplete precipitation of the complex, and the latter is unsatisfactory because of its low stability, and because its color interferes with
