For the last entry the rate constant for inside radon emigration is 20 times that of radon decay, or the half-life for emieration is 1/20 that of decav or 0.19 dav. In this case onlj'5q of the maximum potential radloacti;ity ol'a sealed home in obtamed. and the half-time for reachine that 5'; is 0.18 day or about 4.4 h. Thus the more extensive the leaks. the lower the amount of radioactivity, and also the more rapidly the steady state radioactivity level is achieved. The outcome from this analysis is that in a leaky home the maximum potential radioactivity is much higher than that measured under typical use. The leakier the conditions under which the radioactivity measurements are made, the greater this difference. As practical advice, when returning from vacation to a closed, radon-susceptible home, air the home immediately.
Literature Cited 1.Scott, T M. J. Chem Edvr 1981.68.950. 2.Aldrieh Cato1og:Alddch Chemical: Milwakee, 1990; p 930. 3Aldrich Cofolog.Aldrich Chernicak Mlwsukee, 1990; p 1326.
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R. Bruce Martin
University of Virginia Chariottesville, VA 22903 Solubility Data on BButanol
To the Editor:
In connection with the article "The Water Solubility of 2-Butanol: A Widespread Error" (I)in the Tertbook Forum column, I would like to bring to the attention of readers of the Journal of Chemical Education the "Solubility Data Series" compiled by the International Union of Pure and Amlied Chemistrv. which orovides critical evaluations based on compreh&sive cokpilations of primary publications. includine Volume 15. Alcohols with Water (2). In this voln&e, a see'tion prepared by G. T. Hefter provides a "best" value of 18.1 f 0.8 e 2-hutanoll100 e aaueous solurecent retion a t 298 K and a full &tical account. sults for this particular system were published by G. T. Hefter, A. F. M. Barton and (the late) A. Chand in(3). The "Solubility Data Series" is now providing the definitive compilation of solubility information for all types of svstems (involving eases. solids and liauids) and should be drought to the atGGtion of all scientists.
ore
Literature Cited 1. Alger, D. B. J. Chem.Edue. 1981.68. 939. 2. Heller, G. T. In Almhds vilh W o w Baton, A. F M.. Ed.: IUPAC Solubility Data Series, Vol. 15; Pergamon: Oaf&, 1984. 3. Hefer, G.T.; BaMn, A. F M.; Chand, k J Chem Soc. For+ l h n s 1981,87(0,
591.
Allan Barton
School of Mathematics and Physical Sciences Murdoch University Perth, Western Australia 6150 Mineral Spirit as a Halogen Extraction Solvent
To the Editor:
T. M. Scott's ( I ) excellent suggestion that mineral oil be used instead of chlorinated solvents to extract halogens can be improved. After reading his paper, it occurred to us that mineral spirit would be more pleasant and more convenient to use because of its lower viscosity. The "mineral spirits" sold by Aldrich (2) worked well, and separated in 10 s. instead of the 20 s re~ortedbv Scott for mineral oil. I t is also cheaper. Its flash ooint (2)is 57 'C. nearlv the same as the 60 'C for undecaie t3,, there is iittle danger of fire. In confirmine this. we found that if a liehted match is droooed into it. th;? match sinks and the fiquid extinguishis' it. If t h i liehted match is d r o ~ ~into e d a ~ o othat l is shallow enoueh tcat the match canddt sink and continues to bum, the ll'quid takes fire after about ten seconds. Presumably this is the time necessary to warm the liquid to the flash point. This level of fire risk is low enough to be acceptable.
DeanJohnson Stephen Hawkes
Oregon State University Co~allis,OR 97331-4003 Finding the Elusive Benzene Tree
To the Editor:
Several German-speaking readers have expressed puzzlement to me after trying to track down the German orig. inal of A. W. Hofmann's delightful speech in honor of Kekul6 in 1890 (11. Their puzzlement is due to the fact that two mistakes crept into our reference to the Zeitschrift fir Farben- und Textil-Chemiefrom which the translation was made. Firstly, this journal was unfortunately abbreviated a t the suh-editing stage into the later (1904) title of the journal's continuation, namely Zeitschrift fur Farben- und 'Rxtil-Industrie; i.e., Z. Farben Tat. Ind. Inevitably this has made it difficult for German readers to track down the first volume of this rare iournal. A second confusion has arisen over the of Schultz's article, which should have read DD 231-233 not DD 1-2. The Xerox c o ~ v of Schultz's paper'from which our translation was marie, and which was kindly supplied by Susanna Rudofsky, t u r n s out to have been a repaginated offprint (Sonderabdruck), which was supplied by the journal's printer for Schultz to send to friends and colleagues. The copy from which the translation was made, which is identical in all other respects with pp 231-233 of the Zeitschrift, is to be found in the Urkunden- und Handschriften-Sammlung of the Deutches Museum in Munich, file 1568 SchultzICaro. Our apologies to German readers for this confusion. Literature Cited
1. B m k , W. H.;Benfey, 0.T:Stark,S."Hofrnan"'aBenzeneTree". J Ckam Edue 1981, 68.881-888. William H. Brock Department of History University of Leicester Leicester LEI 7RH, Engiand,UK VSEPR Theory and Magnetic Molecular Models
To the Editor:
The two ingenious two-dimensional "Overhead Projection Demonstrations" by Shaw and Shaw and by Hervas and Silverman IJ. Chem. Educ. 1991., 68.. 8611.testifv to a continuing interest in a fundamental topic in introductory chemistry courses, viz., Gillespie and Nyholm's valence shell electron pair repulsion (VSEPR)theory for predicting the shapes of simple molecules. This JournaZ's readers may be interested in a set of three-dimensional molecular models easilv constructed from mamets and Stvrofoam spheres basid on the simple electrostatic princLple that electrons, because they have the same charge, naturally repel one another [Kaufiinan, G. B. Chemistry 1975,48(9), 61. Knowledge of atomic or molecular orbitals is not required; only the total number of valence electron pairs, both shared and unshared, surrounding the central atom in the molecule, must be known. This is readily obtained from the atomic numbers or periodic group numbers of the atoms involved. George B. Kaufhnan
CaliforniaState Univenity, Fresno Fresno, CA 93740 Volume 70 Number 12 December 1993
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