To the Editor: The Lyles are certainly correct. I take full responsibility for the error in our text; your readers might like to know that Bob Schuetz is in fact a first-rate sailor, having participated for years in the annual Mackinac Straits races on Lake Michigan. W. H. Reusch of our Department tells me that nautical terms have also been used for the port and starboard hydrogens in boat cyclohexane, Be and Ba in the Lyle nomenclature being referred t o as the gunwale (gunnel) and keel (g and k ) hydrogens, respectively. Harold H a r t Michigan State University East Lansing, Michigan 48825
the current is switched off the oxygen immediately drops from the magnet. Liquid nitrogen when poured between the poles is completely unaffected. Sufficient liquid oxygen (10 cm3 for a single demonstration) can be obtained conveniently by passing a slow stream of oxygen through a trap cooled in liquid nitrogen. We use the magnet of our Gouy Balance (Newport Instruments Ltd., U.K.) with a 1 cm gap and a field strength of about 5000 gauss; this holds the liquid oxygen firmly between the poles. Although we have never had any problems in the handling of the small quantities of liquid oxygen used in this experiment, attention is drawn to the dangers involved in handling liquid oxygen [J. CHEM. EDUC., 45, A547 (1968)l.
J. W. Lethbridge M. B. Davies
Sensitive CN Test
To the Editor: A recent article in this Journal [50, 72 (1973)l recommended that the sodium fusion procedure for the detection of certain elements in qualitative organic analysis he replaced by the calcium oxide-zinc fusion technique. Convenience, safety, and less uncertainty in the test for nitrogen were the underlying reasons given for recommending this replacement. Admittedlv. - . the commonlv used Pmssian blue test for nitrogen (as cyanide) does leave much to he desired with its nroloneed hoiline. -. acidification. and expulsion of interferkg compounds. However, a recent discovery by Guilbault and Kramer [Anal. Chem., 38, 834 (196611 which utilizes o-dinitrobenzene and p-nitrobenzaldehyde is a magnificently sensitive and selective test for cyanide. In the past five years of using this new procedure for nitrogen, we have achieved over 95% success in this once difficult test. Another excellent feature of this test is that one drop of stock solution can he used directly in a spot plate with no need for p H adjustment or heating. The authors of the calcium oxide-zinc fusion article indicated that they were unable to detect nitrogen in a sample of hemoglobin. I was able to get a strong test for nitrogen from hemoglobin using the dinitrobeniene-nitrohenzaldehyde procedure following sodium fusion. Even isatin gave me a positive nitrogen test, a compound that might well be more difficult than hemoglohin. A second reason for not supporting the proposed calcium oxide-zinc fusion is the complete omission of any mention of fluoride detection. Perhaps the formation of insoluble CaFz would render fluoride detection quite difficult if not impossible. The presence of this halogen can readily he determined following a sodium fusion. Perhaps the calcium oxide-zinc method is safer than running a sodium fusion. However, in 15 yr of organic chemiatn. laboratory work d u r ~ n gwhich time I carried uut or observed over 1>00 sodium fusions on the semimicro scale, not one accident has occurred. Thomas McCullough, CSC St. Edward's University Austin, Texas 78704
The Paramagnetism of Oz To the Editor We noted with interest in this Journal, details of an experimental demonstration of the paramagnetism of Oz (50, 217 (197311. This article prompts us to mention a simple hut more spectacular demonstration of the same effect which we use. Liquid oxygen readily bridges the pole pieces of an electromagnet when poured between them. When 656 1 Journal of Chemical Education
Stockport College of Technology Wellington Road South Stockport SKI 3UQ,England Daily Methionine Requirements To the Editor: I would like to call your attention to an error in the article by Leh and Chan on sulfur compounds that appeared in the April issue (50, 246 (1973)). Table 3 showing daily methionine requirements is incorrectly labelled. It should be as follows Subject infants Il-year-old boys young men young women Readers who believed that they must eat over 70 g of methionine per day should now be reassured. Kenneth Sumner Bridgewater State College Bridgewater, Massachusetts 02324 Experiment Using Potassium Trioxalatoferrate(llI) Trihydrate To the Editor: This is a comrneni on ".in Experment Sequence Invol\.ing Porasaium 'l'rioxalatuferrate~llli 'l'rihvdrate" 1I)avid W. Bnx~ks.-1. C H E l I . E1)UC.., 50.. 218 1197311. .. We have used the same compound in a somewhat different sequence. Students prepare samples with the Hz02 method and crystallize them. The samples are dehydrated in drying ovens (llO0C, 1 wk). The iron content is determined by titration with sodium hydroxide to a phenolphthalein end point (1 g KzFe(CzOa)a in 100 ml, titrate three 10-ml samples with 0.03 M NaOH, 24 ml each). The end point is obscured somewhat by the precipitation of rust hut can be seen well enough by the students. The precipitate coagulates shortly before the end point. The potassium content is determined by an ion-exchange method. About 30 ml of the solution mentioned above is run through a cation-exchange resin ( H + form, discard 10 ml, then titrate three 5-ml samples with 0.03 M NaOH, 25 ml each). The titration now requires 6 mole O H per mole of complex. ~
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Carl F. Aten, Jr. Hobart and William Smith Colleges Geneva, New York 14456
