Safety Warning: Unwntrolled Reaction To the Editor:
An experimental procedure puhlished recently [J. Chern. Educ. 1987,64,188] has lead to a potentially serious accident. The procedure calls for adding concentrated nitric acid to gasoline to extract the lead for atomic absorption assay. Following the directions, the acid was added in one portion at room temperature. After a short induction period one of the samples spontaneously boiled over, emitting copious hrown fumes. Shortly thereafter, a second sample followed suit. The third sample did not react. The puhlished procedure calls for the use of separatory funnels. Fortunately, we had substituted Erlenmeyer flasks and avoided injury to the students. The gasoline contained 10% ethanol. Tests with synthetic mixtures of isooctane and ethanol reacted the same way. In our hands, commercial gasoline without alcohol behaved safely. Gasohol must not be used in this experiment. David H. Smith
Sodium hydrosulfite is also used to remove traces of oxygen from gases such as nitrogen or argon when it is desirable to render them absolutely oxygen-free. A solution of 2 g of sodium anthraquinone-2-sulfonate and 15 g of sodium hydrosulfite in 100 mL of 20% aqueous potassium hydroxide affordsa blood-red solution of the diradical dianion (Fieser's solution). This mixture will remove about 800 mL of oxygen. The color fades and the solution turns brown when it is exhausted. According to Cotton and Wilkinson (Advanced Inorganic Chemistry, 2nd ed.; Interscience: New York, 1966; pp 551552), the dithionite dianion has an eclipsed conformation and an unusually long (2.89A) and, therefore, weak, S-S bond (the normal lengthis 2-2.15A). It is in equilibrium with the radical anion, SzOa2-* 2 SOz- and is therefore a powerful and rapid reducing agent.
Dome College Crete, NE 68333
Kenneth L. Williamson Mount Holyoke College South Hadley, MA 01075
Reduction ot indigo: Sodlum Hydrosulflte as a Reducing Agent To the Editoc
In the article "An Indigo Plant as a Teaching Material" [1987,64,332]the procedure for the reduction of indigo calls for "one liter of water containing 30 g of sodium hydrogen sulfite and 30 g of sodium carbonate.. ." The confusion between sodium hydrogen sulfite (NaHS03, sodium hisulfite) and sodium hydrosulfite (NazSzOJ is a common one, even to those whose native language is English. We have found it necessary to place warning labels on the stockroom shelves and on bottles of both reagents to alleviate the confusion. Even purchasing the reagent can he confusing. Fluka calla it sodium hyposulfite, Aldrich and Fisher sodium hydrosulfite, and Baker, VWR, and Alfa sodium dithionite. Fortunately mixing up the two reagents on a microscale is usually not hazardous, although sodium hydrosulfite is listed in the Aldrich catalog as a flammable solid. Sodium hydrosulfite, sodium dithionite, NazSz04, is an inexpensive and versatile reducing agent. In Microscale OrganicExperirnents (Williamson,K. L.; D. C. Heath: Lexington, MA, 1987) it isused toreduce 3-nitrophthalhydrazide to 3-aminophthalhydrazide (luminol), Orange I1 to 1,2-napthoquinone in the synthesis of vitamin K1, anthraquinone to anthrone, Martius Yellow to 2,4-diamino-1-naphthol, and, of course, indigo to its leuco form. 0-NHq-
Another Vlew of the Vlslble Spectrum To the Editor:
A recent article [1987,64,627] descrihes the construction of a paper device that can he used with a Spectronic 20 to view the visible spectrum. The idea is not mine, but the same results can he achieved by using a piece of ordinary classroom chalk that has been flattened to provide a 45-degree angle reflecting surface. The chalk fits comfortably into the standard cuvette. E. S. Hanrahan Marshall University Huntington. WV 25701
Hund's Rule-Llke Behavlor among Humans! To the Editor:
Like Scott T. Hills descrihes in his chair demonstration (1987, 64, 271 to illustrate Pauli's exclusion principle and Hund's rule, on my Metro bus ride to work every day, I have consistently observed the naturally occurring phenomenon of Hund's rule-like behavior among humans. Passengers first occupy empty seats singly, if available, before taking a seat next to a seated passenger. If the entering passengers are "coupled" by relationship, however, they do occupy adjacent seats. Parthasarathy Nambi
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1311 W. 44th Terrace X206 Kansas City. MO 641 11 :
Martius Yellow
Volume 66
Number 4
April 1989
359
