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Laboratory Hazard
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Sir: A 4-L, capped Winchester glass bottle of freshly prepared solution containing ammonium peroxydisulfate in 98% sulfuric acid recently ex ploded while being stored in an acid cabinet under a fumehood at the University of Calgary. This solution has been suggested as an alternative to chromic acid baths (Anal. Chem. 1982, 54, 1456 A). From the above incident it is assumed that the solution has a tendency to gas and build up pressure in closed containers, and therefore must never be stored in enclosed containers. Due to the extremely dangerous properties of this solution, the read ers should be cautioned on the stor age of this solution. It is recom mended t h a t plastic polypropylene tanks which are loosely covered and vented be used. P. S. Surdhar Chemical Safety Supervisor University of Calgary 2500 University Drive, N.W. Calgary, Alberta, Canada T2N 1N4
Classical Analysis Sir: The REPORT by Charles M. Beck II, "Classical Analysis: A Look at the Past, Present, and Future" (Anal. Chem. 1991, 63, 993 A), was a plea
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310 A · ANALYTICAL CHEMISTRY, VOL. 64, NO. 5, MARCH 1, 1992
sure to read. We would like to offer a comment on the work of J. Kjeldahl published in Fresenius' Z. f. Analytische Chemie 1883, 22, 366, cited on p. 997 A. He did indeed distill the ammonia, released by digestion, into standard sulfuric acid. But the back titrant used was not sodium hydroxide. It was sodium thiosulfate. Kjeldahl stated: " . . . I would like to recom mend a method that is almost always used by me. The method is old, erro neously half forgotten, because it has precision and ease of performance. It depends on the well known reaction: A mixture of potassium iodate and potassium iodide releases an iodine equivalent for each acid equivalent added, which can then be titrated with sodium sulfite." For stability he recommended sodium thiosulfate. Potassium iodide and potassium io date were added before titration. The blue starch end point, he noted, could be as easily determined by lamplight as by daylight. This could not have been said for methyl red and titra tion with sodium hydroxide, consid ering the electric lamps of that year. This was an outstanding utilization of knowledge of chemistry to accom modate the hardware of the time. M. Truett Garrett, Jr. J o h n F. Stehlik Public Utilities Department City of Houston P.O. Box 1562 Houston, TX 77251-1562
