ANALYTICAL CHEMISTRY The last part of the second sentence in this paragraph and following sentences should read: “so a study waa made of the variation of carbon with depth and position of drilling. The carbon content of the top centers of the blocks were aa much as 0.3% higher than the bottom centers. As a result, the present procedure is to cast a block in a metal mold, and drill the sample from the top through the center of the casting as far aa the drill will go. This procedure gives the most uniform quick sample.” James B. Clow L Sons Coshocton, Ohio
JOHN R. BOYD
Bichromate Reflux Method for Determination of Oxygen Consumed SIR: It would appear that the authors of the above paper [Moore, Kroner, and Ruchhoft, ANAL. CHEM.,21, 953 (1949)) have overlooked the fact that silver is an efficient catalyst for the oxidation of acetic acid by dichromate-sulfuric acid mixtures [see, for example, Nicloux, Compt. rend., 184,890 (1927); Corde bard and Michle, Bull. SOC. chim. France, 43 (i), 97 (1928). In a paper by the writer [Muers, J . SOC.Chem. Ind., 55, 71T (1936)l a method was described for estimating the strength (oxidizability) of dairy effluents containing lactic and acetic acids and ethyl alcohol. In the presence of 0.25% silver sulfate all three substances were quantitatively oxidized under conditions otherwise similar to those used by Moore et al. The experimental work, which was only summarized in the published paper, did not cover all the pure substances examined by Moore et al., but it seem probable that the silver catalyst would have improved their results in most cases where there was a large deviation from the theoretical oxygen consumption. Central Laboratory United Dairies Ltd. London W. 12,England
M. M. MUERB
SIR:We wish to thank Muers for calling our attention to this rapid method for estimating the strength of a solution containing organic matter. Unfortunately, Muers’ procedure was published as a part of a study on the biological purification of whey solutions. The procedure for oxygen consumed used by Muers in this study was not stressed or given in detail; consequently, it was not cross-indexed in Chemical Abstracts. Therefore, in our bibliography search on procedures for oxygen consumed thw particular method was not found. This center has not followed directly studies on the purification of whey wastes and, therefore, we were not familiar with Muers’ work. An examination of Muers’ method indicates that it followed the same general procedure as that used by Ingols in this country. The procedure used by this laboratory is somewhat different in detail. This center is now engaged in a comprehensive comparative study of five procedures for evaluating the oxygen-consumed values of sewages and industrial wastes. In these studies between 50 and 100 replicates of various wastes are being examined by each procedure and statistical analyses are being made on the results, so that the most desirable method can be determined. As soon as Muers’ suggestion was received, Moore and Ludzack of this laboratory undertook an evaluation of the effectiveness of silver sulfate as a catalyst. To date completed studies, using 100 replicates of a large number of wastes, have shown that the procedure suggested by Moore et al. [ANAL.CHEY.,21, 953 (1949)l had advantages over all others. Consequently, the effectiveness of silver was studied by introducing the quantity of silver suggested by Muers in our dichromate reflux method. Ten repli-
cate portions of 18 organic chemicals have been examined to date with this procedure both with and without silver. This preliminary study has shown that the silver sulfate is very effective in catalyzing the more complete oxidation of most of these compounds. The oxidation of compounds, such as castile soap, caproic acid, glutamic acid, acetic acid, lactic acid, butyric acid, 0cresol, furoic acid, and ethyl alcohol, is raised to values between 80 and 98% by the addition of the silver. Chlorobenzene and spirits of turpentine are oxidized to 41.4 to 46.8% of theoretical by the addition of the silver salt. A few compounds, such as benzene, toluene, and pyridine, are apparently not affected by the addition of the silver and show very little, if any, increase in oxidation. Studies on the dichromate method for oxygen consumed with and without the addition of silver will be continued and a report on this work will be prepared in the future. Cooperative work with the American Society for Testing Materials subcommittee on water-borne industrial wastes and the Committee on Standard Methods for the Analysis of Water and Sewage on this method is being carried on. As a representative of both these committees, I again thank you for bringing Muep’ paper to our attention. Public Health Service Federal Security Agency Cincinnati, Ohio
C. C. RUCHHOFT
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Vitamin Methods. Paul Gyo~gy,editor. Vol. I. x 571 pages. Academic Press, Inc., 125 East 23rd St., New York, N. Y., 1950. Price, $10. This book is the first of two volumes which together will constitute a comprehensive treatise on vitamin methods. In the development of the subject matter, the presentation has been built around the variow techniques employed for assays (physical, chemical, microbiological, and animal assays) rather than the various vitamins. In the preparation of Volume I, Gyorgy haa had the assistance of the following collaborators: Eric T. Stiller, Physical Methods; S a d H. Rubin, Chemical Methods; Otto A. Bessey, Microchemical Methods; E4mond E. Snell, Microbiological Methods; Erich Hirschberg, Use of Optical Instruments. Where several alternative methods are available for a given physical, chemical, or biological assay of a vitamin, these are described in sufficient detail to obviate the necessity for consulting the original sources. Where poasible, the most reliable and widely used procedure is indicated. One of the significant features of this volume is the concise and direct approach employed in presenting the various steps involved in the assays. Preceding the actual details of the assay for each vitamin, a section is devoted to the historical development of the analytical procedure. Pertinent explanatory material relating to the application and interpretation of the technique is usually incorporated in this section, rendering such valuable information available without encumbering the actual laboratory directions. Definite statements on accuracy, precision, and limitations are usually presented if available. Certain sections have not included aa much of the more recent literature as might have been possible. Thus, the section on physical methods, with 340 references, discusses only three papers published subsequent to 1946. The book will be of value to workers in various fields concerned with nutritional problems. E.M. BICKOF
