INDUSTRIAL AND ENGINEERING CHEMISTRY
402 Table VI. Weight Ratio, Propyl Alcohol to Formaldehyde 5 :1 10: 1 15: 1
Amyl Alcohol to Formaldehyde 2:l 5 :1 1O:l 1OO:l
Table
VII.
Material
Effect of n-Propyl and n - A m y l Alcohols Formaldehyde Added
Formaldehyde Found
Vol. 17, No. 6
ment of this method. Marie Corse and Robert Yale deserve much credit for their faithfulness in applying and proving the value of this method for determining formaldehyde.
Mg.
Mg.
LITERATURE CITED
0.035 0.035 0.035
0.035 0,033 0.033
(1) Blaedel, W. J., and Blacet, F. E., IND.ENG.CHmI., ASAL. ED., 13, 449 (1941). (2) Boyd, M. J., and Logan, M. A,, J . B i d . Chem., 146, 279 (1942).
0.044 0.044 0.044 0.044
0,042 0.037 0.030 0.021
Determination of Formaldehyde in Formals Formaldehyde Formaldehyde Found= Theory
70
(3) Denigks, G., Compt. rend., 150, 529 (1910). (4) Donnally, L. H., IND.ENG.CHEM.,2 ~ 3 . 4 ~ED., . 5, 91 (1933). ( 5 ) Eegriwe, E., 2.w a l . Chem., 110, 22 (1937). (6) Hoffpauir, C. L., Buckaloo, G. W., and Guthrie, J. D., IND. ENG.CHEW.,ANAL. ED., 15, 605 (1943). (7) Yoe, J. H., and Reid, L. C., Ibid., 13,238 (1941). PRESEXTED before the Division of Analytical and Micro Chemistry a t the lOSth Meeting of the AMERICAN CHEMICAL QOCIETY, New York, N. Y.
70
36.4 36.9 Methylal (7.370 methanol) 37.50 37.5 Pentaerythritol diformal 20.2 20.27 Pentaerythritol monoformal 20.00 21.2 Pi eronal 19.7 22.6 n - h o w l formalb 100.0 102 Trioxane No free formaldehyde found in a n y of these samples. Purity not known. B y the 2,4-dinitrophenylhydra$ne procedure, 19.9% formaldehyde was found.
*
very small amounts (0.02%) of formaldehyde can be determined in the presence of this aromatic aldehyde and probably in the presence of other aromatic aldehydes. Acetone, while i t does not give a color with chromotropic acid, causes the purple color due to formaldehyde to fade when the solution is diluted with water. However, this interference can be eliminated by diluting the solution to 50 ml. with 18 N sulfuric acid instead of water. As little as 1 part of formaldehyde in 5000 parts of acetone can be accurately determined by this modification. Diacetone alcohol and methyl ethyl ketone interfere very markedly with the development of the formaldehyde color. I n the presence of 200 mg. of each of these materials, 0.04 mg. of formaldehyde could not be detected. The mechanism of the reaction between formaldehyde and chromotropic acid has not been investigated. For this reason, no explanation can be offered to account for the various interferences mentioned. RESULTS AND APPLICATIONS
The method described in this paper can be used to determine free formaldehyde or combined formaldehyde which is liberated by acid hydrolysis. Various formals which were subjected to the recommended procedure Rere quantitatively hydrolyzed. Some of the result‘s are tabulated in Table VII. Several dilute formaldehyde solutions which were standardized by the bisulfite-iodine method (4) and by the dimedone method ( 7 ) were analyzed by the chromotropic acid procedure. The agreement was within 3%. Although all spectrophotometric readings were made with a Beckman Quartz Spectrophotometer, there is no apparent reason why a photometer with a filter having a maximum transmittance at about 570 mp could not be used. I n view of the stability of the purple color, it seems likely that a t least semiquantitative results could be obtained by matching the colors of unknowns visually with standards prepared in the same way. The standards would not have to be prepared more than once a week. The method described in this paper is rapid and accurate. As little as 1 microgram of formaldehyde in 1 ml. of solution can be detected. Accuracy of the method is certainly well within 5%. ACKNOWLEDGMENT
The authors wish to acknowledge their indebtedness to T. R. Aalto for his encouragement and criticism during the develop-
BOOK REVIEW The Amino Acid Composition of Proteins and Foods. R. J . Block and Diana Bolling. 396 pages. Charles C. Thomas, Springfield, Ill., 1945. Price, $6.50.
The recent pronounced increase in amount of research attention paid to proteins and amino acids, particularly with respect to the roles they play in nutrition, makes this book timely. No previous text or reference book contains in such detail the published amino acid analyses of proteins and foods. In addition, the authors have rendered a distinct service by outlining and discussing in detail the methods used for the determination of amino acids. The first eight chapters-Diamino Acids, Aromatic Amino Acids, Sulfur-Containing Amino dcids, A-Hydroxy Amino Acids, “Leucines”, Dicarboxylic Amino Acids, Glycine and Alanine, and Proline and Hydroxyproline-contain the available information on methods of estimation and occurrence. In many cases sufficient detail is included, so that the determinations can be made without reference to the original papers. The authors suggest which methods are most reliable and comment pertinently on the various alternate procedures. The tables are extensive and inclu’sive and contain many hitherto unpublished analyses. .-ilthough many of the data are entirely unreliable and of historical interest only, they should make extensive early literature searches unnecessary for future workers in this field. The authors indicate which of the analytical results they consider to be the closest approximations to true values. I t is unfortunate, although doubtless unavoidable, that the references are complete only through part of 1943. Inasmuch as a considerable number of important papers dealing with amino acid methods and analyses have appeared since then, the most acceptable results for the more difficultly determinable amino acids in many cases are now no longer the same as those included in the tables. In particular, data obtained by microbiological methods have required some revision of previous data on the amino acid composition of proteins and foods. Chapter IX describes general methods for the hydrolysis of proteins, the separation and determination of amino acids, and tests for carbohydrates. Chapter X includes a series of 14 tables of amino acid compositions of proteins. Here the entire amino acid moiety is represented, in contrast to the tables in the previous chapters in which the amino acids are presented individually or in groups of two or three. The three tables in the final chapter on the essential amino acid requirement of man include an estimated annual average per capita consumption of essential amino acids, the daily essential amino acid requirements, and the percentage of optimal daily requirements supplied by 100 grams of proteins from several of the commonest foods. The bibliography of more than 700 references and the author and subject indexes have been carefully prepared and help to make the book a handy manual for ready reference. Protein chemists and those interested in the protein phases of nutrition will use it as such. HAROLD S. OLCOTT
