DECEMBER 15. 1940
ANALYTICAL EDITION
767
Solid Substances
Literature Cited
The specific gravity of solids is important in the field of mineralogy and in investigations of crystalline structure and molecular weight; very little emphasis is placed on its determination in any of the known schemes of qualitative organic analysis. The most suitable procedure for small crystal fragments is the flotation method of Retgers (26) n hich by including centrifugation has been improved by Hendritks and Jefferson ( 2 2 ) and by Bernal and Crowfoot (10). The latter method has been tested in this laboratory, applying carbon tetrachloride, benzene, nitrobenzene, Clerici solutions, bromoform, and methylene iodide in their pure forms or in mixtures. After centrifuging for 5 minutes, the specific grayities of the reference liquids in which the crystals remained suspended v e r e determined. The amount of material necessary varied over a wide range, between 50 and 250 micrograms, and the accuracy of the determinations was about 5 p. p. t., depending on the accuracy with a h i c h the specific gravity of the reference liquid was determined. Since the volumes of the latter after the separation from the solid phase were between 10 and 100 cu. mm., centigram and milligram pipets were applied. Benzoic acid, naphthalene, and resorcinol gave results which agreed favorably n ith the values reported by Hendricks and Jefferson ( 2 2 ) .
(1) Alber, H. K., IND. ENG.CHEM., Anal. Ed., 10, 348 (1938). (2) Alber, H. K., J . F r a n k l i n I n s t . , 226, 813 (1938). (3) Slber, H. K., “Microtechniques for the Purification of Organic Compounds”, Cincinnati Meeting, American Chemical Society, April, 1940. (4) Alber, H . K., 2. anal. Chem., 90, h i (1932). (5) Alber, H. K., and Batt, TT. G., Milwaukee Meeting. Anierlcan Chemical Society, September. 1935; abstracted in Mikrochemie, 25, 392 (1939). (6) Alber, H. K., and Biyant, J. T., ISD. ESG. CHEM., Anal. Ed., 12. 305 (19401. (7) Alber, H. K., and Harand, J., J . Franklin Inst., 224, 729 (1937); McDonald, E., Ibid., 225, 166 (1938). (8) Alber, H. K., and von Kenzenberg, 11 , Z . anal. Chem., 84, 114 (1931). (9) Batt, W.G., and Alber, H. K., in press. (10) Bernal, J. D., and Crowfoot, D., Satzire, 134, 809 (1934); 135, 306 (1935). (11) Beutler, R., Mikrochemie, 16, 133 (1936). (12) Blank, E. W., and Willard, 31. L., J . Chem. Education, 10, 109, (1933). (13) Browning, B. L., private comniunication; Tech. Assoc. Papers, 20, 311 (1937); Paper Trade J., 105, No. 10, 38 (1937). (14) Ciochina, J.,2.anal. Chem., 107, 108 (1936). (15) Clemo, G. R., and McQuillen, A , , J . Chem. SOC.,1935, 1220. (16) Collander, R., Protoplasma, 8, 440 (1929). (17) Dermer, V. H., and Dermer, 0. C., J . Am. Chem. SOC.,59, 1148 (1937). (18) Emich, F., and Schneider, F., “Microchemical Laboratory Manual”, pp. 40 ff., New York, John Wiley & Sons, 1932. (19) Flaschentraeger, B., Z. angew. Chem., 39, 717 (1926). (20) Francis, L. D., J . Lab. Clin. Med., 22, 718 (1937). (21) Furter, M., H e h . Chim. .4cta, 21, 1666, 1680 (1938). (22) Hendricks, S.B.. and Jefferson, 32. E., J . Optical SOC.Am., 23, 299 (1933). (23) McLean, A . , and Adams, R . , J . Am. Chem. SOC.,58, 804 (1936). (24) Mouquin, H., and illber, H. K., Pittsburgh Meeting, American Chemical Society, September, 1936; abstracted in Mikrochemie, 21, 142 (1936). (25) Retgers, J. W., S e u e s Jahrbuch Mineralogic, 1889, (2) 185; 2. physik. Chem., 3, 298, 497 (1889). (26) Roth, H., and Daw, E. B., “Quantitative Organic Microanalysis of Fritz Pregl”, pp. 250, 254, Philadelphia, P. Blakiston’s Son and Co., 1937. (27) Struszynski, M., Przemysi Chem., 20, 51 (1936).
Conclusion The general applicability of decigram, centigram, and milligram pipets has been demonstrated for the determination of specific gravities of liquids and solids. The accuracies obtainable under ordinary laboratory conditions are sufficiently high for a safe identification of unknown liquids or solid organic compounds in qualitative organic microanalysis, as shown by their satisfactory use over more than 5 years by different investigators.
Acknowledgment The author nishes to express his gratitude to IT. G. B a t t for his help and suggestions during the preparation of this article.
PRESEXTED before the Division of \Iicroclieinistry a t t h e 96th Meeting of t h e American Chemical Society, IIilwaukee. Wis.
Correspondence-Toxicity of Aromatics SIR: Apparently the degree of toxicity of the simpler members of the aromatic series is a subject more involved than we recognized when preparing the article entitled “Detection of Aromatics in Air” [IND. ENG.CHEM.,Anal. Ed., 12, 433 (1940)]. In this article we made the unfortunate error of substituting the word “aromatic” for “benzene” in quoting the Xational Safety Council Benzol Report of 1926. R. C. Stratton, supervising chemical engineer of the Travelers’ Insurance Company, has very kindly pointed out that this error has caused the reproduction of an inaccurate statement: “that 100 p. p. m. of aromatics is the maximum aromatic concentration in which a man may rvork safely.” The original of this quotation, we now understand, meant that concentrations of benzene in excess of 100 p. p. m. will cause chronic, but not acute, pathological poisoning. Although a nurnber of references in Ethel Browning’s “Toxicity of Industrial Solvents”, issued by His Majesty’s Stationery Office, London, 1937, state that toluene and xylene are a t least as toxic as, if not more than, benzrnc, M r . Stratton has explained that these statements
refer to acute poisoning, and most probsbly indicate that these heavier aromatics cause more rapid narcosis, and other symptoms of acute asphyxiation or poisoning, than does benzene. Mr. Stratton points out a further reference, which we had overlooked, as follows: “With concentrations of 620 to 1000 p. p. m., inhaltttion of toluene produces practically no symptoms in animals.” Our article was concerned primarily with a procedure for determining quantitatively the concentration of aromatic vapors in industrial atmospheres and we believe that the method outlined is accurate, reproducible, and valid for this purpose. The decision as to the maximum concentration for a satisfactory working condition does not rest with the chemist, and is apparently a potential subject for wider investigation and education. We are offering this conimunication to correct any inaccurate impressions which may have been made by the original article.
G. R. GILBERT AXD R. E. TAIWICH HUMBLEOIL & REFININQ Co BAYTOWN, TEXA0
October 21, 1940
