342
ANALYTICAL
obtained by means of an adequate dilution to an intermediate aromatic content (Table VII, tests 13 to 19). There is another source of abnormality when the relation between the molecular weight of the aromatics with respect to that of the nonaromatics is too high. In this case absorptions higher than the actual aromatic content may be found (Table VII, tests 46 and 47, and Table VIII, tests 13, 14, and 17). When that relation is too low, absorptions lower than the actual aromatic content may be found (Table VIII, tests 35 to 37). However, there is always a wide zone of that molecular weight relation in which the results are correct (Table VII, tests 48 to 53, and Table VIII, tests 1 to 5, 7 to 12, 20 to 25, and 27 to 29). This shows the experimental basis for the recommendation to correct the molecular weight relation by means of an adequate
dilution. In the statistical balance of this method with pure hydrocarbon mixtures, covering 65 comparisons, 42 of them (65%) were within an error of ±0.5%; 80% of the comparisons were within ±1.0% and if one goes as high as ±2.0% it is possible to include practically all the samples (95%). These figures become more significant when one realizes that the error covering 50% of the samples is the probable error of a method and the error covering 68.3% of the samples is the mean square error or standard deviation of a method. These must be taken preferably as reasonable limits of
apart from some individual deviations. The standard deviation of this method can be estimated within ±0.6%. In the cases studied the agreement of this method with pure hydrocarbons is better than its agreement with the IP and ASTM methods. This may indicate a better accuracy for the proposed method than for the latter two. error
ACKNOW LEDGM ENT
The author wishes to acknowledge the encouragement of A. J. Zanetta and J. E. Vinai; the careful work of A. Dubin in many comparisons with the IP method; the efficient help of P. EL-Juri and R. Castro; the careful work of C. D. Bizzozero, A. Nieto, and C. Mamberti from Florencio Varela Research Laboratories in the comparisons of this method, especially with the ASTM method; and to thank A. Seoane and O.
CHEMISTRY
Alonso for drawing the figures; J. E. Simmons for the English version; and S. S. Kurtz, Jr., Sun Oil Co., for his helpful suggestions that contributed to the present form of this paper. LITERATURE
CITED
(1) Am. Soc. Testing Materials, Method D 483-40 (1949). (2) Am. Soc. Testing Materials, Tentative Method D 875-46T
(1949). (3) Am. Soc. Testing Materials, Tentative Method D 155-45T (1949). (4) Am. Soc. Testing Materials, Tentative Method D 1017-47 (1949). (5) Bennasar, J., and Rikles, B., “Apuntes sobre Destilación del Petróleo," Vol. I, pp. 153-4, Buenos Aires, BIP (Yacimientos Petrolíferos Fiscales), 1938. (6) Berg, C., and Parker, F. D., Anal. Chem., 20, 456 (1948). (7) Conrad, A. L„ Ibid., 20, 725 (1948). (8) Cosciug, Timothei, Petroleum Z., 31, 5-7 (1935). (9) Ellis, C., “The Chemistry of Petroleum Derivatives," Vol. II, p. 30, New York, Reinhold Publishing Corp., 1937. (10) Ibid., p.1155. (11) Gambrill, C. M., and Martin, K. B., Ind. Eng. Chem., Anal. Ed., 18,689 (1946). (12) Godlewicz, M„ Nature, 764,1132 (1949). (13) Heigl, J., Black, J., and Dudenbostel, B., Anal. Chem., 21, 554 (1949). (14) Huntress, E. H., and Mulliken, S. P., “Identification of Pure Organic Compounds," pp. 496-519, New York, John Wiley & Sons, 1941. (15) Institute of Petroleum (London), Method IP 3/42 (1946). (16) Jones, H. O., and Wootton, H. A., J. Chem. Soc., 91, 1146 (1907). (17) Lipkin, M. R., Hoffecker, W. A., Martin, C. C., and Ledley, R. E., Anal. Chem., 20, 130 (1948). (18) Mills, I. W„ Kurtz, S. S„ Jr., Heyn, H. A., and Lipkin, M. R„ Ibid., 20, 333 (1948). (19) Sachanen, A. N., “The Chemical Constituents of Petroleum,” p. 136, New York, Reinhold Publishing Corp., 1945. (20) Ibid., pp. 155-6. (21) Spakowsky, A. E., Evans, A., and Hibbard, R. R., Anal.
Chem., 22,1419(1950).
(22) Watson, K., and Nelson, E. F., Ind. Eng. Chem., 25, 880 (1933).
Received for review April 3, 1952. Accepted July 31, 1953. Presented at the First South American Petroleum Meeting, Montevideo, Uruguay, March, 1951.
Pyrohydrolysis in the Determination of Fluoride and Other Halides JAMES C. WARE1, W. D. CLINE1, and RUTH D. TEVEBAUGH3 Institute for Atomic Research and Department of Chemistry, Iowa State College, Ames, Iowa preparation of large quantities of uranium(IV) fluoride
and thorium fluoride by hydrofluorination of the oxides, in THE
the Manhattan Project during the years 1942-1945, necessitated rapid and accurate analytical method for determining these and other halides. Various modifications of the fluosilicic acid distillation technique of Willard and Winter (23) were in use, but these were time consuming, especially with fluorides produced at high temperature, and other methods (12) were not promising. A method based on reversal of the preparative reaction of the (^qorides was developed, and proved highly satisfactory and versatifSfl·) t3-l?e method consisted essentially of passing a current of 9Y6F {the fluoride in a platinum apparatus at a high tem.,p$r%|i^K,|oJJpjv(j
