are expected in air, the method is tested a t the 0.03- and 0.1-p.p.m. levels of 3,3‘-diisocyanato-4,4’-dimethylcarbanilide. I n each case approximately 0.25 p.p.m. of tol~ene-2~4-diisocyanateis present in the analyzed mixture. The analytical data are presented in Table 111. Discussion. Table I11 indicates good recovery niay be obtained with synthetic samples a t both 0.03- and 0.1-p.p.m. levels of 3,3’-diisocyanato4,4’-dimethylcarbanilide in the presence of 0.25 p.p.m. of tol~ene-2~4-diisocyanate. Normally no more than 0.1 p.p.m. of the latter should be present in the atmosphere in areas where isocyanate products are being compounded. At the 0.1-p.p.m. carbanilide level, the confidence interval is A0.029 p.p.m. for the average of duplicate determinations a t a 95% probability level (4). The proposed method has been tested intentionally a t the 0.03-p.p.m. carbanilide concentration to determine the reliability of the analytical scheme directly at a concentration appreciably below 0.1 p.p.m. I n a single experiment, duplicate analyses had been made with a sample containing 0.01 p.p.m. of 3,3’diisocyanato - 4,4’ - dimethylcarbanilide in the presence of 0.25 p.p.m. of toluene2,4-diisocyanate; 0.007 and 0.013 p.p.m. of the carbanilide mere recovered, indicating that much below 0.03 p.p.m. the method is subject to appreciable errors n7l1en toluenediisocyanates are present. Traces of moisture present in the air used in the continuous air-toluenediisocyanate mixer previously described, recause lower tol~ene-2~4-diisocyanate covery. To account for the unrecorered toluenediisocganate, the air from the continuous mixer can be analyzed by the ethyl Cellosolve-nitrite-boric acid
method. Approxi,nately 10 to 30% is recovered, calculat cd as the 3,3’-diisocyanato-4,4’-dimetl1ylcarbanilide. An examination of the inside surfaces of the continuous mixer ~liomsthe presence of a fine white p o w e r , believed to be a carbanilide derivs,tive resulting from hydrolysis and polymerization. This observation emphasizes the importance of considering the possible effects of moisture and atrnxpheric humidity on analysis of air for imyanates. ACKNOWLEDGMENT
The author acLnowledges assistance from many persciis a t the D u Pont Jackson Laboratoi~g,the Du Pont Elastomers Laborator:?, Chestnut Run, the Du Pont Haskell Laboratory, and the D u Pont IndustIial Hygiene Laboratory. Sincere appreciation is expressed to B. W. Billmeyer, R. C. Charsha, George Limperos, A. L. Linch, A. bf. Neal, G. H. Patteu;on, R. H. Walsh, and J. A. Zapp for technical advice during this investigation. LITERAIURE CITED
Bailey, &I. E., ICirss, Voldemar, Spaunbur4i R. G., Ind. Eng. Chem. 48,P64 (1956).
Chilton, T. E.,Genereaux, R. P.,
Trans. Ana. Inst. Chem. Engrs. 25, 102 (1930). (3) Davidson, H. R., Imm, L. W., J. Opt. SOC. Amer. 39,942 (1949). (4) Davies, 0. -,., “Statistical nIeth-
ods in Rescuch and Production,” Oliver and I3oyd, London, 1947. FIAT Final Eleports 712, 722 (1946). Hardy, A. C., “Handbook of Colorimetry,” Technology Press, Cambridge, Mass., 1936. Hentschel, W.,Ber. 18, 1178 (1885). Hunter, R. S , Natl. Bur. Standards, Circ. 429, *J. Opt. SOC.Amer. 32, 509 (1942).
(9) Judd, D. B., Rnz. J. Psychol. 52, 418 (1939). -\ -
(10) Judd, D. B., Teztile Research 9, 253, 292 (1932). (11) Limperos, G., Haskell Laboratory, E. I. du Pont de Nemours & Co.,
M7ilmington, Del., private communication. (12) Mellon, ic1. G., Ferner, G. W.,J .
Phys. Chem. 35, 1025 (1931). (13) Mellon, A I . G., hlartin, F. D., Ibid., 31. 161 (1927). (14) illellbn, hi. G., hlehling, J. P., Zbid., 35,3397 (1931). (15) Mine Safety Appliances Co., Pittsburgh, Pa., Catalog 7-B, pp. 3-28. (16) Mohr, E., J. prakt. Chem. 71, No. 2, 133 (1905). (17) Naegeli, C., Tyabji, A,, Helv. Ckim. Acta 17, 931 (1934). (18) Naegeli, C., Tyabji, A,, others, Ibid. 2 1,1100 (1938). (19) Nickerson, D., Stultz, I
