and the difference between the j ' s for diphenyl and for recrystallized tristearin is significant a t the 95y0 confidence level. Thus, one of two conclusions must be drawn: the ebullioscopic constant in toluene varies n-ith molecular weight, or the purity of the compounds decreases with increasing molecular weight and the ebullioscopic constant is a true constant. The latter conclusion u-ould fit the observed deviations in j if the compounds were contaminated with impurities of lower molecular weight. However, as the compounds used were all of high purity, it is most probable that j does vary with molecular weight, a t least in toluene. No reasons are proposed for the deviation.
more widespread usage for the determination of molecular weights of compounds of lower molecular weight. I n these applications, the amplifier on the recorder could be used, thus reducing the expense. Several approaches to increasing the usable upper molecularweight limit are being studied, such as new schemes for agitating the solution t o minimize superheating and use of thermistors of higher sensitivity.
CONCLUSIONS
(1) iishley, C. E., Reitenour, J. S.,Hammer, C. F., J . A m . Chem. Soc. 79, 5086
Although this method suffers two limitations. one of them common t o other ebullioscopic methods, that limit its usefulness for polyethylenes to X,'s of 20,000 or less, i t offers the advantage of simplicity of construction and ease of operation. Because of the speed and accuracy of the method. it should find
ACKNOWLEDGMENT
The assistance of N. Scarritt, Jr., in designing and assembling the ebulliometer is gratefully acknowledged. LITERATURE CITED
(1957).
W.R., Can. J . Chem. 37, 1508 (1959). (3) Blackmore, W.R., Can. J . Phys. 37, 1365 (1959). (4) Ibid., p. 1517. (5) Ibid., 38, 565 (1960). (6) Blackmore, W. R., Rrv. Sci. Instr. 31, 317 (1960). ( 2 ) Blackmore,
(7) Bonner, R. V., Iliinbat, M., Stross, F. H., "Sumber-Average Molecular Weights," Interscience, 4ew Tork, 1958. (8) Ezrin, If.,Claver, G. C., Abstracts, 141st Meeting, .4CS, Washington, D. C., March 1962. (9) Glover, C. -4..Hill, C. P., ANAL. CHEV.25, 1379 (1953). St,anley: R . K., Ibid., (10) Glover, C. -4., 33, 447 (1961). (11) Ibid., p. 477. (12) Lehrale, R . S.. hlajury, T. G., J . Polymer Sei. 29, 919 (1958). (13) Morawetz, H . . J . Polymer Sci. 6, 117 (1951). (14) Xeumayer, J. J., .4nul. Chim. Acta 20, 519 (1960j. (15) Nicholas, L.,.Ilokromol. Chem. 24, 173 (1957). (16) Ray, S . H., Trans. Faraday SOC.48, 809 (1952). (17) Schon, I
