JULY 15, 1937
339
ANALYTICAL EDITION
large volumes of air drawn through this connection when the suction is on, which keep the upper end of the flask and the bulb-stopper cool, any action on the rubber is very greatly minimized. Furthermore, the operator can manipulate his flasks with perfect comfort and safety. If a larger number of units is desired, it is only necessary to increase the size of the water supply and drainage pipes. For the six-unit set a 3.75-cm. (1.5-inch) supply and a 7.5-cm. (3-inch) drainage pipe serve adequately when the pressure is 2.8 kg. per sq. om. (40 pounds) or more. For a 12-unit set a 6.25-em. (2.5-inch) supply and a 10-em. (4-inch) drain pipe would suffice.
The material for the apparatus, including pressure gage and shutoff valve, costs only $25. The set has been in constant use for more than 2 years, during which time hundreds of digestions have been made without any breakage or replacement of a single connection.
Acknowledgment The writer wishes to express his thanks to Edward Ehmke for the construction of the diagram. RECEIVED March 4, 1937.
Diphenylguanidine as a Standard in Neutralization Processes WILLIAM M. THORNTON, JR., Loyola College, AND CHARLES L. CHRIST, Johns Hopkins University, Baltimore, Md.
So“’:
4 14 years ago Carlton ( 7 ) proposed the use of symmetrical diphenylguanidine as a reference substance in acidimetry and alkalimetry. His test determinations are excellent; hence, in view of the obvious advantages to be gained through the employment of a soluble and sufficiently strong (18) organic base, it is rather surprising that the method has not attracted more widespread attention. Several other authorities (6, 9, 14, 16), presumably on the basis of experience, have commented upon the material in question with great lack of agreement. Accordingly, the somewhat controversial state in which the subject seems to exist led to the present re-examination.
per cent of the lower value, leads to the conclusion that diphenylguanidine, as procured in the open market, may not yield a reliable product under Carlton’s treatment (7). On the other hand, could it be readily purified, such an organic base would be an eminently convenient volumetric standard. In fact, diphenylguanidine itself seems to react definitely with a strong acid, and the end point is sharp and easily discerned. The present authors are planning to pursue the investigation further in the hope of either preparing really pure diphenylguanidine in a way that will not be too difficult or, acting upon the suggestion of Callan and Strafford (6), obtaining triphenylguanidine of the correct composition.
Experimental
Literature Cited
In putting the matter to the test, reliance was placed upon constant-boiling hydrochloric acid; for the composition of‘ aqueous hydrogen chloride, when distilling a t a fixed temperature under the existing pressure, appears to have been exhaustively studied (1-5, 8, 10, 11, I S , 16, 1’7, 19, 21-27). Having prepared a considerable quantity of such acid, an approximately 0.1 N solution was obtained by diluting an appropriate amount of it to the requisite volume. The normality factor of the resulting liquid was calculated and found to be either 0.10057 ( I S ) or 0.10059 (10). For greater surety, the value of the solution was established gravimetrically by precipitating the chloride ion with silver nitrate, taking the usual precautions that make for accuracy (12, 20). Two such experiments showed the hydrochloric acid to be 0.10064 N and 0.10049 N . In the purification of diphenylguanidine the instructions of Carlton (7) were conscientiously followed, using a supposedly high-grade specimen of the base, which had been purchased from a reputable supply house. Moreover, in carrying out titrations with the above-described hydrochloric acid, Carlton’s “double indicator” (bromophenol blue and methyl red) was introduced into the alcoholic solution of the recrystallized diphenylguanidine to reveal the point of complete reaction. Four experiments yielded the following concordant results: 0.10114 N , 0.10117 N , 0.10114 .V, and 0.10111 N , the average of which is 0.10114 N .
(1) Bonner, W. D., and Branting, B. F., S. Am. Chem. Soc., 48. 3093 (1926). Bonner, W. D., and Titus, A. C., Ibid., 52, 633 (1930). Bonner, W. D., and Wallace, R. E., Ibid., 52, 1747 (1930). Briggs, T. R., J. Phys. Chem., 28, 644 (1924). Cadbury, W. E., Jr., S. Chem. Education, 12, 292 (1935). Callan, T., and Strafford, N., S.SOC.Chem. Ind., 43, 1T (1924). Carlton, C. A,, J . Am. Chem. SOC.,44, 1469 (1922). Carriirre, E., and Amaud, Compt. rend., 179, 1265 (1924). Chakmakjian, H. H., S. Chem. Education, 8, 2060 (1931). Foulk, C. W., and Hollingsworth, M., J. Am. Chem. SOC.,45, 1220 (1923). Hendrixson, W. S., Ibzd., 37, 2352 (1915); 42, 725 (1920). Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorganic Analysis,” p. 587, New York, John W-iley & Sons, 1929. Hulett, G. A,, and Bonner, W. D., J . Am. Chem. Soc., 31, 390 (1909). Kling, A., and Lassieur, A., Chimae & industrie, Special No.. 110 (May, 1924). Kolthoff, I. M.. and M e n d H., ”Volumetric Analysis.” tr. by Furman, Vol. 11, p. 101, New York, John Wile; & Sons, 1929. MacInnes, D. A., and Cowperthwaite, I. A., J . Am. Chem. SOC.,53, 558 (1931). MacInnes, D. A., and Dole, M., Ibid., 51, 1125 (1929). Metz, L., 2. Elektrochem., 34, 292 (1928). Morey, G. W., J . Am. Chem. SOC.,34, 1029 (1912). Richards, T. W., and Willard, H. H., Ibid., 32, 28 (1910). Roscoe, H. E., Ann., 116, 213 (1860). Roscoe, H. E., and Dittmar, W., Ibid., 112, 343 (1859); J . Chem. Soc., 12, 128 (1860). Shaw, J. A., IND.E m . CHEM.,18, 1065 (1926). Sheldon, J. L., J . Chem. Education, 12, 377 (1935). Smith, G. F., and Croad, G. F., IND.ENG.CHEM.,Anal. Ed., 9, 141 (1937). Vrevskii, M. S., 2. physilc. Chem., 112, 109 (1924). Vrevskii, M. S.,Zavarickii, N. N., and Sharlov, L. E., J . Russ. Phys.-Chem. Soc., 54, 360 (1923).
Conclusions This discrepancy between the normality deduced from constant-boiling hydrochloric acid (0.10058 N ) and obtained by titrating the basic substance, amounting to nearly 0.56
RECEIVED March 1, 1937.
