INDUSTRIAL AND ENGINEERING CHEMISTRY
200
anomalous wave is due to a discharge of water under the specified conditions: H20
+ e +H + OH-
The water current a t a potential of -1.35 to -1.4 volts is proportional to the total current flowing. Suppose, for example, that under certain conditions the thallium wave is equal to 5 microamperes and the water wave to 4. When the thallium concentration is doubled, the water wave becomes equal to 8. In addition to being dependent upon the total current, the concentration and kind of indifferent electrolyte present, the water wave depends greatly upon the characteristics of the capillary. The n-ater current decreases markedly with increasing drop time. From the analytical viewpoint the “water wave” can be the cause of serious errors in the interpretation of current-voltage curves, especially in the determination of constituents, the waves of which yield diffusion currents a t potentials more negative than about 1 volt. Under such conditions only one wave is found, since the water wave overlaps with the wave of the reduced constituent. Consequently, the diffusion current measured is not equal to that of the reduced constituent, but is equal to the sum of the latter and the water wave. For example, in the electroreduction of zinc, iodate, or bromate a marked increase in the “apparent” diffusion current is found with increasing concentration of potassium chloride, if the concentration of the chloride is made greater than 0.5 N . Actually, the true diffusion current of the above species is hardly affected by the concentration of potassium chloride in solution. For example, in the electrolysis of a 5 X lo-‘ M potassium iodate solution in 1 A‘ potassium chloride using a capillary with a drop time of 3.60 seconds, Orlemann and Kolthoff (11) found an “apparent” diffusion current of 14.20 microamperes a t - 1.45 volts, whereas the true diffusion current was only 11.30. When the drop time was increased, the relative difference between the apparent and the true diffusion currents became much greater.
Vol. 14, No. 3
I n quantitative polarographic work solutions which contain a high concentration (1to 2 N ) of indifferent electrolyte(e. g., in steel analysis)-are often electrolyzed. When only one reducible constituent is present it is not essential to eliminate the water wave because a calibration line with known concentrations of the constituent can be obtained in the particular medium. However, when the solution contains a mixture of reducible substances, it is not easy to eliminate the effect of the water current upon the results by a set of calibrations, because the water current is proportional to the total current. In the polarographic analysis of a mixture in a medium of high salt concentration it becomes essential to eliminate the water wave entirely. This can be done by the addition of 0.01 per cent of gelatin to the solution. Other capillary-active substances, which are often used as maximum suppressors, also affect the water wave; they do not eliminate it completely as gelatin does, but shift the wave to more negative potentials. Sext to gelatin the most effective of the capillary active substances investigated is tylose, which shifts thc wave to a potential of - 1.6 volts. In order to avoid any complications by the water wave in work with the dropping electrode, the author recommends that 0.01 per cent of gelatin be added to solutions, the salt concentration of which is larger than 0.5 N .
Literature Cited (1) Ilkovic, D., Collection Czechoslov. Chem. Commun., 6, 498 (1934). (2) Kolthoff, I. M., and Barnum, C., J . Am. Chem. SOC.,62, 3061 (1940). (3) Kolthoff, I. M.,and Lingane, J. J., “Polarography, Polarographic Analysis a n d Voltammetry, Amperometric Titrations”, New York, Interscience Publishers, 1941. (4) Kolthoff, I, M., a n d Miller, C. S., J . Am. Chem. SOC.,62, 2171 (1940). (5) Ibid., 63, 1013 (1941). (6) Ibid., 63, 1405 (1941). (7) Kolthoff, I. M.,and Orlemann, E. F., Ibid., 63, 2085 (1941). (8) Lingane, J. J., thesis, University of Minnesota, 1938. (9) Miller, C . S., thesis, University of Minnesota, 1940. (10) Orlemann, E. F., thesis, University of Minnesota, 1941. (11) Orlemann, E. F., and Kolthoff, I. M.. J . Am. Chem. SOC.. 64 (March, 1942).
Determination of Mixed Aniline Points
of Hydrocarbon Solvents B. H. SHOEMAKER
D
AND
J. A. BOLT, Standard Oil Company (Indiana), Whiting, Ind.
URIKG the past few years, considerable attention has been given to methods of determining the solvency characteristics of paint, varnish, and lacquer thinners. While the viscosity method represents an ultimate means of determining the relative value of various thinners, a more simple test, such as apiline point, probably will continue to be used for controlling the uniformity of a given thinner. With the development of petroleum naphthas of substantial aromatic content, it has been necessary to use the mixed aniline point test. The mixed aniline point has been defined as the minimum miscibility temperature in degrees centigrade of a mixture of 10 cc. of anhydrous aniline, 5 cc. of the thinner under test and 5 cc. “of any naphtha whose aniline point is 60” C.” ( 3 ) . McArdle (1, 4) states that the nonaromatic diluent shall be “a mineral spirit (regardless of boiling point) ” having a 60” C. aniline point. Experiments described herein indicate the necessity for defining the diluent more closely. The mixed aniline points, as defined above, have been determined on a number of experimental high-solvency naphthas
of varying aromatic content. Two sets of tests were made, one using A. S. T. M. precipitation naphtha as the diluent and the other using mineral spirits. The inspection tests of the two diluent naphthas are shown in Table I. Figure 1 shows the relationship obtained between the two sets of tests after classifying the high-solvency naphthas under
TABLE I. IXSPECTION TESTS A. s. T. iy. Gravity, ‘A. P. I. A. S. T. M. distillation D-86 Initial b. p., F. 10% recovery, O F. 5 0 7 ~recovery, O F. 90% recovery, O F. End point, O F. Aniline point, C.
Precipitation Naphtha
Mineral Spirits
71.9
48.9
140 150
234
305 323 345 388 423
59.6
59.7
164
195
March 15, 1942
ANALYTICAL EDITION
201
consideration into three boiling point ranges-200" to 275", 275" to 350°, and 350" to 415" F., respectively. It will be noted that the mixed aniline points determined with A. S. T. hf. precipitation naphtha are appreciably lower than when the mineral spirits are employed. These differences are not constant, but vary with the concentration of aromatics and with the boiling range of the solvent naphthas as shown by the following data taken from the curves: Nixed aniline point with mineral spirits 100 c. 150 c. 200 c. Mixed aniline aoint (' C.) with precip. naph. ' For 200-276 F. naphthas 9.5 15.5 For 275360O F. naphthas 3' 8.7 14,s For 350-415'F. naphthas . 9 14.4
.
Mixed aniline ooint with mineral &its Mixed,aniline point ( " C.) with precig. naph. For200475 F. naphthas For 275-350' F. naphthas For 350-415' F. naphthas
26'C.
30" C.
21.4
20.3 20
27.3 25.7
This same effect of the variation of the paraffinic diluent on the mixed aniline point is observed with c. P. toluene. Baker's c. P. toluene, having an na$ of 1.4951 shows the following mixed aniline points:
c. Using A. S. T. M ,precipitation naphtha
IJsing mineral spirits
-0.9 +7 6
From the above discussion it is evident that the paraffinic diluent used for determining mixed aniline points should be defined more rigidly than it has been in the past. It is recommended that this diluent be identified by its aniline point and by its mixed aniline point with c. P. toluene. Some users employ a diluent equivalent to mineral spirits which has a mixed aniline point with c. P. toluene of about 7.5" C. McArdle (2) proposes that this diluent have an aniline point of 60" C. and a mixed aniline point of 10 * 0.5" C. with c. P. toluene. It is suggested by the authors that the manufacturers and consumers of high-solvency naphthas cooperate to define the specifications for the diluent used to determine mixed aniline points.
Literature Cited (1) McArdle, E. H., Chem. & Met. Eng., 44, 601 (1937). (2) McArdle, E. H., private communication. (3) Paint,O i l & Chem. Rev.,p. 19 (Nov. 24, 1938). (4) Sweeney, W. J., and McArdle, E. H., IND. ENG.CHEM.,33, 787 (1941).
FIGURE 1. EFFECTOF DILUENTON MIXEDANILINE POINTSOF HIGH-
SOLVENCY NAPHTHAS
PRESENTED before the Division of Petroleum Chemistry a t the 102nd Meeting of the AMERICAN CHEMICAL SOCIETY,Atlantic City, N. J.
