ANALYTICAL EDITION
JANUARY 15, 1936
19
physical properties of the purified sample with those given by Ellis and Reid (3) for a pure sample of n-butyl mercaptan which analyzed 100.3 per cent by the iodometric method, suggests that the authors' redistilled sample was still impure. Since the analysis for total sulfur by the Carius method indicated a purity of 99.8 per cent, the sample appears to have been contaminated by an inert sulfur compound. PURIFIED TABLEV. ANALYSISOF n-BukL MERCAPTAN BY FRACTIONATION Weight of Sample
Concentration of Kerosene Solution
Uram
Gram/100
0.05504
0.1183
0.04732
0.1271
0,05084
%
Oram
CC.
0.1376
Purity of Sample
Found 0.1344 0.1339 0.1339 0.1157 0.1152 0.1240
97.7 97.3 97 .a 97.8 97.7 97.6 Av. 97.57
TABLEVI. PROPERTIES OF SAMPLE
Boiling point,
O
n-Butyl Mercaptan Sample purified by fractionation 98.0-98.3 (760 mm. Hg) 1,4392
Ellis and Reid 98.6-99.0 (768 mm. Hg) 1.4401
C.
ng
Purity, % Iodometric method Potentiometric method
100.3
97.1 97.6
PRECISION. The relative accuracy of individual determinations is governed by two factors-the solubility of the sample in alcohol and the amount of silver nitrate consumed per sample. The end point of titrations can be established with an accuracy of k0.02 cc. This amount indicates 2 X 10-7 mole of mercaptan in the sample, which should be the error in the absolute amount of mercaptan found in the titration. Consequently, the precision shown in Table VI1 can be expected, if 10 cc. of sample are added to the cell. TABLEVII. PRECISION
a
Molality of Sample
Mercaptan in Sample"
Calculated Error
%
%
0.1 0.01 0.001 Molecular weight = 100.
1.0 0.1 0.01
*0.02 hO.2
s . 0
The experimental results of Tables IV to VI agree reasonably well within the calculated limits, considering that the extreme precision indicated by the calculations for the titra-
CC. O f
0.01 N AgNO3
FIGURE 5. TITR.4TION O F MERCAPTANS I N A SAMPLE OF CRACKED GASOLINE FROM CALIFORNIA PETROLEUM tion of more concentrated solutions could be verified only by observing special precautions. The somewhat erratic results obtained with ethyl mercaptan were probably due to its volatility. Table VI11 shows the reproducibility of mercaptan determinations in a sample of cracked gasoline from California crude; Figure 5 shows the reproducibility of the titration curves. Since solution was approximately 0.0025 M with respect to mercaptan, the expected error was *0.2 X 4 = *0.8 per cent. The maximum discrepancy found experimentally was about 2.0 per cent, an error of * L O per cent, which is in reasonable agreement with the calculated value. TABLEVIII. DETERMINATION OF MERCAPTANS IN CRACKED GASOLINE FROM CALIFORNIA CRUDE Size of Sample
CC. 10.0 10.0 10.0 10.0
0.01N AgNOs Required
cc.
2.70 2.70 2.70
2.66
Mercaptan Mol e / l . 0.00270 0.00270 0.00270
0.00265
Mercaptan Sulfur
% 0.0115 0.0115 0.0116 0.0113
Literature Cited (1) Bond, G. R., Jr., IND. ENQ.CHEM.,Anal. Ed., 5, 257 (1933). (2) Borgstrom, P., and Reid, E. E.,Ibid., 1, 186 (1929). (3) Ellis, L. M., Jr., and Reid, E. E., J. Am. Chem. Soc., 54, 1674 (1932). (4) Kimball, J. W., Kramer, R. L., and Reid, E. E., Ibid., 43, 1199 (1921). (5) Kolthoff, I. M., and Furman, N. H., "Potentiometric Titratione," pp. 70 et seq., New York, John Wiley & Sons, 1926. (6) Malisoff, W. M., and Anding, C. E., Jr., IND.ENG. CHIM., Anal. Ed., 7, 86 (1935). (7) Malisoff, W. M., and Marks, E. M., IND. ENQ.C H ~ M23, . , 1114 (1931). (8) Yule, J. A. C., and Wilson, C. P., Jr., Ibid., 23,1254 (1931), RBCE~IVED November 6, 1935. Presented before the Division of Petroleum Chemistry at the 90th Meeting of the American Chemical Society, Ban Francisco, Calif., August 19 to 23,1935.
IRON GALLATE INKS-LIQUIDAND POWDER. A general study
of iron gallate writing ink was undertaken a t the National Bureau of Standards in an attempt to improve the keeping quality of ink without increasing the acid content. All inks of this type contain iron, and since the standard ink contains 3 grams of iron per liter, this figure was used as the starting point in devis-
Reaction Time-Hours
FIGURE 4. OXIDATION OF 0.01 M~-BTJTYLMERCAPTAN BY PEROXIDES IN VARIOUS SOLVENTS
ing the ink formulas. Experimental inks, using different materials in varying concentrations, were prepared and tested according t o the Federal Specification. The use of gallic acid without tannic acid produced an ink with greater stability, and consequently the acid content could be decreased. This, in turn, decreased the corrosion of steel pens. The resulting ink had remarkably good stability. This modified formula could be adapted to the preparation of an ink powder without changing the characteristics of the ink.
