January 15, 1931
INDUXTRIAL AND ENGINEERING CHEMISTRY
excellent results when the lead content of the sample is between 5 and 150 mg. Within this range the average error of the method is less than 0.2 mg. of lead. When the sample contains less than 5 mg. of lead, low results are obtained. Should the lead content of the solution be more than 150 mg., as much as 1 mg. of lead may remain in solution. 1 rcrd d r p r r t r d
-
Arid m
I
I .
P*
I
until brown fumes cease to be evolved. The sides of the beaker are washed and 0.25 cc. sulfuric acid added. The solution is boiled again for 1 to 2 minutes, diluted to 140 CC., and heated to a temperature of 90" C. It is then electrolyzed for 2 hours a t 3 amperes. The anodes are removed from the board, washed in water, alcohol, dried rapidly in an oven or on a hot plate, cooled, and weighed. The weight of lead dioxide deposited is equal to the per cent of lead when a factor weight of the sample has been used. When interfering elements are present, it is necessaryto perform a separation before electrolyzing. I n applying this method to the analysis of lead concentrates it is usually best to take a one-fourth factor weight sample. A one-half factor weight sample may be run but the error is usually greater. Care must be taken to assure a homogeneous sample. I n some instances it, is necessary to grind the sample to pass a 20Qmesh screen before satisfactory results can be obtained. This is illustrated by the data given in Table V.
Con,."+
Figure 2
Table V-Analysis
Other workers have recommended factors less than theoretical. According to this the method should give high results when the theoretical factor is used, but in these experiments high results were never obtained unless some interfering element, such as bismuth or tin, were present. The factor lead taken over lead dioxide deposited, is always 0.8662 if the proper conditions are observed. Hydrogen sulfide was used to test for the complete deposition of lead and-only traces were found after electrolysis. Table IV-Deposition of Various Amounts of PbOa Conditions of experiment: 140 cc. soln: 0.25 cc. Hasob; 2 hours; 3 PbOn TAKEN Gram
29
amperes: 90' C.: 3; cc. HNOs PbOi N O . OF FOUND DBTNS. Gram
26 6 1 1 5 1 4 2 2 22 18 5 3 5 4 5
0 0044 0.0049 0.0070 0.0100 0.02501 0.11555 0.1727 0.2295 0.2870 0.3451 0.4024
A v ER A G E DEVIATION Gram
.....
%
of Lead Concentrates SAMPLE SAMPLE 150-MESH 2OO-MESH
% 53.88 53.68 53.60 53.70 53.88 54.08
5
Run
by-A. W.
% 53 .92 53.92 54 04 53. 88O 53.84' 53.84' Av. 53.91 ;h 0.05
Holmes, Bureau of Mines.
Literature Cited (1) Guess, Bull. Am. Insl. Mining Eng., 1239 (1905). (2) Holmes and Morgan, IND. ENQ. CHEM.,Anal. Ed., 1, 210 (1929).
.....
0.0013 0.0008 0.0007 0 0004 0.0001 0.0001 0.0001 0.0000 0.00001 0.00005 0,0005 0.0014 0.0012
Determination of Hydrogen Sulfide in Refinery Still Gases' A. R. Scharnagel and A. W. Trusty LOUISIANA OIL REFINING CORPORATION, SHREVEPORT, LA.
0.0013
0.0017
Procedure
The procedure as finally adopted and recommended for use when there is no interference from other elements is as fol-
PbO, cont.nt d f
ORIGINALSAMPLE ~OO-MESH
so/".,;b"
Figure 3
lows: A sample, the amount depending upon the per cent of lead, is weighed into an ordinary 150 cc. electrolytic beaker, 30 to 35 cc. of nitric acid are added, and the sample is boiled
HE iodine titration method has always been a standard method for the determination of hydrogen sulfide, but with refinery still gases this method is inaccurate because of the reaction of the gaseous unsaturated hydrocarbons with the iodine. The following method has been used in our laboratory: 100 cc. of 0.1 N acid lead nitrate is placed in a Fisher gas washing bottle or any convenient scrubber. The gas to be tested is passed through the bottle and metered with a gas meter, or a known volume of water is displaced. A second wash bottle with 100 cc. of 0.1 N lead nitrate is placed directly after the first wash bottle. With the slightest discoloration of the second bottle, the rate of flow of the gas is reduced to insure all of the hydrogen sulfide being caught in the first bottle. The second bottle is useful also when testing a gas in which the quantity of hydrogen sulfide is unknown, as the second bottle will be an indicator when the first bottle becomes spent. The first bottle is Gltered, made up to volume, and aliquot portions titrated with ammonium molybdate solution. With convenient factors on the solutions, the method is rapid and accurate. 1
Received N6vembec 3, 1930.
