September 15,1934 (5)
I N D U S T R I A L A N D E N G I N E E R I N G CH E M I ST R Y
Gorbatscheff, S. W., and Winogradowa. E. N., 2. phys. Chem.,
127, 93 (1927). ( 6 ) Gramenitski, M. J., Biochem. Z.,185, 437 (1927). (7) Remington, R. E., McClendon, J. F., and von Kolnitz, H., J. Am. Chem. Soc., 53, 1245 (1931) (8) Staiger, 2. Spiritusind., 50, 300 (1927).
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(9) Treadwell, F. P., “Analytical Chemistry,” 3rd ed., Vol. 11, p. 653,John Wiley & Sons, N. Y . , 1914. (10) Turner, R. G . , J . Am. Chem. Soc., 52, 2768 (1930). (11) Woodard, H. Q., Quimby, E. H., and Downes. H. R., Am. J . Roentgenol. Radium Therapy, 29, 308 (1933). RECEIVED January 2, 1934.
Determination of Lead Soap in Oils and Greases HARRYLEVIN,The Texas Company, Beacon, N. Y.
I
T I S FREQUEKTLY necessary during the examination of greases, car oils, extreme pressure lubricants, etc., to
determine the amount of lead soap present. Various methods have been published for this determination but most of them are inaccurate, difficult, or tedious. The methods generally involve the determination of the combined lead present, from which, by suitable factors, the percentage of lead soap is calculated. The more common methods for the determination of the combined lead are the following: 1. The direct ignition of a weighed portion of sample, the ash being recorded as lead oxide. This procedure leads to inaccurate results because the ash is practically never pure lead oxide, but contains metallic lead and usually iron oxide. 2. The direct ignition of a weighed portion of sample, followed by digestion with sulfuric acid to convert all the lead present to lead sulfate, which in turn is dissolved in ammonium acetate and subsequently precipitated and determined as the chromate. This procedure, while sound in principle, is lengthy and offers difficultips in manipulation. 3. The sample is digested with concentrated sulfuric acid followed by ignition of the mass, leaving the lead as sulfate. From this point on, the procedure is the same as the second method. This method is even more difficult than the second, the oil and sulfuric acid frothing to such an extent as to cause losses.
The procedure which has been developed in the author’s laboratory has proved universally satisfactory, even in the hands of comparatively inexperienced operators. It is based on the fact that the sample being analyzed is soluble in a homogeneous mixture of pure benzene and glacial acetic acid, and upon being refluxed the lead compounds are converted to acetate which can subsequently be precipitated as lead chromate. Incidentally, this procedure, if slightly modified, distinguishes between the organic and inorganic lead, the latter resulting either from excess of litharge used in the saponification process or consisting of lead sulfide formed b y the interaction of litharge with the sulfur compounds of the mineral oils.
PROCEDURE The reagents required are a 10 per cent potassium chromate solution, a mixture of glacial acetic acid and pure benzene (1 to 2 b y volume), and pure benzene. Two to ten grams of sample, depending upon the concentration of lead soap, are weighed into a suitable Erlenmeyer flask, 45 cc. of the glacial acetic acid-benzene mixture are added, and the mass is boiled actively under a reflux condenser for 1 hour. It is allowed to cool, and is then transferred to a globe-shaped separatory funnel, the flask being rinsed with two successive 10-cc. portions of the glacial acetic acid-benzene mixture. To the separatory funnel are added 50 cc. of distilled water, the contents are gently shaken and allowed to settle, and the aqueous layer is withdrawn into another separatory funnel. Experience has shown that when decomposition has been completed the layers separate rather sharply. Emulsions usually indicate incomplete decomposition. The benzene layer is viashed with 50-cc. portions of distilled
water until the aqueous extract is free of acetic acid. Combined aqueous washings are then filtered through wet paper to remove entrained oil, and the lead in the filtrate is precipitated as chromate by the addition of an excess of 10 per cent potassium chromate solution. When the precipitate is thoroughly settled and the upper layer is perfectly clear, it is filtered on a Gooch, washed thoroughly with hot water, dried a t 105’ C., and weighed as lead chromate. By a suitable factor the lead chromate is converted to the particular lead soap involved-for example, lead chromate multiplied by 2.381 gives lead oleate. lead chromate multiplied by 2.949 gives lead naphthenate, of a naphthenic acid whose molecular weight is 374. Tables I and I1 indicate the reproducibility of results by the different methods in the hands of a competent chemist who had not used any of these methods before. It is apparent that the proposed method was the only one which consistently gave reproducible and accurate results. The solvent used for the solution samples was a pale mineral lubricating oil. TABLE I. DETERMIKATIOK OF LEADSoap
AS
OLEATE PROPOSED
SAMPLE
METHOD1 MMETHOD 2 METHOD3 METHOD Teat 1 Test 2 Test 1 Teat 2 Teat 1 Test 2 Teat 1 Teat 2
%
%
%
%
%
%
Leadoleate,comm. 102.1 97.0 94.5 91.6 96.6 5 3 . 3 3 per cent lead oleate, solution 4.3 3.1 1.8 0.7 .,a ..a 10 per cent lead oleate, solution 11.4 1 1 . 0 8.8 5.3 ..a .a a Lost by violent spattering or uncontrollable frothing.
TABLE11. DETERbfINATION SIMPLE
OF
LEAD SOAP
AS
%
%
96.5
96.4
2.79
2.82
9.73
9.59
NAPHTHENATE
PROPOSED METHOD1 METHOD2 METHOD3 MBTHOD. Test 1 Teat 2 Teat 1 Teat 2 Teat 1 Teat 2 Test 1 Teet 2
%
%
%
%
%
%
%
%
Lead naphthenate, comm. 84.6 84.6 8 0 . 1 6S.O 86.6 8 2 . 1 86.4 86.2 3 per cent lead naphthenste. solution 2.57 2.67 2 . 2 5 1 . 9 3 1 . 3 3 1 . 2 0 2.53 2.53 10 per ’cent lead naphthenate, aolution 8.3 9 . 1 8.1 7.3 8 60 8 37 8.56 8.56
The naphthenic acid component of the lead naphthenate used in these tests had a molecular weight of 374. When it is desired to distinguish between the organically combined lead present as lead soap and the inorganic lead compounds, the procedure should be modified: The weighed sample is first refluxed with benzene, then filtered as hot as possible through the Gooch crucible, and to the filtrate is then added the required amount of glacial acetic acid to give the proportion indicated above; the rest of the procedure for organically combined lead is identical with t h a t outlined. Experience with a great many commercial lead soap lubricants has shown very few lead soaps, basic or otherwise, which are not soluble in boiling benzene. The inorganic lead compounds which remain insoluble in the benzene can be digested with nitric acid and the lead determination carried out in the usual manner. RECEIVEDFebruary 15, 1934.
