MAY 15, 1935
ANALYTICAL EDITION
TABLI~ I. SEPARATION OF SMALL AMOUNTSOF LEAD FROM COPPER Nature of Bolution
Insoluble Lead Salt PbSOi PbCrOc PbCrOc PbCrOa PbCrOc PbCrO4 PbCrO4 PbCr04 PbCOa Pbs(PO4)r
Collector MnOl MnOn MnOt Fe(OHh Norite Fe(0H)a MnO(0H)z Norite CaCOs CadPOch CaCOs
Result Unsatisfactory Unsatisfactory Unsatisfactory Unsatisfactory Unsatisfactory Unsatjsfactory Unsatisfactory Unsatiafaotory Unsatisfactory
+ Satisfactory
TABLE11. SEPARATION OF LEADIN COPPER Fhmple
% Lead
Sample
% Lead
10. This method was used in all subsequent work, and will therefore be described in detail. A 50-gram sample of copper was washed with hot concentrated hydrochloric acid, followed by distilled water, and dissolved in 200 CC. of concentrated nitric acid. The brown fumes were boiled off, and 1200 cc. of water and 380 cc. of concentrated ammonium hydroxide were added. Then 2 cc. of disodium phos hate and 50 cc. of ammonium carbonate solutions were added: the solution was mixed well, and 25 cc. of calcium chloride solution added all at once with stirring. After standing overnight it was filtered through a No. 4 dena glass crucible. The preci itate was dissolved in 25 cc. of hydrochloric acid, neutralized witE ammonium hydroxide then acidified with a few drops of acid and saturated with hydrogen sulfide before filtering. The sulfides were dissolved in nitric acid and concentrated to 5 cc. All the lead is separated by this method. A
183
second precipitation showed no trace. Two milligrams of lead were added to this lead-free copper solution and a third precipitation was made. This contained the 2 mg. A fourth precipitate again showed no lead.
A number of samples of refined copper from various sources were subjected to this method. The results obtained by comparison of their spectrograms with those of standards taken on the same plate, according to the method of Nitchie (4),are given in Table 11.
Preparation of Standards SOLUTION A. Three grams of lead-free copper were dissolved in 300 cc. of nitric acid. SOLUTION B. One gram of test lead was dissolved in a little nitric acid and diluted t o one liter. Four cubic centimeters of B and 6 cc. of A were mixed. Then 5 cc. of the mixture were mixed with 5 cc. of A to give the second standard, and 5 cc. of the second standard were mixed with 5 cc. of A to give the third standard. In this way nine standards were prepared with the following concentrations: 2, 1,0.5,0.25,0.125, 0.0625,0.0312, 0.0156, and 0.0078mg. per 5 cc. When 0.1 cc. of each of the standards was dried on a graphite electrode and arced, the lead line a t 2833 A. graded nicely in intensity and was visible in the first seven. The smallest amount of lead detectable by this method and by the particular Gartner Littrow-type spectrograph used in this work was therefore 6 X lo-’ gram.
Literature Cited (1) Heath, “Analysis of Copper,” p. 221, New York, McGraw-Hill Book Co., 1916. (2) Jones, Analyst, 58, 11 (1933). (3) Keffer, “Methods in Non-Ferrous Metallurgical Analysis,” p. 118, New York, MoGraw-Hill Book Co., 1928. (4) Nitchie, IND. ENG.CHEW,Anal. Ed., 1, 1 (1929).
RECFOIVBD February 8, 1935.
Detection and Volumetric Estimation of Alkali Metals ROBERT S. BARNETT, The Texas Company, Beacon, N. Y.
I
T IS SOMETIMES not easy to decide by means of common reagents whether or not the alkalinity of an ash is due to alkali metal. For example, an ash from a mixed
sometimes encountered when alkaline earth compounds alone are Present. It should not be confused with the soapy frothy filtrate, yielding a precipitate with barium chloride, due to alkali soaps.
base grease containing calcium and sodium Presents Somewhat the same flaky appearance as an ash from a calcium soap grease. The usual flame test is uncertain in this case.
This test has the advantage of preferentially detecting alkalinity due to sodium or potassium, not showing sodium or potassium that may be also presentin neutral combination as chlorides or sulfates. Other sodium or potassium reagents give information only as to the total content of these metals. This test is particularly adapted to distinguish sodium and potassium from calcium in the ash of lubricating greases.
Soap Formation as a Test The qualitative test here outlined makes use of the insolubil,ity of alkaline-earth oleates and the solubility of alkali oleate in water.
A portion of the hot, aqueous, filtered extract of the alkaline ash is added with shaking to a hot alcoholic solution of oleic acid until the mixture is alkaline to phenolphthalein. The alcoholic strength must be kept above 50 per cent at all times t o prevent hydrolysis of the soap formed. The solution is evaporated on the steam bath with a current of air blowing into the flask until the odor of alcohol is very faint. Five volumes of distilled water are d d e d to the aqueous residue, the solution is warmed and shaken, and any alkaline-earth soa s are filtered off. The filtrate it3 examined for ability to fro& on shaking and tested for alkali soap by the addition of bariuri chloride solution. A white, curdy precipitate confirms alkalinity due to alkali metal in the ,ash. A faintly opalescent filtrate that does not froth nor increase in cloudiness upon the addition of barium chloride, is
Quantitative Volumetric Determination The quantitative estimation was designed primarily as a fairly rapid method for alkali metals in the ash obtained by the ignition of petroleum products and compounds. It has been extended to the determination of these metals in their sulfates, to which form many other of their salts can be easily converted. It is applied in the cases cited by treating the ash or salt with concentrated sulfuric acid, and decomposing the excess sulfuric acid and heavy metal sulfates by heating carefully until no more sulfur trioxide fumes are given off.
INDUSTRIAL AND ENGINEERING CHEMISTRY
184
If they ale both present, this titration would represent the total alkalinity due to alkali metals.
ON KNOWNMIXTURES TABLEI. RESULTS
Weight of Sample Grams
Mixture Ammonium sulfate, calcium hydroxide and sodium oarboAate Fused sodium chloride Potassium nitrate
Sodium Carbonate In mixture Found
Sodium In mixture Found
%
%
%
0.176 0.240 0.366 0.146
35.2 37.1
35.2 37.2
'.
... .
15.3 16.1 39.4
0.406 0.230
,. ..
.. ..
%
15.3 16.2 39.1 40.0 Potassium 38.6 38.6 38.6
.. ..
The sulfated residue is dissolved as far as possible in water. Solid barium hydroxide is added in excess to precipitate sulfates as barium sulfate, and to convert sodium and/or potassium sulfate to the hydroxide. Na2S04 Ba(OH)* +2NaOH Bas04 J. The precipitate, which may include other undissolved alkalineearth sulfates, is filtered off and washed well with hot water, and ammonium carbonate is added to the boiling combined filtrate and washings to precipitate soluble alkaline-earth compounds as carbonates. The carbonates are filtered off, washed well with hot water, and the filtrate is boiled down to one-fifth of its volume to decompose and get rid of excess ammonium carbonate. (There should be no odor of ammonia at this point.) After cooling, any slight recipitate of alkaline-earth carbonates is filtered off, washed witl water at room temperature, and the combined filtrate and washings are titrated to a methyl orange end point with 0.1 N acid in the usual manner. The acid consumed is calculated to per cent sodium or potassium, as the case may be.
+
+
VOL. 7, NO. 3
Since the estimation is based on getting the alkali metals in the form of soluble compounds, it is not necessary to burn off all carbon or ignite the ash to constant weight. This reduces the loss by volatility of alkali metal compounds, which is a troublesome factor in the usual gravimetric determinations of the alkali metals. It is hoped that this method may be useful in estimating alkali metals in other fields of analytical procedure.
Results on Unknown Mixtures Neutrally bound alkali metals in the ash may be calculated from the difference between the result obtained by the method as outlined and the result obtained by determining the alkalinity of the ash to methyl orange. Results of tests on ash from soda-base grease, containing 0.93 per cent of total sulfur, showed the following. Alkalinity of ash as.sodium, uncorrected Total sodium by this method, per cent Neutrally hound aodium, per cent
30.8 34.6 3.8
30.9 34.8 3.8
Acknowledgment The author wishes to thank Harry Levin and Karl Uhrig for helpful criticisms and suggestions. RECEIVED February 4, 1935.
Detection of Benzene in Alcohol A. C. LANSING, Commercial Solvents Corporation, Terre Haute, Ind.
B
ENZENE may occur in alcohol in small amounts, and is undesirable in alcohol used for some purposes. The presence of benzene may be due to faulty process, or to accidental contamination. When the benzene content is too small for any of the turbidity tests with water, indications of its presence are usually obtained through taste and odor. Unfortunately, taste and odor tests do not give uniformly positive selective indications of the presence of benzene in low concentration. A direct and sensitive chemical test for small amounts of benzene in alcohol is therefore of value in the examination of alcohol. A reliable method was desired for detecting benzene in concentrations of the order of 1 part by volume in 10,000, in alcohol of good quality otherwise. After unsatisfactory results by other methods a procedure involving concentration of the benzene by extraction, nitration of the extract, and color reaction of the nitration product was devised and applied with satisfactory results.
Reagents Required Carbon tetrachloride, reagent grade. Acetone, reagent grade. Amyl alcohol (redistilled crude fusel oil) refluxed with strong caustic soda solution, and distilled from the alkali, collecting for use the dry fraction boiling at 128" to 132' C. Nitrating acid: 70 grams of reagent 20 per cent oleum, 45 grams of reagent sulfuric acid of specific gravity 1.84, and 43 grams of reagent nitric acid of specific gravity 1.42. Sodium sulfate solution, containing 10 grams of the anhydrous salt in 100 cc. of solution. Caustic soda solution, 140 grams of reagent (sticks) made up to 250 cc. at room temperature.
Procedure If the alcohol contains much above 0.01 per cent benzene by volume, as indicated by test on the undiluted sample, it is diluted
to approximately that value with alcohol free from benzene, A 40-cc. portion is placed in a 100-cc. glass-stoppered cylinder with 6 cc. of carbon tetrachloride. Distilled water is added to the 90 cc. mark, followed by 10 cc. of sodium sulfate solution. The cylinder is stoppered, shaken thoroughly, and allowed to stand until the layers separate sharply. Five cubic centimeters of the bottom layer are transferred by pipet to a test tube. Three cubic centimeters of nitrating acid are measured in a small cylinder and added to the test tube, which is shaken carefully but thoroughly. During 10 minutes the tube is shaken twice more, and at the end of that time, 20 cc. of distilled water are added, preferably rapidly from a cylinder. After mixing by pouring into another test tube and back again, the bulk of the water layer is decanted and discarded. The lower layer with a small amount of water layer is placed in an evaporating dish on an electric hot plate. When the carbon tetrachloride is gone, the dish is emptied into the same test tube just used and is rinsed into this tube with 1 cc. of amyl alcohol. The dish is then rinsed into the tube using 4 cc. of caustic soda solution. The tube is mixed by swirling and then 1 cc. of acetone is added, the tube is swirled again, and placed in a rack for observation of color produced in the top layer.
Indications Pure benzene a t the concentralion 1 in 10,000 by volume in a rectified alcohol of ordinary purity gives by this test a red color with a purple quality in the top layer. This color holds for some hours, and finally fades to a dull orange-red. As the benzene content rises above 0.01 per cent, the color produced soon becomes too dark for identification, and dilution with alcohol free from benzene is necessary. Pure toluene gives a slightly brownish yellow and reagent xylene (chiefly m-xylene) produces a definite though not intense green, which fades in 30 minutes, giving way to a dull orange. Blank runs should always be run in duplicate with a test series; they give a light clear lemon yellow. Thorough cleaning of the apparatus between tests is necessary t o maintain blank indications. Among other hydrocarbons tested, denaturing gasolines gave yellow colors of somewhat orange cast and a cer-
