January, 1945
ANALYTICAL EDITION
containing 70 mg. of titanic oxide. By comparing determinations 17 and 18 with 21 and 22 it is seen that the precipitation of titanic phosphate does not eliminate the titanium error, altnough the error with 70 mg. of titanic oxide in the presence of excess phosphate is no greater than with only 35 mg. of titanium in the absence of phosphate. It is evident that the simplified procedure is applicable to the analysis of a variety of calcareous materials, including limestones, Portland-type cements, phosphate rocks, and similar products, and it is capable of yielding results that rival in accuracy those obtained by the laborious classical procedures.
41
By employing a double precipitation of the calcium oxalate i t may also be possible to apply the method with advantage in the analysis of calcium-titanium pigments. LITERATURE CITED (1) Fowler, R. H., and Bright, H. A., J . Reaemch Nat. Bur. Standards
15, 493 (1936). (2) Kolthoff, I. M.. and Sandell, E. B., “Textbook of Quantitative Inorganic Analysis”, New York, MacmiUan Co., 1943. Jr., and Rieman, W., 111, IND.ENO.CHEM., (3) McComas, W.H., ANAL.ED., 14, 929 (1942). (4) Richards, T. W., McCdrey, C. F., and Biabee, H., Proc. Am. A d . Arts Sei., 36, 377 (1901).
Analysis of Manganese Bronze HAROLD RAVNER, Naval Research Laboratory, A method is proposed whereby, with the use of a single sample weight, copper, lead, tln, iron, and nickel may be accurately determined in mangenew bronze. Copper and lead are plated out in the presence of hydrofluoric acid which serves to hold tin in solution. Tin is subsequently separated from iron and nickel with hydrogen sulfide, reduced with lead, and titrated with potassium iodide-iodate solution. The hydrogen sulfide separation also serves to reduce iron to the ferrous condition, in which state it is determined b y tibation with ceric sulfate solution. Nickel i s precipitated from the resultant solution with dimethylglyoxirne. Results of the anelyris of several Bureau of Standards samples of mangenese bronze check closely with those obtained b y longer conventional methods.
T
H E accurate analysis of a bronze containing lead, m a n g e nese, iron, and nickel in addition to copper, tin, and zinc is, in general, a time-consuming process. Several procedures may be used for the analysis of all the elements present, but conventional methods now in use demand such devices as double precipitations, recovery from filtrates, and the use of separate samples for different elements in order to obtain satisfactory results. Thus, Lundell and Scherrer (3)point out that in the initial attack of the alloy with nitric acid, tin is incompletely precipitated in the presence of more than 0.25% of iron, and other elements, particularly iron, contaminate the precipitate in varying degrees. It is thus evident that recoveries are necessary a t the very outset of the analysis. The purpose of this paper is to show how, by an adaptation of procedures which have already been worked out (4, 5, 6),these difficulties may be avoided and an accurate analysis of a bronze obtained. McCay (5) has shown that in nitro-hydrofluoric acid, copper and lead may be quantitatively separated from stannic tin by electrolysis, no hydrolysis of the latter taking place in the presence of hydrofluoric acid. This fact is the basis of the proposed procedure. Solution of the alloy is effected in nitro-hydrofluoric acid. After electrolytic deposition of lead, sulfuric acid is added and electrolysis is continued until copper is completely deposited. Hydrofluoric acid is then removed by evaporation of the solution in a platinum dish to fumes of sulfuric acid. The solution is diluted and tin is separated from the remaining elements by precipitation with hydrogen sulfide. Tin is then determined by reduction with lead and titration with potassium iodide-iodate solution. The tin sulfide filtrate is boiled to expel hydrogen sulfide; and iron, now in the ferrous condition, is determined by titration with ceric sulfate. After titration of iron, nickel is precipitated with dimethylglyoxime from a slightly ammoniacal solution containing citric acid. Manganese and aluminum are determined on separate samples with slight variation of accepted procedures. For the sake of completeness, these procedures are included in this paper.
Anacostia,
D. C. PROCEDURE
DETERMINATION OF COPPEB AND LEAD. Transfer 2.0000 grams of sample to a 400-ml. Vycor beaker (iron-free). Add in order 15 ml. of water, 0.75 to 1.0 ml. of hydrofluoric acid (480/0), and 10 ml. of nitric acid (sp. gr. 1.42), and cover with a platinum lid. Allow to stand until solution is complete and then boil to expel oxides of nitrogen. Rinse down the lid and beaker with a jet of water and dilute to 200 ml. Add 1 drop of 0.1 N hydrochloric acid, and electrolyze with a current of 1 ampere for 30 minutes. If no lead peroxide appears after 2 or 3 minutes indicatin the absence of lead, add 10 ml. of lead nitrate soldtion (O.l6%? and continue electrolysis for the specified time. Add 8 ml. of dilute sulfuric acid (1 to 1) and plate until the deposition of copper is complete, as shown by rinsing the beaker with a jet of water and noting no furthen deposition of copper on the newly exposed platinum. Raise the electrodes out of the electrolyte and wash by immediately substituting for the latter B beaker containing 200 ml. of distilled water. Reserve the electrolyte, A. Rinse the cathode by immersion in 2 separate portions of alcohol and dry a t 110” C. for 2 minutes. If lead is to be determined, dry the anode a t 110” C. for 30 minutes. Allow the electrodes to cool in a desiccator and weigh. Dissolve the deposits in dilute nitric acid (2 to 3) containing a few drops of hydrogen peroxide (30%). Rinse the electrodes with distilled water and ignite a t red heat. Cool in a desiccator and reweigh. DETERMINATION OF TIN. Transfer electrolyte A to a platinum dish of 300-ml. capacity, add 10 ml. of dilute sulfuric acid (1 to 1) and 5 ml. of hydrofluoric acid (48%), and evaporate to fumes of sulfuric acid. Rinse down the dish with a jet of water, warm until salts are in solution, and evaDorate aeain to fumes of sulfuric acid. Dissdve the salts in about 50 ml. of water and transfer io a 250-ml. beaker. Adjust the volume to 125 ml., heat to boiling, and introduce hydrogen sulfide for 30 minutes. Add some macerated paper pulp and filter the tin suffide on an 11-cm. No. 42 Whatnian paper. Collect the filtrate in a 400ml. beaker. Wash the precipitate and paper a few times with dilute sulfuric acid (1 to 100) saturated with hydrogen sulfide. Reserve the filtrate, B, for the determination of iron and nickel. Return the paper and precipitate to the original beaker, digest with a mixture of 20 ml. of sulfuric acid (sp. gr. 1.84) and 30 ml. of nitrjc acid (sp. gr. 1.42) until all orgaxuc matter is destroyed 8s indicated by the absence of any charring, and evaporate to fumes of sulfuric acid. Cool, rinse the cover glass and beaker with a jet of water, and again evaporate to fumes of sulfuric acid. Add 30 ml. of water and transfer to a tin reduction flask (Figure 1). Add 75 ml. of hydrochloric acid (sp. gr. 1.18), 8 grams of test lead, and 10 ml. of ferric Figure 1. Reduction chloride solution (1.5%). Dilute to Flask
42
INDUSTRIAL AND ENGINEERING CHEMISTRY
250 to 300 ml. and paw a slow stream of carbon dioxide through the solution a t the rate of 70 to 80 ml. per minute. With the carbon dioxide passing through the solution heat to boiling, and boil for 30 minutes after the yellow color due to ferric iron has disappeared. At the end of this period slightly increase the flow of carbon dioxide and immerse the bask in an ice bath. When the solution has cooled to about 5" C., remove t,he condenser, add 5 ml. of soluble starch solution (l.O%), and titrate to the appearance of a permanent blue color with standard potassium iodide-iodate solution (1.12 grams of potassium iodate and 12.0 grams of potassium iodide in lo00 ml. of water. Standardize thk solution against pure tin which has been reduced with lead in the usual manner). Continue the flow of carbon dioxide during the titration, and swirl the contents of the flask so as to ensure complete oxidation of tin. DETERMINATION OF IRON. To filtrate B from above, add 15 ml. of dilute sulfuric acid (1 to 1). Pass a stream of carbon dioxide through the solution a t the rate of 50 to 60 ml. per minute while bringing it to a boil, and continue boiling and addition of carbon dioxide for 15 minutes. At the end of this period, cool the solution rapidly to room temperature by immersion in an ice bath. When the solution hss cooled, stop the flow of carbon dioxide and titrate the ferrous iron, either potentiometrically or with o-phenanthroline as an indicator, with standard ceric sulfate solution (24 grams of ammonium ceric suifate in IO00 ml. of water containing 28 ml. of sulfuric acid. Standardize this solution against pure sodium oxalate). Reserve the solution, C, for the determination of nickel. DETERMINATION OF NICKEL. To solution C add 10 ml. of citric acid (20%) and neutralize with ammonia (sp. gr. 0.90), using nitrazine paper as an indicator. Make just acid with dilute hydrochloric acid (1 to 1) a d heat to 70" to 80" C. Add dimethylglyoxime reagent (1.0% in alcohol) in amount necessary to precipitate the nickel and then 10 ml. in excess. Neutralize with ammonia (sp. gr. 0.90) and add 2 drops in excess.
Table 1. Sample NO.
Results of Analysis of Bureau of Standards Bronzes
Found,
%
Average,
%
Certificate Value,
%
Determination of Copper 62
Found,
%
Average,
%
Certificate Value,
%
Determination of Iron 1.10 1.11 1.13 1.11 1.10 1.11 1.11
628
62b
0.79 0.79 0.78 0.79 0.78
Determination of Lead
0.79
0.81
Determination ~f Tin
62
62a
62b
0.29 0.29 0.28 0.29 0.29
0.29
0.27
Determination of Nickel 62
0.83 0.84 0.83 0.83 0.84 0.96 0.96 0.95 0.96
0.95
0.83
0.84
0.96
0.97
Table II. Lead Found after Initial Deposition and upon Replating from a PO Per Cent Nitric Acid Solution
Sample Weight Grama 2.000 2.000 2.000 2.000
(Standard 62a. certificate value 0.50% .. Pb) First Plate Replate Weight of Weight of PbOt Pb PbOa Gram 7% Gram 0.54 0.0120 0.0125 0.55 0.0121 0.0127 0.54 0.0120 0.0125 0.54 0.0120 0.0125
-
62b
Pb
% 0.52 0.52 0.62 0.52
Allow the solution to cool to room temperat,ure, and filter by means of vacuum on a weighed Gooch or sintered-glass crucible. Wash thoroughly with cool water to which a few drops of ammonia (sp. gr. 0.90) have been added. Dry at 120" C. for one hour, cool in a desiccator, and weigh. For large amounts of nickel, a drying temperature of 150" C. should be used. DETERMINATION OF MANQANESE. Transfer 1.000 gram of sample or other suitable weight containing not more than 10 mg. of manganese to a 4Wml. beaker. Cover and add 30 ml. of acid mix [lo0 ml. of sulfuric acid, 525 ml. of water, 123 ml. of phosphoric acid (85%), and 250 ml. of nitric acid]. After the first violent reaction has subsided, heat until complete solution is obtained and no more brown fumes are evolved. Remove from the hot plate andadd in order, 100 ml. of water, IO mi. of silver nitrate solution (0.8%), and 10 ml. of ammonium persulfate solution (25%). Heat rapidly to boiling and boil vigorously for 30 seconds but no longer. Cool to room temperature by immersion in tap water, add 75 ml. of water, and titrate potentiometrically with sodium arsenite solution (6.0 grams of arsenic trioxide and 15 grams of sodium hydroxide diluted to 525 ml. and saturated with carbon dioxide. Dilute to 5.0 liters). Analyze a standard bronze of known manganese content (containing a p proximately the same amount of manganese as present in the sample) to determine the titer value of the arsenite solution. DETERMINATION OF ALUMINUM.To a 2.000-gram sample contained in a 250-ml. beaker, add 25 ml. of dilute n i ~ i cacid (2 to 3). When solution is complete, add 15 ml. of dilute sulfuric acid (I to I). Evaporate to fumes of sulfuric acid, cool, nnse the cover glass and beaker with a jet of water, and warm until soluhle d t s are in solution. Evaporate again to fumes of sulfuric acid. Add 30 ml. of water to dissolve the soluble saits, dilute to 150 ml., and transfer to a mercury cathode cell. Electrolyze until the blue color due to copper has disappeared. Reduce the acid concentration of the solution by the addition of 10 ml. of ammonia (sp. gr. 0.90), rinse down th? cell with a jet of water, and continue the electrolysis for 1 or 2 hours longer. Remove the solution from the cell and fi!ter through an 11-cm. So. 42 Wnatman paper. Add 5 or 6 drops of a saturated solution of sulfurous acid to the filtrate and boil for 2 or 3 minutes. Add 2 drops of methyl red indicator,'make just alkaline with ammonia (sp. gr. 9.90) and then add 2 drops in excess., Bring to a boil and filter with some macerated paper pulp on an 11-cm. No. 42 Whatman paper. Wash with a hot 2Q/, ammonium nitrate solution made just aikaline to methyl red with ammonia. Transfer the filter. paper and contents to a weighed platinum crucible and heat until all the carbon is destroyed. Moisten the contents of the crucible with 6 drops of dilute sulfuric acid (1 to 1 ) . Add 10 mi. of hydrofluoric acid, and heat on the hot plate untii no more fumes of sulfuric acid are evolved. Finally ignite at the full heat of the blaVt lamp for 15 minutes, cool in a desiccator, and weigh ns aluminum oxide. EXPERIMENTAL RESULTS
The results obtained by the use of this procedure are shown in Table I. National Bureau of Standards samples of manganese bronze were used to test the accuracy of the method. NOTES
62a
Vol. 17, No. 1
ON
PROCEDURE
It was noted by McCay (5)that during the electrolysis of a solution containing hydrofluoric acid, there was always some anodic attack and that platinum to the extent of 0.5 mg. would plate out on the cathode. He also observed that a plate of lead peroxide on the anode would prevent this attack. Contributing factors in the contamination of cathodic plates by platinum are time of electrolysis, current density, and concentration of hydrofluoric acid. Under the conditions recommended for the elec-
ANALYTICAL EDITION
January, 1945
Figure 2.
Setup for Obtaining Carbon Dioxide
trolysis-namely, 1% hydrofluoric acid solution, a current of one ampere for 4 hours, and a t least 2 mg. of lead present to protect the snode-not more than 0.1 mg. of platinum will be dissolved from the anode. The deposition of copper under the specified conditions is rapid, and for all purposes, complete. After combining the electrolytes from 8 copper determinations, a total of 0.6 mg. of copper was found. This represents B loss of 0.08 mg. or 0.004% of copper per determination for each 2.0000-gram sample.
Teblr 111. Tin Losses lncunrd after Redudion with Lead in the Presence of Copper %lb COPPS.
Ti0 Prasent
present ea C"PTiC Sulfate
Ti" Found
0.2046 0.1522 0.1125 0.0849 0.0383 0.0327 0.0399 0.0384 0.0362 0.6393
0.240 0.200 0.140 0.100 0.040 0.020 0.010 0.005 0.002 0.001
0.0833 0.0503 0.0344 0.0282 0.0158 0.0212 0.0339 0.0358 0.0355 0.0390
Tin Laat
Ratio of Tin Loat to Copper Present
0.121s 0.1059
1:1.98 1:1.89 1:1.79
0.0781 0.0557 0.0225 0.0115 0.0060
0.0026 0.0007 0.0003
1:1.77
1:1.78 1:1.74 1:1.07 1:1.92 1:2.sP, i:a.33
43
2GU" C. without noting any differencein weight. The contaminants of the lead peroxide deposit in the proposed procedure are manganese and fluoride. I n the analysis of 8 samples of Standard 62a, containing 1.51% manganese, it was found tbat on an average each lead peroxide deposit was contaminated with 0.15 mg. of manganese. Mecay (6,B) found defioite evidence that fluoride in some form is present in the dried lead peroxide deposit. More accurate lead values may he obtained, as described by McCay (6,6), by trsnsfemng the anode with its lead peroxide deposit to a previously boi!ed %2 nitric acid solution, reversing the current for B few seconds, and then replating for one hour. Where the highest accurscy is desired, a third replate may be necessary. Table I1 shows results obtained using this procedure. It has been stated (8) that in the ionic condition some tin codeposits with copper during electrolysis of the latter. The presence of hydrofluoric acid prevents this contamination. Using the proposed procedure, the combined plates from 8 copper determinations of Standard 628 showed the complete absence of tin. I n the evaluation of tin by reduction with lead, the presence of copper is a serious source of error. Clarke (I) notes that a unit weight of copper causes the loss of about hslI s unit weight of tin. He explains this by assuming that cupric copper is reduoed to the metal by lead, and then plates on the latter. The couple thus farmed reduces tin to the metallic state, thus preventing reaction with the potassium iodide-iodate Teagent. Table I11 shows tin losses incurred when known amounts of stannic tin were reduced with lead in the presence of varying amounts of copper present as cupric sulfate. On the basis of the above facts, it is obvious tbat complete initial electrolytic deposition of copper is essential. Otherwise, undeposited copper will follow tin through the subsequent separations, causing low tin values. I n the usual case, there are no elements present in a bronze that interfere with the determination of iron after reduction with hydrogen sulfide. Lundell and Knowles (3)have stated that polythionic eompounds may form upon treatment with hydrogen sul6de. These compounds consume the oxidizing agent and cause high values. Using the recommended acid concentration during the reduction, no difficulty in this respect has been experienced at this laboratory. A rotating electrode apparatus for the deposition of copper and lead is preferred to others of the glass stirrer type, bemuse danger of contamination by iron due to hydrofluoric acid attack on the stirrer is eliminated. For the same reason, imn-free Vycor beakers sre used in preference to Pyrex. These beakers are remarkably resistant to the action of hydrofluoric acid. Some have been used in this laboratory for well over a year and, although somewhat etched, are still serviceable. The tin reduction 9ask shown in Figure 1 bas proved to be more convenient than the usual Bhole rubber-stoppered flask, and accuracy is not impnired. Figure 2 shows a convenient setup for obtaining the carbon dioxide needed for tin and iron determinations. ACKNOWLECGMENTS
The procedure used for washing the deposits avoids .undue dilution of the electrolyte. A solvent action on the cathode d e posit might be expected in the interval between removal of the electrolytic solution and the introduction of the beaker of wash water. McCay (6) statea that lead peroxide is not appreciably attacked by nitric, sulfuric, and hydrofluoric acids in the eoncentrations encountered in the electrolysis of copper m d lead. To determine if any copper were lost in the wash water, the washings of 8 copper determinations were combined. N o copper was found present. Examination of the results in Table I shows consistently high values for lead. Under normal plating conditions-that is, in nitric acid solution-many investigators have obtained high lead values, which tbcy have ascribed to occluded water. A t this laboratory lead peroxide deposits have been dried a t 110' and
Grateful acknowledgment is made to Louis Singer, formerly of the Naval Research Laboratory, for his helpful suggestions and interest in this work. L I E R A N R E CITED
(1) Clarke, 8. G., Analyst, 56,824 (1931). (2) Lundell. G. E. F., and Eowlea. E. B.. J . Am. CAW. 80% 43, 1660 (1921).
(3) Lundell, G. E.
P.,and Scberrer, J. A.. J. IND. ENO.Cmar., 14,
426.9 (1922).:
(4) McCay. L. W., J . Am. CAm. SOL,31,37841 (1909). (5) Ibid., 36, 2375-81 (1914). (6) McCay, L. W., ind Furman, N. H., IW.. 38,640-52 (1916). PP~ENTE before D the Division of Analytical and Miom Chernistnl at the 108th Meeting of tho A s r ~ a r c ~Canxmri n SOCIETY. New York. N. Y.
