Determination of Copper and Nickel in Steels Determination of Copper by Electrodeposition and Nickel by Cyanide Titration LOUIS SILVERMAN, WILLIAM GOODMAN, AND DEAN WALTER United States Navy Chemistry Laboratory, Munhall, Penna.
I
N A R E C E N T paper Frediani and Hale (1) presented a
If after the appearance of copper the electrolyte is shaken until the plate dissolves and after another hour of electrolysis the electrolyte is removed, the percentage of ferrous iron in the electrolyte is in the neighborhood of 95. Thus, copper is deposited in a solution containing a preponderance of ferrous ion. Volatilization of chromium by hydrochloric acid (2) has no important effect.
method for the electrolytic determination of copper in ferroalloys, wherein the interference of the iron-nitric acid combination is eliminated by temperature control. Unfortunately, a special cooling cell is required. The twofold purpose of the present paper is t o electroplate copper in steel without the use of special apparatus and t o titrate nickel without previous separation by dimethylglyoxime. When a large number of determinations are to be made simultaneously, with no special accommodations other than the usual electrolytic board of ten t o thirty electrode units, the procedure outlined here may be used for both copper and nickel in the same steel sample.
TABLE 11. ANALYSIS O F %RESIST STEEL Thiosulfate Method ( 8 ) Sample 1 Sample 2
% Carbon Si1icon Manganese Phosphorus Sulfur Kickel Copper
Experimental Experiments were performed with a steel comparable t o Bureau of Standards No. lOla (18 er cent chromium, 9 per cent nickel), a steel containing sma! amounts of chromium and nickel, and finally a steel containing 1 per cent chromium, 1 per cent copper, and 1 per cent nickel. Steel samples varying from 0.1 to 2.0 grams were used with 0.020 gram of added copper, with and without added glacial phosphoric acid. For the nickel determinations a special steel of the Ni-Resist type (6 per cent copper, 14 per cent nicke!, and 3 er cent chromium) was used. The nickel was determined in e!t copper-free electrolyte, after oxidation of ferrous iron, by cyanide titration.
....
.. ....
6; i 4
Proposed Method Sample 1 Sample 2
%
.. .. .. .. ..
6:08
% 2.54
2.25,228 1.36 0.110 0.065 13.5 6.13 6.15
% 2 . 6 8 , 272
1.81, 182
1.15 0.12
0,083 13.4 6.06
Procedure
Ni-REsIsT STEELS. Weigh 2.500 grams of steel, transfer to a tall-form 300-cc. beaker, add 25 cc. of mixed acid (3 parts of hydrochloric acid, 1 of nitric acid, and 4 of water), and set on a warm plate. After solution is complete, add 30 cc. of technical (70 per cent) perchloric acid and heat to fumes of perchloric acid oxidizing chromium to chromic acid and graphitic carbon t o carbon dioxide. Filter into a 250-CC.volumetric flask, wash the silica OF COPPER IN SYNTHETIC SOLUTIONS with hot (1to 99) sulfuric acid, then with water, ignite, and weigh TABLE I. DBTERMINATION (0.020gram of copper taken) as silica. -AB -,CMake the filtrate up to the mark and shake. Transfer 20 cc. Time Time Time (0.20 gram) to a 400-cc. beaker and determine manganese and f OP for for .. .~ chromium (4). Transfer 100 cc. (1.00 gram) to a tall-form 300-cc. appearappearappearance ance ance beaker and determine phosphorus. of Copper of Copper of Steel Copper Transfer 100 cc. (1.00 gram) to a tall-form 300-cc. beaker, add Taken founda copper found" copper found4 copper (1 to 1) ammonium hydroxide until a permanent precipitate Grams G r a m >win. Gram Min. Gram iMin. forms, and add (1 to 1)sulfuric acid to dissolve the precipitate and 0 0.020 0 0 0.020 0.020 0.1 then 4 cc. in excess. Add 5 CC. of glacial phosphoric acid, and 0 0.020 0 0 0,020 0.020 0.2 electrolyze without stirring. Use an impressed voltage of about 0 0.020 0 0 0.020 0.020 0.3 0 0 6 volts and 0.6 ampere for about 2 hours on platinum electrodes. 0.020 0 0,020 0.020 0.4 0 0.020 15 5 0.020 0.020 0.5 Remove the electrolyte, wash the copper plating with water, dry, 0 20 0.020 0,020 5 0,020 0.6 and weigh. 0 25 0.620 10 0.020 0.020 0.7 Transfer the electrolyte to a 250-cc. volumetric flask, dilute to 0 25 0,020 10 0,020 0,020 0.8 25 5b 0,020 0,020 20 0.020 0.9 the mark, and shake. Transfer 50 cc. (0.20 gram) to a 400-cc. 106~0 25 0,020 Dark plate 0.020 1.0 beaker, add 10 cc. of (1 to 1) sulfuric acid and 20 cc. of 8 per cent 2,0 c 30b, 0 0.019 Dark plate 2.0 ammonium persulfate solution, stir, and heat to decompose exA. Plain steel p l u s 0.020 gram of copper. Dissolve in aqua regia, fume cess persulfate. Cool, and determine nickel by cyanide titration with perchloric acid, neutralize with ammonium hydroxide, acidify, and add ~
~
(4).
4 cc. of (1 t o 1) sulfuric acid excess. B. Same as A, b u t 2 cc. of glacial phosphoric acid added. C . 18 Cr-8 Ni steel, treated as in A. 0 0.020 + 0.0002 ram b 5 cc. of glacial p%osphoric acid added after 5 minutes. 0 Stirred, incomplete. d Intermittent sturing over 4 hours.
COPPERAKD NICKELIS STEELS. Dissolve 1.00 gram of steel in 20 cc. of mixed acid, add 15 CC. of technical (70 per cent) perchloric acid, and heat t o boil out the nitric and hydrochloric acids. Continue until the perchloric acid condenses on the underside of the cover glass. Cool, add 50 cc, of water, shake, boil out free chlorine, and cool. Add (1 to 1) ammonium hydroxide until a permanent precipitate forms, acidify with (1 to 1) sulfuric acid, and add 4 cc. in excess. Add 5 cc. of glacial phosphoric acid, and electrolyze without stirring. Use an impressed voltage of 4 volts maximum for copper less than 0.01 gram, 4 to 8 volts for copper above 0.01 gram, and 0.8 ampere. After 2 hours remove the electrolyte, wash the copper plating, dry, and weigh. To the electrolyte add 10 cc. of (1 to 1) sulfuric acid and about 50 cc. of 6 per cent ammonium persulfate solution, stir, and heat to destroy any excess persulfate. Cool. Test with permanganate, and oxidize any ferrous ion that may be present. Determine nickel by cyanide titration (4).
Results Table I shows that 20 mg. of copper may be deposited from steel solutions under the conditions noted. Copper appears sooner from electrolytes that contain phosphoric acid than from those that contain only sulfuric acid. Copper separates more slowly from chromic acid electrolytes. Table I1 shows that the method may be used to separate 6 per cent copper and 14 per cent nickel in steel. Table I11 shows that the proposed method may be used with steels containing 1 per cent copper and 1 per cent nickel, and with steels containing as little as 0.25 per cent copper.
Discussion The Frediani and Hale method for the determination of copper features low temperature in the presence of large
236
ANALYTICAL EDITION
March 15, 1942 r-
STEEL TABLE111. ANALYSISOF COPPER-NICKEL Thiosulfate Method (3)
Cu
Sample
S i
Proposed Method Manufacturers Cu Si Cu Xi
1 Bureau of Standards No. 106 2 Low chromium 3 Low chromium 4
c /u
/c
%
B
R
%
0.13
,, ,
0.14
.,
0:ZO
.. ..
0:26 1.07
1:73
5
1.12
..
6
1.16
..
7 18-8
,.
1:OS
..
..
..
0.20 0.13
1.10 1.0s 1.10 1.10 1.14 0.15
.
1:70
..
..
..
..
1.62 8.50
1.12
1.56
..
8.56
amounts of ferric ion complex and ammonium ions, whereas in the proposed method room temperature prevails and the order of the reaction must be: (1) reduction of all hexavalent to trivalent chromium, probably by the electrolytic production of ferrous ion (which would reduce dichromic acid), (2) complete reduction of ferric to ferrous ions in the immediate vicinity of the cathode, and (3) complete deposition of the copper. Stirring the liquid will prevent formation of the copper plate, or will redissolve it after it has formed. Using a potential source of 4 volts, the actual potential across the electrodes of an agitated solution is about 1.6 volts, while the copper deposits in a n unagitated solution only when the voltage drop is greater than 2 volts. Copper is deposited from electrolytes that show between 0.6 and 0.95 gram of ferrous ion. The as-
237
sumption is that, in an unstirred solution a protective coating of hydrogen gas forms and serves as a cause for overvoltage to permit deposition of copper and as a blanket to prevent resolution by the electrolyte. When phosphoric acid is present, copper begins to deposit sooner than in its absence. Manganese dioxide does not appear a t the anode. I n order t o procure bright adherent plates, if the copper is below 0.010 gram the voltage source (impressed voltage) must not be greater than 4 volts. Ni-Resist steels (6 per cent copper) give bright copper plates, but the results are about 0.02 per cent higher, on the general run of samples, than those obtained by the thiosulfate method (3). Seither manganese nor nickel has been detected in the copper plates. Nickel is easily determined in the electrolyte after oxidation of ferrous ion by persulfate or permanganate. Excess persulfate is destroyed by boiling, and even excess permanganate is avoided by ordinary precautions or additon of a sulfite. The paper neither affirms nor disaffirms the work of Frediani and Hale, since there are no points of common interest.
Literature Cited (1) Frediani, H.A,, and Hale, C. H., IND.ENG.CHBJM., ANAL.ED., 12, 736 (1940). (2) Lundell, G . E. F., and Hoffman, J. I., "Outlines of Methods of Chemical Analysis", p. 47, New York, John Wiley & Sons, 1938. (3) Silverman, Louis, IND. ENG.CHEX.,ANAL.ED.,12, 344 (1940). (4) Silverman, Louis, and Gates, O., Ibid., 12, 518 (1940).
Determination of Alcohol by Volume in Distilled Liquors Sources of Error L. C. CARTWRIGHT, Foster Dee h e l l , Inc., Brooklyn, N. Y.
P
ERSISTENT recurrence of relatively small but significant discrepancies between the results obtained in different laboratories in the determination of alcohol by volume on duplicate samples of distilled liquors led to a n investigation of the A. 0. A. C. official method for alcohol by volume (1, p. 172). This investigation disclosed a source of error inherent in the method, exclusive of any experimental errors. The A. 0. A. C. official method rovides that the specific gravity of a distilled liquor shall be getermined in air at 20/20° C. Alcohol by weight is determined by weighing 20 t o 25 grams of sample, diluting with 100 nil. of water, distilling nearly 100 ml., weighing the distillate, determining the specific gravity of distillate, at room temperature if desired, obtaining the corresponding percentage of alcohol by weight from the proper A. 0. A. C. tables, multiplying this figure by weight of distillate, and dividing by weight of Sam le taken. Alcohol by vol%me is determined by either of two methods. In Method I, sample and distillate are treated as described above, the percentage of alcohol by volume corresponding to the specific gravity of the distillate is obtained from the proper A. 0. A. C. table. the volumes of the samde and distillate are calculated from their'respective weights and specific gravities, and the percentage of alcohol by volume in the distillate is multiplied by the volume of the distillate and divided by the volume of the sample to obtain the percentage of alcohol by volume in the original sample. In Method 11, a 25-ml. sample is measured at room temperature and the distillate is made t o a volume of 100 ml. at the same temperature. The specific gravity of the distillate is determined at room temperature and the corresponding percentage of alcohol by volume is multiplied by 4 to obtain the percentage of alcohol by volume in the original sample.
The percentage of alcohol by volume in any mixture of ethyl alcohol and water varies with the temperature; therefore the temperature a t which a given mixture will have a stated percentage of alcohol by volume must be specified. The generally accepted standard of temperature for alcoholic concentration by volume is 60" F. or 15.56' C., and the A. 0. A. C. tables give percentages of alcohol by volume at this temperature. However, the ratio of the volumes of definite weights of any two aqueous solutions of ethyl alcohol of different alcoholic concentrations varies with temperature, and herein lies the inherent source of error in the A. 0. A. C. official method for alcohol by volume. I n both Methods I and I1 the volumes of the sample and of the distillate may be determined a t temperatures other than 15.56" C. Yet the true percentage by volume at 60' F. of ethyl alcohol in the distillate is multiplied by the inverse ratio of these volumes to obtain the percentage by volume at 60" F. of ethyl alcohol in the sample. The result is in error by an amount depending . upon the alcoholic concentrations of the sample and the distillate and the temperature at which the volumes of the sample and the distillate are determined. The calculated data presented in Tables I1 and 111 show that this inherent error is very substantial under conditions often prevailing in the determination of alcohol by volume by the A. 0. A. C. official method. I n order to show the magnitude of the inherent error over a wide range of conditions cdculations were made for a series of
