Determination of Metallic Copper in Cuprous Oxide-Cupric Oxide Mixtures LOREN C. HURD AND ARTHUR R. CLARK, R o h m a n d Haas Company, Inc., Philadelphia, Pa.
pending upon the volume of reagent used and the time required to make the extraction. Cuprous and cupric oxides are soluble in a number of reagents which are without appreciable solvent action upon copper. However, when oxide mixtures containing finely divided metallic copper are dissolved in the salt solutions, a secondary reaction between the cupric or complex cupric ions and copper takes place. The metal is oxidized to a soluble monovalent form with the simultaneous reduction of an equivalent amount of divalent copper. Whereas this reaction may be so slow as to be of little consequence a t ordinary temperature, it is of significance a t the elevated temperatures required to dissolve all the cupric oxide contained in some of the refractory commercial samples. In an effort to decrease the solubility of metallic copper in solutions of the type suitable for extraction of oxide mixtures, an attempt was made to find a reducing agent which, when added to the salt solution, would reduce divalent copper to the cuprous state but not to metallic copper, and which would have no solvent action upon the copper itself. Various combinations of ammonium chloride, ammonium carbonate, and magnesium chloride with hydrazine sulfate, hydroxylamine hydrochloride, sodium arsenite, and other reducing agents were investigated. It was found that in an atmosphere of carbon dioxide, a hot 20 per cent solution of ammonium chloride containing 5 per cent of hydroxylamine hydrochloride would dissolve cuprous and cupric oxide with but slight action upon coarse metallic copper. However, when the copper was introduced in the form of a 325-mesh powder, the action was marked and losses of as high as 10 mg. of copper per 100 mg. of dissolved cupric oxide were not uncommon. Solutions containing hydrochloric acid behaved in a similar manner. Ammoniacal ammonium chloride solutions containing either hydrazine sulfate or hydroxylamine hydrochloride could not be used because when hot they react with both cuprous and cupric copper to produce metal. It was found that the cuprous oxide could be quantitatively extracted from oxidemetal mixtures with cold ammonium hydroxide containing ammonium carbonate. Only a very small amount of cupric oxide passed into solution and, in the absence of air, the copper was practically insoluble. The addition of a small amount of hydrazine sulfate was found to be effective in further reducing dissolution of the metal. If the extraction was carried out in an atmosphere of carbon dioxide, the gas served to prevent air oxidation and, as a result of partial interaction with the ammonia, to accelerate solution of cuprous oxide.
Cuprous oxide is soluble in cold aqueous ammonia, whereas cupric oxide is but slightly soluble and metallic copper insoluble. The addition of hydrazine sulfate to the reagent tends to reduce any divalent copper entering solution and prevents interaction of cupric copper and metal. If the extraction be carried out in carbon dioxide atmosphere, the metallic copper-cupric oxide mixture may be isolated and the metal determined by direct solution in acid ferric chloride, followed by titration with potassium dichromate.
T
HE assay of commercial cuprous oxide, according to
present approved and accepted methods, involves the direct solution of a weighed sample in acid ferric chloride. The ferrous iron produced during the oxidation of the monovalent copper is determined by titration with a standardized solution of potassium permanganate (1, 7 ) . Inasmuch as metallic copper is also soluble in the reagent, this, if present, is calculated t o cuprous oxide in the analysis. It is thus theoretically possible for an equimolar mixture of cupric oxide and metallic copper to be reported as pure cuprous oxide. The influence of copper on the determination has been previously noted (g). Le Blanc and Sachse (5) analyzed mixtures of cupric and cuprous oxide by allowing the samples to react with hydrochloric acid solutions of potassium iodide. The iodine liberated as the result of the oxidation of the iodide by the cupric salt was determined in the usual manner. When the method was applied to oxide-metal mixtures of the type under consideration, it was found that the copper was oxidized by the liberated iodine a t such a speed as to render unreliable an analytical method utilizing this reaction. The direct extraction of both oxides by means of a sodium cyanide solution was advocated by Bonner and Kaura ( 3 ) . When applied t o oxide mixtures containing copper in as fine a state of division as found in commercial samples, serious copper losses have been encountered. Solution of the metal probably takes place according t o both of the following equations: CU" 7 - C u f + ~ C U" 2CN-
'
+ 2Cuf + 2Hz0 +(CUCN)~+ 20H-
+ HZ
It has been observed that copper losses vary directly with the amount of cupric oxide in the sample and the volume of reagent employed. The silver sulfate-sulfuric acid method (6) involves a preliminary extraction of metallic copper by boiling the sample with a saturated silver sulfate solution. The residue, consisting of the two oxides mixed with metallic silver, is thoroughly washed and the dissolved copper determined in an aliquot of the filtrate. The method leads to erroneous results because during the extraction finely divided cuprous oxide in contact with the hot sulfate containing solution undergoes disproportionation. The metallic copper produced reacts with excess silver sulfate and is thus dissolved. Apparent copper recoveries are invariably high, the magnitude of the error de-
Preparation of Solutions EXTRACTION SOLUTION.Six grams of c. P. hydrazine sulfate were added to 1 liter of aqueous ammonia (sp. gr. 0.90). FERRIC CHLORIDE.One hundred and fifty grams of FeCl8.6Hz0 and 300 ml. of hydrochloric acid (sp. gr. 1.2) were dissolved in 800 ml. of air-free carbon dioxide-saturated water. Two grams of barium di henylamine sulfonate, INDICATOR. 50 ml. of carbon dioxide-saturated distilid water, and 5 grams of sodium sulfate were shaken until a uniform suspension of barium sulfate was obtained. The solution was diluted with 50 ml. of water and allowed to settle. When clear, the supernatant liquor was decanted through a filter and preserved in a dark bottle. The barium diphenylamine sulfonate was obtained from Eastman Kodak Company. PHOSPHORIC ACID. Ortho, 85 per cent reagent, A. C. S. specifications. 380
SEPTEMBER 15, 1936
ANALYTICAL EDITION
381
POTASSIUM DICHROMATE. 0.1 N solution prepared by dissolving 4.903 grams of reagent quality potassium dichromate in water and diluting to 1liter. WATER. Distilled water was boiled vigorously for several minutes and allowed t o cool in an atmosphere of carbon dioxide. A slow current of the gas was passed continuously through the storage bottle.
gram sample for cuprous oxide are of convenient size. In this case, one-fifth of the volume of dichromate used in the determination of metallic copper is subtracted from the total titration of the smaller sample to give the volume of dichromate actually equivalent to the cuprous oxide in the sample.
Apparatus
Results of Analysis
With the possible exception of the filter tube, no unusual apparatus is required for the determination.
The method as outlined above was checked on a variety of cupric oxide, cuprous oxide, and copper combinations under varying conditions. I n Table I are to be found the results of one complete series of determinations upon such mixtures.
The filter is similar to that used by Geilmann and Weibke (4), and consists essentially of a 55-mm. filter tube of the type used for small Gooch crucibles. In the opening is placed a perforated porcelain button which is seated at right angles to the stem. An asbestos pad is built up over the button and securely set by tamping with a glass rod. The filter must be packed in such a manner that the tube may be held in an inverted position without dislodging either the disk or the pad. It has been found that a tube about 60 X 25 mm., with a stem of 110 mm., is a convenient size. A 20-mm. Gooch crucible button serves t o support the asbestos pad.
Procedure A sample of suitable size is weighed out on a small watchglass, and the glass and contents are placed in a dry, widemouthed 250-ml. Erlenmeyer flask. If the material is an electrolytic roduct low in copper, it is advisable to take a 1-to 2-gram sampE. If it is from a “thermal process,” the percentage of copper is usually large and a smaller sample will suffice. The air in the flask is displaced with carbon dioxide (15 to 20 cubic feet per hour) and 10 ml. of ethyl alcohol are added to dissolve any oil present in the sample. Without interrupting the flow of gas, 150 ml. of extraction solution are added. Any lumps of oxide are broken up with a stirring rod. Violent agitation should be avoided. The carbon dioxide inlet should be about 5 cm. (2 inches) above the surface of the liquid. The time required for complete solution of all cuprous oxide varies between 1 and 5 minutes, depending upon the amount and character of the sample under inve&igation. When the cuprous oxide has completely dissolved, as evidenced bv the total disamearance of red Darticles. the filter is connected t6 a suction and slowly lowered into the flask. As soon as the bulk of the solution is removed, the flask is rinsed with carbon dioxide-saturated water and the filtration and washing are continued. Five or six 100-ml. portions of wash water will suffice to remove all the original extraction solution containing the dissolved cuprous oxide. The filter is then disconnected and the ad and contents are ushed back into the flask with a glass rod. Fifteen milliliters of ferric chloride solution are added and the flask is warmed to dissolve the cupric oxide-copper residue. When all articles have disappeared, the solution is cooled to below 40’ and 10 ml. of phosphoric acid and 3 drops of indicator are added. Dichromate solution is run into the flask until the end point, a change from pea green to intense purple, is reached.
8.
The result is calculated according to the following equation:
N
KzCrZO7
X ml. X 0.03179
wt. of sample
=
% cu
The percentage of cuprous oxide in the sample may be determined by dissolving a 0.2-gram sample in ferric chloride and titrating the ferrous iron produced with potassium dichromate in the manner described. It is essential that solution of the sample be carried out in an atmosphere of carbon dioxide or other inert gas. From the volume of dichromate solution equivalent to both the cuprous oxide and copper, the true percentage of cuprous oxide in the sample may be calculated according to the following equation:
wt. of sample
X
The calculation of the result is simplified if the sample taken for the copper determination be a simple multiple of that used in the oxide analysis. I n actual practice it has been found that a 1.000-gram sample for metallic copper and a 0.2000-
TABLEI. RESULTSOF DETERMINATIONS No. 1 2
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
Weight Taken Cu CuO Cup0 Gram Gram Gram .... 1.000 .... 2.000
.. .. ..
0.0297 0.0582 0.1079 0.0962 0.0985 0.1041 0.0994 0.1022 0.1000 0.1024 0.1013 0.1001 0.1010 0.1009 0,1045 0.0969 0.1064 0.1029 0.1017 0.1023 0.1004 0.0995 0.1035 0.1023 0.1009 0.1078 0.1001 0.0993 0.1049 0.1034 0.1010
...
.... .... .... .... .... .... .... ....
... 0:030
0.060 0,100 0.300 0.750
...
... ... ...
... 0:050
0.050 0.250 0.050 0.150
...
0.4000 0.2000 0.1000 0,0990 0.2000 0.1500 0.1000 0.1000 0.4000 0.9000 0.3000
.... .... ....
o:iii
....
0.150
...
0: 050 0.050 0.1000 0.050 0.100 0.400
0.4000 0.3500 0.7000 0.0200 0.6000 0.3000 0.0600 0.1000
Copper Found Gram 0.0024 0.0045
0.0291 0.0581 0.1070 0.0956 0.0986 0.1032 0.0984 0.1011 0.0997 0.1020 0.1006 0.0999 0.1007 0.1000 0.1048 0.0966 0.1068 0.1030 0.1022 0.1023 0.1005 0.0992 0.1033 0.1015 0.1000 0.1079 0.0992 0,0988 0.1040 0.1032 0.1000
Error Gram
...... ......
Remarks 0.24 Cu 0.22% Cu Extrac- Voltion ume Min. MI.
-0.0001 -0.0006 - 0 . 0009
-to. -0.0006 0001 -0.0009 -0.0010 -0.0011 -0.0003 -0.0004 -0.0007 -0.0002 -0.0003 -0.0009 +0.0003 -0.0003 +0,0004 +o ,0001 + O . 0005 0.0000 +O.OOOl -0.0003 -0.0002 -0.0008 +0.0001 -0.0009 -0.0009 -0.0005 -0.0009 -0.0002 -0.0010
1 3 5 1 3 5 3 3 1 3 5 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
... ... ...
... ... ...
.. .. .. ... ... ... ... ... ...
100 150 200 300 100 100 100 100 100 100 100 100 100 100 100 100 100
TABLE11. ANALYSISOF COMMERCIAL SAMPLES OF CUPROU~ OXIDE Sample No.
CuzO Present
“CuzO” Direct
Cu Found
%
%
%
la
98.68
2m
104.20
10.38 10.44 11.84 11.84 1.27 1.29 9.54 9.64 0.26 0.24 0.22 0.22
75.16 75.15 77.43 77.42 85.98 85.90 77.97 78.05 95.00 95.01 6.49 6.46
3m
88.84
4m
99.48
5L
95.61
6T
6.92
The cuprous oxide used was a commercial grade electrolytic product. The cupric oxide was a 325-mesh screen fraction from reagent quality material. The metallic copper was 325-mesh electrolytic copper powder which had been previously extracted with the ammonium hydroxide- hydrazine sulfate solution, washed with water, alcohol, and ether, and dried in a vacuum desiccator. Results are corrected for copper contained in the cuprous 100 = % CUZO oxide used in the experiments. The errors are of about the same magnitude, irrespective of the amounts of material taken or the volume of extraction solution used. It was found that, if the ammonium hydroxide-hydrazine sulfate solution was allowed to stand in contact with the samples for more than 10 minutes, the
4
382
INDUSTRIAL AND ENGINEERING CHEMISTRY
loss in copper sometimes amounted to more than 2 mg. In one experiment, the reagent was allowed t o act upon a mixture of 0.4 gram of cupric oxide, 0.3 gram of cuprous oxide, and 0.1 gram of copper for 1 hour. At the end of this time, 0.0050 mg. of copper had dissolved. Care must be taken not to allow the extraction solution to become saturated with carbon dioxide. If the gas inlet to the flask be placed beneath the surface of the liquid, solubility errors will be increased. Fifteen determinations of metallic copper made upon a sample of electrolytic cuprous oxide indicated a n average value of 0.25 per cent, with a maximum deviation of 0.01 per cent and an average deviation of 10.006 per cent. The same number of determinations on a sample of “thermal process” cuprous oxide yielded an average value of 1.07 per
VOL. 8, NO. 5
cent, with a maximum deviation of 0.02 per cent and an average deviation of h0.008 per cent.
Literature Cited (1) Am. SOC. Testing Materials, Standard Method of Routine Analysis of Dry Cuprous Oxide, D-283-33. ( 2 ) Ibid., Standard Specifications for the Toxic Ingredients in AntiFouling Points, D-277-31. (3) Bonner, W. D., and Kaura, B. D., IWD. E m . CHEX, 19, 1288 (1927). (4) Geilmann, W., and Weibke, F., 2. anorg. allgem. Chem., 199, 120 (1931). (5) Le Blanc, M., and Sachse, H., Ann. Physik, 11, 727 (1931). (6) Scott, W., “Standard Methods of Analysis,” 4th ed., p. 208, New York, D. Van Nostrand Co., 1927. (7) U. S. Navy Department Specifications, 52 C4b, 1935. RECEIVED August 20, 1936.
Quantitative Determination of Cadmium and Lead in Zinc Using a Grating Spectrograph with a Sector Disk HARRIS M. SULLIVAN, The Pennsylvania State College, State College, Pa.
T
HIS work was a n attempt to determine the possibility of using a replica grating spectrograph for making a quantitative determination of metallic impurities in compounds. The specific problem a t hand was the quantitative determination of cadmium and lead impurities in zinc. It was desired to take a specimen of unknown content and, by a simple procedure requiring approximately 15 minutes, excite the spectrum of the specimen, obtain a spectrogram, and from this spectrogram obtain the quantity of the impurities present. A method suitable for commercial use was desired.
A typical spectrogram is shown in Figure 1. Assuming the percentage content of the element present to be directly proportional t o the intensity of its characteristic lines for small percentages and the blackening of the film to vary logarithmically with the intensity falling upon the film, then the lengths of the lines produced by different percentages of a n element plotted against the percentage of the element should result in a curve which is a straight line. The curves were actually found to vary slightly from straight lines, as seen in Figure 2 .
The grating is mounted in the Rowland fashion, with the cam-
The arc consists of two vertical graphite electrodes, which must be of the purest graphite and approximately 0.6 cm. (0.25 inch) in diameter. The lower (positive) electrode is drilled with a 0.39-em. (0.156-inch) drill to a depth of 0.6 cm. (0.25 inch) and the sample under investigation is stuffed into this basin. This method of excitation of the spectra of slowly volatilizing substances is very effective because of the high temperature reached by the carbon arc. The current through the arc was about 5 amperes and the voltage supply 220 volts direct current. The voltage drop across the arc was 40 volts and the arc gap 1 cm.
era fixed t o photograph the first order of the visible range. It is posqihle, by rotating the grating about its vertical axis, to obtain
wave lengths from 10,000 A. to 2100 A,, the ultraviolet just outside the visible range being the most useful. The logarithmic sector disk is placed as near the slit as possible, and the mounting made stigmatic by placing the arc at the focal center of a convex lens, thus rendering a parallel beam of light on the slit. The sector disk is caused to rotate at a speed of 300 r. p. m. and is adjusted so that approximately 3-mm. length of the 16-mm. slit is left open at all times. The remainder of the slit opening is varied during the time of exposure as the sector disk rotates in front of it. The variation of time along the slit causes the lengths of the lines on the film t o vary according t o the intenaity of the line.
FIGURE1. SPECTROGRAM
It is essential in this type of work that the current and voltage drop across the arc, and consequently the energy consumed by the arc, remain constant. An inductance may be placed in series with the arc and resistance t o stabilize the arc c u r r e n t . Any other proved method of arc excitation of the spectra of the elements should prove as satisfactory as the one used here. Because sulfates are stable in the arc, the sulfate form of the sample was used for these tests. Any metal sample may be put into the sulfate form by first dissolving the sample in concentrated nitric acid, then adding concentrated sulfuric acid and evaporating the solution to dryness under a hood. After the residue has comdetelv dried. it i s g r o u n d i n m o i t a r and
