INDUSTRIAL AND ENGINEERING CHEMISTRY
Ami1 15. 1931
217
Electroanalytical Separations in Ammoniacal Fluoride Solutions I-Separation of Copper from Arsenic and Antimony’ N. Howell Furman FRICKCHEMICAL L A B O RORY, A ~ PRINCETON UNIVERSITY, PRINCETON, N . J.
A new procedure has been described for the elecHIS study originated Weighed amounts of pure trolytic separation of copper from arsenic and antiantimony and of arsenious from a consideration of the p r o b l e m of mony in ammoniacal fluoride solution. oxide were dissolved in 3 to Some qualitative observations have been made upon electrolytic deposits of cop5 CC. of 48 per cent hydroper contaminated with arthe rapidity of the oxidation of trivalent antimony by flueric acid and 25 cc. of senic and antimonv. It was persulfate under various conditions. nitric acid (1 volume of acid shown in preliminary experiof sp. gr. 1.42 and 4 volumes ments that a known weight of copper could be coated elec- of water). A measured volume of standard copper solutrolytically with arsenic and antimony, and the deposit could tion was added. Oxidation of arsenic and antimony was then be dissolved in a mixture of nitric and hydrofluoric completed by adding a moderate excess of potassium peracids, after which the procedure described in this paper gave sulfate (1 to 2 grams). A few of the oxidations were comcorrect results for the copper. pleted by boiling the strongly acid solution for 30 minutes. Ammoniacal solutions of quinquevalent arsenic or anti- Subsequent oxidations were effected by boiling the acid mony may, as is well known, be electrolyzed with currents solution 2 to 3 minutes, followed by immediate neutralizaas great as 5 to 10 amperes per square decimeter of cathode tions with ammonia. The efficiency of this procedure was surface, without deposition of arsenic or antimony a t the established by numerous qualitative tests of which the cathode. This fact has been made the basis of the separa- following is typical: A solution containing 0.12 gram of tion of a number of metals from arsenic and antimony, for trivalent antimony, 1.25 cc. of 48 per cent hydrofluoric acid, example, cadmium ( l a ) ,copper (Y), nickel (5), or silver (14) 1.25 cc, of concentrated sulfuric acid, and 1 gram of potasfrom arsenic, or cadmium (15), copper (11, 16) or silver (3) sium persulfate in 35 cc., gave a distinct qualitative test for from antimony. trivalent antimony after several minutes’ boiling. In one Methods which have been developed previously offer no instance a positive test was obtained after boiling for 20 simple scheme for the solution .and complete oxidation of minutes, and a further test after 25 minutes showed the oxidaarsenic and antimony when admixed with copper. Bosek (1) tion to be complete. A similar solution, previously neutralhas shown conclusivelythat the complete oxidation of antimony ized with ammonia, then cleared by adding the minimum with nitric acid is a matter of very considerable difficulty. amount of 6 N nitric acid, was boiled 3 minutes after adding A mixture of copper, arsenic, and antimony, whether 1 gram of the persulfate; the oxidation was then found to derived by electrolytic deposition or otherwise, may be be complete. The qualitative tests were made by the Rose dissolved in a mixture of nitric and hydrofluoric acids (9). method (2), and by treating the solution with hydrogen The oxidation of the last traces of trivalent arsenic and sulfide, which under these conditions gives no immediate antimony in such a solution may be effected very readily coloration or precipitate unless trivalent antimony is present. with potassium persulfate. This method has been studied Table 11-Separation bf Copper f r o m Arsenic a n d Antimony by McCay in connection with an investigation of the separaANTIMONY ARSENIC COPPER COPPER tion of arsenic from antimony (9). He found that some DETN. PRESENT PRESENT PRESENT FOUND^ ERROR Gram Gram Gram Gram Mg. 20 to 30 minutes of boiling of the acid solution with an excess -0.2 0.2044 0.2042 0.1805 .... of persulfate would complete the oxidation of arsenic and -0.1 0.2043 0.4070 0.2044 .... 0.2047 $0.3 0.3530 0.2044 .... the antimony. The author has found that the oxidation 0,1997 $0.5 0.2970 0.1992 .... goes-very rapidly in faintly acid solution; 2 to 3 minutes’ -0.7 0.1170 0.1992 0.1985 0.0758 +o. 1 0.2110 0.1993 0.1992 0.0987 boiling then suffices to complete the oxidation. -0.7 0.1972 0.3984 0.3977 0.1485
T
Experimental Procedure
The materials used in the separations were of known purity, being part of a large stock that had been tested in previous investigations (4, 10). In connection with these previous studies it was shown that antimony is not reduced during the electrolysis of an ammoniacal fluoride solution of potassium antimoniate. Kitric acid solutions of pure electrolytic copper were prepared and the metal was determined by electrodeposition. Table I gives the results. Table I-Determination NITRICACIDSOLN.
cc. 25 25 50 25 25 1
of Copper in Nitric Acid Solutions COPPERF O U N D Soh. I S o h . I1 Gram Gram 0.2047 0,1991 0.2044 0.1994 0.4086 0.3983 0.2044 Av. 0.2044 0.1992
Received March 4, 1931.
....
$0.2 0.3984 0.3986 0.1582 0.1058 Values corrected for small amounts of platinum dissolved from anode and deposited at cathode with the copper, In determinations 5 t o 8 a hard anode (platinum-iridium) was used and no weighable amount of platinum appeared in copper deposit. In the other cases from 0.2 to 0.7 mg. was found when copper was dissolved in nitric acid. Proof of presence of platinum was obtained by formation of potassium chlorplatinate, or by stannous chloride reduction test.
Copper was separated from the cold, strongly ammoniacal solution by electrolysis after the completion of the oxidation. The total volume was 100 cc., containing 5 to 10 cc. of ammonia of sp. gr. 0.90. The series of separations recorded in Table I1 was made with stationary electrodes; current density 0.1 to 0.3 amperes per square decimeter and 2 to 4 volts applied a t the electrodes. The solution was in a paraffined beaker, and covered with paraffked split cover glasses. Complete deposition occurred in 5 to 8 hours. A number of electrolyses were allowed to continue overnight (15 to 18 hours) as a matter of convenience. The copper deposits were carefully tested qualitatively for presence of antimony and arsenic. The tests were generally
ANALYTICAL EDITION
218
negative. In one case the residue obtained upon acidifying the sulfosalt filtrate with acetic acid, after removal of the copper sulfide, gave a coloration with hydrogen sulfide like that due to antimony; the color was not as intense as that produced by 0.01 mg. of antimony under similar conditions A series of rapid separations was made using current densities of 4 to 8 amperes per square decimeter of cathode at a voltage of 8 to 12. The anode (a platinum-blade stirrer) was rotated at 500 to 700 r. p. m. The copper was deposited completely in 35 to 45 minutes The results are shown in Table 111. Table 111-Rapid Separation of Copper f r o m Arsenic a n d A n t i m o n y ANTIMONY ARSEPIIC COPPER COPPER DETN PRESENT PRESENT PRESENT FOUND^ ERROR Gram Gram Gram Gram Mg. 1 0 2342 0 1992 0 1997 2 0 2021 0 3984 0 3977 0 1733 0 2094 0 1992 0.1987 -0 5 3 4 0 1028 0 1493 0 1992 0.1998 SO 6 5 0 1082 0 1511 0 3984 0 3981 -0 3 Corrected for platinum (cf note, Table I I ) , amounts found 0 2 to 0 7 mg
2: 7"
Q
In a subsequent series of determinations, shown in Table IV, both copper and antimony were determined. After the copper had been deposited, the nitrates and fluorides were expelled by evaporation with an excess of sulfuric acid. McCay (9) has shown that this operation may be done in a quartz dish when the antimony is to be determined volumetrically The reduction was effected by heating with
Vol. 3, No. 2
about 1 gram of roll sulfur a t about the temperature of boiling sulfuric acid (8), for 30 minutes. The antimony was then determined by titration with 0.05 N potassium permanganate solution which had been standardized against pure dry sodium oxalate (6). Table IV-Determination COPPER Present Found Gram Gram 0.1992 0.1989 0.3984 0.3986 0.3984 0 3989 0 1992 0,1991
of Both Copper a n d A n t i m o n y Present Gram 0.1211 0,0926 0.1536 0.0880
ANTIMONY Found Grnm 0.1109 0.0931 0.1531 0.0874
Literature Cited Boqek, J. Chem. SOC.,67, 615 (1895). Fresenius, "Qualitative Analysis," translated by Mitchell, p 362, Wiley, 1921. Freudenberg, Z. phyyik. Chem , 12, 109 (1893). Furman, J . Am. Chem. Soc., 40, 895 (1918). Furman, Ibzd , 42, 1789 (1920). McBride, Ibid., 34, 393 (1912). McCay, Chem.-Ztg., 14, 509 (1890). McCay, J Am. Chcm. S O C ,32, 1241 (1910); 86, 2380 (1914) McCay, Ibid., 86, 2375 (1914). iMcCay and Furman, Ibid, 38, 640 (1916). Puschin and Trechinsky, Chem - Z t g , 28, 482 (1904). Rose, Pogg. Ann., 3, 441 (1924). Schmucker, J . Am. Chem. Soc., 16, 195 (1893); 2. anoyg Chem , 6,199 (1894). Smith and Frankel, Am. Chem. J . , 12, 428 (1890). Smith and Wallace, Z. anorg. Chem., 4, 273 (1893). Smith and Wallace, J A m Chem SOC.,15, 32 (1893)
Graphical Tensile-Testing Machine far Rubber Threads' S. H. H a h n and E. 0. Dieterich B. F. GOODRICH Co., AKROX,OHIO
MOKG the many types of physical testing equipment which have been designed for or applied to the needs of the rubber industry, there has never appeared an entirely satisfactory graphical machine for performing tensile tests on small rubber samples, such as the threads and tapes used in making golf balls and elastic fabrics and cords. None 6f the common machines can be applied directly to the testing of single threads, and even tests on pieces of dumbbell shape are quite unsatisfactory, largely because the standard machines are comparatively insensitive a t loaelongations and tensions and also because they depend on the personal accuracy of an operator to observe several points along the stress-strain curve. The Schopper ring test is not entirely successful for tests on threads. Accordingly it appeared that such tests on light rubber threads could best be made on a curve-drawing machine, designed and constructed especially for the purpose. In many cases, the use of any other machine would have been impossible because frequent tests had to be run on single, cut threads from factory production and on samples taken from storage or from woven fabric.
A
General Design Requirements
Several rather severe restrictions on the design were iniposed by the nature of the samples to be tested. These are as follows: (1) The breaking strength of the smallest threads to be tested is comparatively low. A 50 X 50 gage thread, the smallest 1 Received September 20, 1930. Presented before the Division of Rubber Chemistry a t the 80th Meeting of the American Chemical 5ociety, Cincinnati, Ohio, September S t o 12, 1930
ordinarily cut, has a cross-sectional area of only 0.00258 sq. cm. (0.0004 sq. in.) and a breaking strength of less than 450 grams '(1 pound). At the same time the heavier threads require a maximum tensile force of about 2 kg. (4 pounds), so that a full scale range of 2.26 kg. ( 5 pounds) has t o be provided. (2) Elongations up to about 1000 per cent on a 5.08-cm. (2inch) gage length have to be accommodated in testing pure gum stocks. (3) A high degree of sensitivity as compared with the usual machine is reauired in the renion of 200 to 700 per cent elongation where the tension usually varies from about 40 to 700 grams (0.1 to 1.5 pounds). (4) Whatever the grips used, they must not allow the I'ength under test to increase by creep or slippage of the rubber, and they must secure the thread so the gage marks are in full view.
It was found possible to achieve the result desired by modifying a small 11.32-kg. (25-pound) Scott machine designed for graphical stress-strain tests on tire cords. Friction was reduced to a minimum by the use of rotating bearings of small diameter instead of sliding parts, by the elimination of the thread-pulley-counterweight arrangement on the pen motion, by substituting wires for the usual roller chain supporting the upper pulling head of the machine, by using a lighter pen pressure, and by the elimination of the usual ratchet for catching the balance wheel a t the breaking point of the sample. The full scale capacity of the machine was reduced to 2.26 kg. ( 5 pounds) with provision for doubling the range without change of ,intermediate scale divisions. At the same time, the chart length was not changed materially because a reducing motion provided a chart traverse only one-third that of the lower pulling head. Tests and almost daily use during the past eighteen months
