INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 16, No. 2
in most cases the per cent conjugation is much more than twice that in the CY form, Number of Conjugated Ethenylene Linkages and in one instance (sample 8) the per New or old Old New Difference, Old New Differ- o oTetal n~~gacent of conjugation of the 8 form is five 8SmPle method method method % method method once, % tion, % times as great &9 that of the highest a 1 0.0034 0.063 0.061 313 1.1 1.1 0.0 1.2 form. This result is not unexpected, in2 0.0031 0.059 0.057 1.7 1.1 1.1 0.0 1.2 3 0.048 0.26 0.23 13 0.73 0.70 4.2 0.98 asmuch as the tetrabromide used to form 4 0.0034 0.17 0.17 0.0 1.31 0.29 6.6 0.46 the 8-acid is B mixture of stereoiso6 0.021 0.76 0.76 1.3 1.2 1.1 9.1 1.9 6 0.030 0.77 0.75 2.7 2 1 2.0 5.0 2.8 mers which yield, on debromination, geo7 0.027 1.41 1.41 0.0 3.1 3.0 3.3 4.4 8 0.028 2.30 2.30 0.0 4.4 4.1 7.5 6.4 metrically isomeric acids (4, 11). It is 9 0.0034 0.098 0.096 2.1 3.3 3.3 0.0 3.4 possible, then, that one or more isomers, 10 0.031 1.6 1.6 0.0 3.4 3.2 6.2 4.8 more readily conjugated than the a-acid, are the cause of the high Dercentaee of conjugation in the &acids. The effect of A comparison of the isomeric acid factor (right-hand column the solvent on the isomerization is indicated in the results, and in Table 11) with the total per cent conjugation of the same permits the listing of solvents in the order in which they give samples as shown in Table IV shows a reasonable agreement beincreasing amounts of conjugation-methyl alcohol, pyridine, tween these two data with regards to relative values of the isopropyl ether, dioxane, and diethyl ether. Acetic acid is CY- and 8-acid types, the CY values being lower in all cases. not listed, since it may react with zinc during the debromination Debromination methods of isolation not only tend to conand reduce some of the ethenylene linkages. jugate the unsaturated bonds of linoleic acid but also produce LITERATURE CITED considerable amounts of octadecadienoic acids which do not (1) Bradley and Richardson, IND.ENQ.CHF~M., 34, 237 (1942). yield insoluble tetrabromides, as is indicated by samples 1 and (2) Brode and Patterson, J . Am. Chem. Soc., 63, 3252 (1941). 4 a3 compared with samples 5 to 10. The fact that sample 3 (3) Dinnwall and Thomson. Ibid.. 56. 899 (1934). ' oontains comparatively large amounts of the three and four (4) Fraikel and Brown, I b G . , 63,'1483(1941). (5) I b i d . , 65,415(1943). conjugation is probably accidental, since none of the samples (6) Frankel, Stoneburner, and Brown, Ibid., 65,259 (1943). of the 8-acid which have been through two debrominations have (7) Henne and Turk, I b i d . , 64, 826 (1942). as high a percentage of four double bond conjugation. The (8) Hulst. van der. Reo. trav. chim., 54,644 (1935). origin of the conjugation cannot be accredited to alkaline sapon(9) Kaufman, Baltes, and Funke, Fette u. Seifen, 45,302 (1938). ification (1, 10, 16),inasmuch as the crystallization sample has (10) Kerns, Belkengren, Clark, and MiUer, J . Optical Soo. Am.,31, 271 (1941). also been through the same treatment during the preparation (11) Matthews, Brode, and Brown, J . Am. Chem. Soo., 63, 1064 of the free acid from the oil. A recent publication of Henne and (1941). Turk (7), which reports the conjugation of diolefins with metallic (12) Miller, "Quantitative Biological Spectroscopy", Vol. I, p. 236, halides, perhaps affords the best explanation of the cause of this Minneapolis, Minn., Burgess Publishing Co., 1940. (13) Mitchell and Kravbill. J . Am. Chem. Soc.. 64. 988 (1942). conjugation, since zinc bromide is formed as one of the products (14j Mowry, Ph.D. d&sertstion, Ohio State University; Columbus. during the debromination and is probably responsible for the Ohio, 1941. shift in the position of the ethenylene linkage. (15) Mowry, Brode, and Brown, J. Biol. Chem., 142,671 (1942). The samples of 8-acids are the products of two debrominaTHIEis the 13th in a series of papers on the ohemistry of fatty acids. Othera tion treatments and as such should have about twice as much in the series have been published as follows: J . Am. Chem. Soc., 63, 1064 conjugation as the CY forms. However, the data indicate that (1941); 65, 259,415 (1943): J . B i d . Chem., 142, 671 (1942). Table
IV. Percentage Conjugation in Linoleic A c i d E m p l e s
I
Electrolytic Determination of Copper in Steel and Cast Iron W i t h a Supplementary Colorimetric Procedure for Certain A l l o y Steels WILLIAM S. LEVINE AND HENRY SEAMAN, 1461 Daly Avo., Bethlehem, Pa. Copper is determined electrolytically in the presence of ferrous iron with the use of an Alundum thimble as a diaphragm. The mmple is dissolved in dilute sulfuric acid and the copper oxidized by ferric sulfate or nitric acid. Satisfactory results have been obtained on carbon and low-alloy steels and cast irons b y direct weighing of the cathode. Steels containing much molybdenum, tungsten, or chromium require that the plating b e dissolved and the copper determined colorimetrically. The simplicity and the time required for a determination compare favorably with existing methods.
T
H E present A.S.T.M. (1) methods for the determination of copper in steel are the electrolytic or gravimetric and the thiosulfate-iodide volumetric. Lundell, Hoffman, and Bright (4) describe the thiocyanate-iodide volumetric and the colorimetric-ammonia methods for determining copper. All these methods require a number of time-consuming steps, and a more direct method of determining copper is desirable for routine work. Frediani and Hale (2) report an electrolytic method in which the copper is plated out without separation of the iron. The
iron is present as the ferric phosphate complex and a temperature of 10" C. is required. Silverman, Goodman, and Walter (8) describe another electrolytic method in which copper is deposited from a solution containing all the iron in the trivalent state. No agitation is employed. A voltage of 6.0 is used and about 2 hours are required for complete deposition. Sand (7) determines copper in steel by means of an internal electrolysis method. I n the method reported here, the copper is plated from a solution containing approximately 5 grams of ferrous iron in about 45 minutes. A voltage of 2.1 to 2.2 is used with a minimum of special equipment. SPECIAL REAGENTS AND SOLUTIONS
SULFURIC ACID,4%. Add 40 cc. of concentrated sulfuric acid to 960 cc. of water to make approximately 4% sulfuric acid. FERRICSULFATE. Place 100 grams of Fe2(S0&.zH20 in a I-liter beaker, add about 750 cc. of water and 50 cc. of concentrated sulfuric acid, and heat the mixture slowly with frequent stirring until the reagent has all dissolved. Cool and dilute to one liter.
February, 1944
A N A L Y T I C A L EDITION
SODIUMT H I O C Y A SOLUTION. Dissolve 5 grams of sodium thiocyanate in 100 cc. of water. SODIUM DIETHYLNATE
D ITHI0 CARBAMATE
SOLUTION, 0.2'%. Dissolve 0.2 gram of the reagent in 100 cc. of water. DILUTEAMMONIUM HYDROXIDESOLUTION. Mix 200 cc. of concentrated ammonium hydroxide with 800 cc. of water. PROCEDURE F O R C A R B O N STEELS AND CAST I R O N S
Use a 5-gram sample for steels containing less than 0.5% copper and a correspondingly s m a l l e r w e i g h t for those higher in copper, Place the sample in a 200-cc. t a l l - f o r m beaker, add 92 cc. of distilled water and 8 cc. o f concentrated s u 1furic acid, cover the Figure 1 beaker with a watch glass, and heat until the iron is dissolved. The insoluble residue remaining contains most of the copper in the sample. Wash down any residue on the sides of the beaker, heat the solution, and when it is boiling vigorously, add 5 cc. of the ferric sulfate solution. Continue the vigorous boiling for 5 minutes. This treatment oxidizes the undissolved copper in the residue to divalent copper. With a glass tube of small bore, transfer a small amount of the solution to a spot plate, and add a drop of the sodium thiocyanate solution to the test sample on the spot plate. If the resulting color is a bright cherry red, the oxidation is complete and the proper amount of excess ferric ion is present. If the resulting color is a pale pink, all the copper may not be oxidized. I n this case, add 3 cc. more of the ferric sulfate solution, boil 5 minutes, and retest. For most steels, one addition of the ferric solution will be sufficient. Filter the solution, now containing all the copper as the cupric ion, through a Whatman No. 7 paper into a tall-form 200-cc. beaker, wash the residue 5 times with cold water, and discard it. For routine work, the residue need not be filtered off. Dilute the filtrate to 150 cc. with distilled water and cool to a temperature around 15" to 18' C. in running cold water. The sample is now ready for electrolysis. The apparatus used for the deposition of copper is shown in Figure 1. A represents the 200-cc. electrolytic beaker containing the dissolved sample. It is placed on top of the wooden block, L. The power source is a 6-volt, 150-ampere motor generator, B . The voltage can be set to any desired value by means of a field rheostat. C is the usual platinum gauze cathode about 20 mm. in diameter, which has been accurately weighed. The anode, D, is a platinum wire about 100 mm. long and 1.0 mm. in diameter. It passes through a No. 0 rubber stopper, F , and into the Alundum thimble, Z (KO. 7338 R.A. 360), which serves as a diaphragm. The stopper is notched, G, to allow gases evolved a t the anode to escape. The anolpte, 4y0 sulfuric acid, is poured into the thimble through the small tube, K. Compressed air to keep the solution stirred enters through tube H . The electrodes are connected to leads from the motor generator. The beaker containing the solution is placed under the electrodes and 47, sulfuric acid is poured into the Alundum cell through tube K until i t begins to overflow through notches G . The overflow is caught in the beaker, which is then raised until the electrodes are immersed in the solution. The block, L, is placed under the beaker. The top of the beaker is covered with split watch glasses, the current turned on, and the voltage adjusted to 2.1 to 2.2. It is important to keep the voltage as close to this value as possible to obtain a bright deposit. Air is bubbled through the solution at a rate which provides the most vigorous stirring without the loss of any electrolyte. The rurrent flowing
81
through the circuit is about 0.1 ampere at the beginning and about 0.02 ampere when all the copper is plated out. The electrolysis is allowed to continue for about 45 minutes before testing the solution to see if all the copper has been deposited. The test used is a variation of the usual sodium diethyldithiocarbamate qualitative test for copper (6). With a glass tube of small bore, a portion of the solution is transferred to a depression on a spot plate. Three drops of concentrated nitric acid are added and the mixture is stirred until the resulting black color disappears. Two drops of concentrated phosphoric acid and then two drops of the sodium diethyldithiocarbamate solution are added. A brown color disappearing almost immediately on stirring to give a colorless spot indicates that all the copper has been plated out. If all the copper has not been plated out, the spot will be yellow in color and will fade after a few minutes. If copper is still present, the electrolysis is continued for another 10 minutes and retested. When all the copper has been plated out, the watch glasses are removed, the air stirring is cut off, and while the current is still flowing, the block of wood is removed from under the beaker. Then, while the beaker is lowered slowly, the cathode is washed carefully and thoroughly with water from a wash bottle to remove iron salts. The cathode is disconnected, swirled around in a beaker of mater for about 10 seconds, dipped in a beaker of methyl alcohol, the excess alcohol is shaken off and the cathode dried in a drying oven maintained a t a temperature of 65" C. for 5 to 10 minutes. When the electrode is dry, it is cooled to room temperature and weighed. The weight of the copper deposit times 20 equals the per cent of copper in the sample if a 5.0-gram sample is used. The procedure for plain cast irons low in copper is the same as for carbon steels. As a rule, more ferric sulfate will be required to oxidize the copper in cast irons than in carbon steels. On Bureau of Standards samples 115 and 5h, no ferric sulfate was used, since it was necessary to add about 15 drops of nitric acid when the sample was partially dissolved in order to hasten solution and prevent the copper from separating out in large particles. The nitric acid added provided sufficient excess of ferric ion. M O D I F I C A T I O N S OF PROCEDURE F O R HIGH-ALLOY STEELS
While the above procedure can be used for the majority of alloy steels, modifications have to be made for some. With steels containing more than 0.2y0 molybdenum, a small amount of a substance which is probably a hydrated molybdenum oxide (5') is deposited along with the copper. To get accurate results for such samples, the deposit is stripped with nitric acid and the copper determined colorimetrically as described below. When samples contain about 7% or more of molybdenum, a large quantity of the ferric sulfate solution has to be added before a sufficient excess of ferric ion is obtained. Hence, it is better to add 5 drops of conrentrated nitric acid a t a time to these samples to oxidize tho copper. About 15 to 30 drops are usually required. High-chromium and 18-8 steels are treated in the same manner as the plain carbon st,eels, except that when the steels are well decomposed, 5 drops of nitric acid are added to the hot solution and boiling is continued until the sample is dissolved. KO ferric. sulfate needs to be added to oxidize the copper because the nitric. acid used is enough to provide a sufficient excess of ferric ions. The electrolysis is allowed t o continue for 45 minutes after a deposit is first noticed. The spot test cannot be used ITith highchromium steels, because of the blue color of the solution. Tungsten steels are run the same as the high-molybdenum steels. To get accurate copper results for molybdenum, high-chromium, and tungsten steels, the electrode deposit is stripped with nitric acid and the copper determined colorimetrically in the following manner. The deposit is stripped off the electrode in the apparatus shown in Figure 2. A is an open-top, cylindrical separatory funnel, the tube being about 80 mm. long with an inside diameter of 25 mm. B is an ordinary test tube of 16-mm. outside diameter cut down to a height of 120 mm. It is partially filled with water and placed inside the separatory funnel. The electrode, C, is slipped over the test tube, and 1 to 1 nitric acid is poured into the separatory funnel until the deposit is covered by the acid. About 13 cc. of acid are required. The acid is left in contact. with the electrode for about one minute, the electrode being moved up and down occasionally to stir the solution. The stopcock is opened and the solution run into a 50-cc. flask. Into the separatory funnel is poured an equivalent volume of 1 to 4 ammonium hydroxide which is run into the same flask after being
INDUSTRIAL AND ENGINEERING CHEMISTRY
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in contact with the electrode for a minute. The electrode is washed a second time with dilute ammonium hydroxide. The solution is neutralized with concentrated ammonium hydroxide and 5 cc. are added in excess. It is cooled, diluted to the 50-cc. mark, and shaken well to mix. A portion of the solution is transferred to the glass cell of a CencoSheard-Sanford Photelometer and the intensity of the color developed is measured using a red Corning filter No. 245. The corresponding milligrams of copper present are obtained by referring to a curve constructed by plotting the per cent transmission against the mlligrams of copper present in a series of synthetic samples containing known amounts of copper &E cupric nitrate (6).
~~
n
Table 11. Initial Temp.
c. 12
A
C
DISCUSSION OF PROCEDURE AND RESULTS
+
Figure 9
+ 2Fe++
The oxidation is fairly rapid, although not instantaneous. The particles of copper must be in a fine state of subdivision in order to get rapid and complete oxidation. When the steel sample is dissolved as described, this condition is usually automatically met. The only samples encountered in which the copper particles were too large t o be oxidized by the regular procedure were standard samples 115 and 5h, both high in copper. Table Bureau of Standards Sample No. 130 140 19u 20d
1.
74
0
Some typical single results obtained by this method on Bureau of Standards samples are shown in Table 1. Duplicate samples check to within O . O l ~ owhen copper is below 0.5’%’,.
The reaction involved in the oxidation of copper by trivalent iron is Cu 2Fe++++C u t +
18 18 34 34 78
Determination of Copper in Iron and Steel
Cormer. Comer. Copper, Ele’oiro: EG&ro: Standard lytic-Gravi- lytic-ColoriValue, % metria, % metric, % o 0.165 0.16 0.16 0.025 0.03 0.03 0.161 0.17 0.16 0.165 0.16 0.16 0.267 0.26 0.26 0.20 0.20 0.20 0.166 0.17 0.17 0.060 0.06 0.06 0.029 0.04 0.04 0.074 0.08 0.07
Type of Steel Carbon steel Carbon steel Carbon steel Carbon steel 35s Carbon steel 65b Carbon steel 129 Carbon steel 16c Carbon steel 74 Cast iron 107 Cast iron N i = 0.807, Cr = 0:455 107 0.074 0.05 0.08 Cast iron, N i = 0.807, Cr = 0.455 115b 6.44 6.40 6 45 Cast iron, Ni = 15.89, Cr = 2.17 1156 6.44 6.45 6.45 Cast iron, N i = 15.89, Cr = 2.17 Il5b 6.44 6.60 6.45 Cast iron, Ni 15.89, Cr. 2.17 11511 1.46 1.41 ... Cast iron 100 0.124 0.13 0.13 Mn = 1.38 33b 0.114 0.12 ’ 0.11 Ni = 3.48 73 0.033 0.04 0.04 Cr = 13193 32 b 0.117 0.11 0.11 Cr 0.638, Ni 1.21 io0 0.059 0.11 0.10 Cr 3 0.997, V = 0.235 ,2b 0.100 0.11 O.llc Cr 0.46, Mo = 0.224 36 0.110 0.16 0.lld Cr = 2 3 2 &io = 1.01 111 0.122 0.13 0.13 Xi 1.’75,’Xlo = 0.215 106 0.142 0.15 0.15 Cr = 1.29, Mo = 0.164, A1 1.06 101A 0.051 0.06 0.06 Cr = 18.33, N i 8.99 132 0.15 0.28 0.16 Mo- 7.1, W = 6.3 Cr = 4.09, V = 1.64 50a 0.074 0.12 0.07 Cr = 3.52. V = 0.97. R- 18.25 a Values obtained by stripping electrodes of copper shown in adjacent oolumn and determining copper 8 8 described in procedure. b 0.6-gram sample used. C On replating 0.10% copper was obtained. d On replatin;, 0.11% copper was obtained.
- -
-
-
-
Vol. 16, No. 2
~
~
~~~~~
EKect of Temperature on Copper Deposit Final Temp.
c. 20 18 23 22 29 26 37 36
Copper Deposited Electrolytic Electrolytic gravimetric colorimetric
%’
7;
0.12 0.12 0.12 0.12 0.13 0.13 0.14 0.14
0.12 0.11 0.11 0.12 0.12 0.12 0.13 0.12
Color of Deposit Bright red Red Red Bright red Red Red Reddish black Reddish black
Drops of iiitric acid can also be used to oxidize the copper. The ferrous ion is oxidized t o ferric ion which in turn oxidizes the copper. It is important to keep the temperature low. When theinitial temperature of the solution is high, the deposit will be black in color and the result high. Table I1 illustrates the effect of temperature on the deposition of copper from a commercial steel containing 0.12% copper. These results indicate that initial temperatures of 7”, 12”, and 18” C. will give good results. Ice was required to attain temperatures of 7 ” and 12’ C. Since the results obtained at these temperatures were no better than those obtained at 18” C., the solutions were all cooled to 18” C., easily reached by partly immersing the beakers in running tap water about 0.5 hour. Voltages from 2.0 to 2.6 were studied. All other factors being , the same, the copper deposits become darker in color i~ the voltage is increased and a t 2.6 volts are black. However, the accuracy of the method is not appreciably altered. The voltage employed does not change to any appreciable extent the time required for electrolysis. With voltages 2.0 and below, the copper does not plate out or does so very slowly. Hence, the importance of maintaining a voltage of 2.1 to 2.2 is obvious. About 40 to 45 minutes are required to plate the copper from an ordinary carbon steel whose copper content is 0.370 or less. When the copper content is higher than 0.3%, a correspondingly longer time is required. Ordinarily, the deposition will be noticeable in from 1 to 5 minutes, but if too large an excess of ferric ion is present at the start, it will take longer. For plain carbon steels and cast irons, the deposit will usually be a darkish red color. Some deposits will be bright red in color while others almost black. However, regardless of color, the results will be satisfactory. Copper deposits from alloy cast irons and molybdenum steels will usually be a dull black. Those from samples containing much tungsten or chromium will be black with a bluish tinge. The principal sources of error in thib method are incomplete oxidation of the copper by the ferric sulfate treatment, diffusion of the copper ions into the anolyte, absorption of copper ions by the Alundum cell, and copper remaining in the catholyte. These sources of error were investigated and in only a few instances was NE much as 0.1 mg. of copper found in any one source. LITERATURE CITED
Yoc. for Testing Materials, “Methods of Chemical Analysis of Metals”, p. 28, Philadelphia, 1939. Brediani, H. A,, and Hale, C. H., IND. ENG.CHEM.,ANAL.ED., 12, 736 (1940). Glasstone, S.,and Hickling, A,, “Electrolytic Oxidation and Reduction”, p. 128, New York, D.Van Nostrand Co., 1936. Lundell, G. E. F., Hoffman, J. I., and Bright, H. A., “Chemical Analysis of Iron and Steel”, p. 265, New York, John Wiley 8: Sons, 1931. Mehlig, J. P., IND.ENQ.CHEM., ANAL.ED., 13, 533 (1941). Mellan, I., “Organio Reagents in Inorganic Analysis“, p. 366, Philadelphia, Blakiston Co., 1941. Sand, H. J. S., “Gravimetric Electrolytic Analysis”, Vol. 2, p. 117, London, Blackie and Sons, 1940. Silverman, L.,Goodman, W., and Walter, D., IND.ENQ.CHEM., A N ~ I , ED., . 14,236 (1942).
(1) Am.
(2) (3) (4)
(6) (6)
(7) (8)
