Mar., 1915
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
DETERMINATION OF COPPER IN STEEL‘
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( I ) 4CuCNS 7KI03 14HCl = 4CuSOa 7ICl 4HCN 7KCl jHzO, from which i t is I n view of t h e increased use of copper in steel as a seen t h a t 7KIO3 oxidize 4Cu and a n iodate solution preventive of corrosion and of t h e necessity of com- made accordingly gave correct results on titration pleting t h e determination in a very short time, a rapid using chloroform. If now t h e solution be diluted a n d a n d accurate method for t h e determination of copper a n excess of potassium iodide be added t h e iodine in steel is essential t o a steel works laboratory. chloride (IC1) will be changed t o free iodine according t o t h e reaction: The precipitation of copper by potassium or am7KCl; 7KI03 oxidize 4Cu ( 2 ) 7ICl 7KI = 141 monium thiocyanate solution has been used in t h e gravimetric determination of copper. Van Name2 a n d a t t h e same time liberate 141, or IKIO, liberates has shown t h a t , under certain conditions of concen- 2 1 . The excess of KIO3 has been reduced b y potastration, acidity, etc., t h e precipitation is complete. sium iodide according t o t h e reaction: jKI 6HC1 = 6KC1 3Hz0 61, (3) K I 0 3 Treadwell and Hall3 describe a method for t h e titration of cuprous thiocyanate (CuCNS) with potassium from which i t follows t h a t one KIOI in excess liberates iodate; in this titration iodine is a t first set free a n d 61 whereas each K I 0 3 which oxidizes copper liberates absorbed by t h e chloroform added as a n indicator, Z I or l / 3 t h e former. Therefore of t h e oxidizing power of potassium then oxidized b y more iodate t o iodine chloride, t h e iodate is reclaimed on addition of potassium iodide. violet color disappearing from t h e chloroform. I n t h e method submitted here potassium iodate It was shown t h a t 4Cu = 7KIOa in concentrated is used in excess a n d t h e excess, after t h e addition of acid solution ( I ) . I n dilute solution, after addition potassium iodide, is titrated with sodium thiosulfate. of potassium iodide, 4Cu = ”3 of 7KI03 or ICU = ‘/e KIO3. METHOD-Five grams of steel are dissolved in 65 For the above titration I cc. should equal 0. I per cc. of a mixture of 40 cc. nitric acid ( 1 . 2 0 sp. gr.) cent copper on a 5 g. sample or I cc. = 0.005 g. copand 2 5 cc. sulfuric acid ( I : I ) a n d t h e solution evapper. Then I cc. should contain 0 . 0 0 5 X 7KI03/6Cu orated t o fumes of sulfur trioxide in a covered poror 1000 cc. should contain 19.64 g. potassium iodate. celain dish over a high flame; care must be taken t h a t A solution of potassium iodate was standardized with all nitric acid is expelled. The dish is removed from sodium thiosulfate against potassium permanganate t h e heat and, when cold, 5 0 cc. of hot water are added which had been standardized against sodium oxalate a n d t h e solution boiled, transferred t o a No. 5 beaker a n d i t was found t h a t t h e “ C . P.” salt contained b u t and diluted t o 400 cc. with hot water. When all 97 per cent of its theoretical oxidizing power, there t h e ferric sulfate is in solution, 50 cc. strong ammonium being some potassium carbonate present as well as bisulfite are added, while stirring, followed by 2 5 other impurities. Taking this into consideration t h e cc. of 5 per cent potassium thiocyanate. The solusolution of potassium iodate is made b y dissolving tion is boiled until precipitation is complete, which 2 0 . 2 g. salt a n d diluting t o I liter. The solution of sorequires five minutes, and filtered by suction through dium thiosulfate is made by dissolving 137 g. per liter a 11 cm. No. o Munktell filter, t h e precipitate and is made t o agree with t h e iodate solution if necesa n d breaker being washed with cold I per cent sary. These solutions are best standardized against sulfuric acid solution. Paper a n d precipitates are permanganate in t h e well known way. transferred t o a beaker, 2 0 cc. hydrochloric acid ( I : I) REsuLTs-On determining copper on a solution of are added, followed by standard potassium iodate copper sulfate containing t h e equivalent of 0 . 2 5 per solution (2 cc. for each 0 .I per cent copper expected). cent copper, good results were obtained. The paper is well macerated with a glass rod and water added t o a volume of 500 cc.; t h e potassium RESULTSON A COPPER-STEEL STANDARD iodide solution is now added ( I cc. of I O per cent solu- LaboraI’er cent LaboraPer cent tory Method cu tory Method cu tion for each cc. of iodate added) and free iodine ti1 Not given.. ..... 0.216 8 Not given.. ............ 0 . 2 1 2 ~ o t g i v e ....... n .. 0.21 9 Not given .............. 0 . 2 0 6 trated with standard thiosulfate solution; t h e thiosul3 Not given.. ..... .. 0.21 Not given.. ............ 0.214 4 Not given ....... . . 0 . 2 2 2 10 Not given ............... 0.21 fate should be added rather slowly a n d t h e solution Electrolysis.. .... .. 0.224 Duquesne grav. CuO .... 0 . 2 15 stirred vigorously, care being taken t h a t no p a r t of t h e Duquesne vol. KIOs, . 56 Vol. and elec.. .. ... 0,205 0.21 NaaCzOa s t d . . ........ 0.213 Electrolysis. ..... solution is bleached before t h e whole. When t h e 7 Electrolysis.. .... 0.204 AVERAGE. ........... 0 . 2 12 yellow color of free iodine has nearly vanished, 5 cc. starch solution are added a n d t h e titration continued Results by Steel Works Laboratories on a copper until t h e blue is bleached. The difference between steel standard were as given above. t h e iodate a n d thiosulfate represents t h e copper. DUQWESNE WORES.CARNEGIE STEELCo. DUQUESNE, PA CALcuLATIoNS-The reactions a n d calculations are rather intricate. The iodate when in excess oxidizes the copper thiocyanate as follows (Treadwell a n d RECOVERY OF MOLYBDIC ACID’ Hall) : By W. D . BROWN By W. D. BROWN
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1 Presented before the Pittsburg Section of the American Chemical Society, January 21, 1915. 2 A m . J. Sci., 10, 451; la, 20, and Gooch’s “Chemical Analysis,’: p 108. 8 “Analytical Chemistry.” Vol. I1 (1914), p. 672; ( l Q l O ) , p. 599. See also J. A . C. S., SO (1908), 760.
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On account of t h e rise in price of molybdic acid, a n a t t e m p t was made in t h e Duquesne Laboratory last 1 Presented before the Pittsburg Section of the American Chemical Society, on January 21, 1915
