INDUSTRIAL AND ENGINEERING CHEMISTRY
November, 1927
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1285
Determination of Slag and Oxides in Wrought Iron' By Blaine B. Wescott,2 Frederick E. Eckert,3 a n d Harry E. Einert4 ?vlELLOii
INSTITUTE OF IKDUSTRIAL RESEARCH, UNIVERSITY OF PITTSBURGH, PITTSBURGH, PA.
INCE the advent of steel the interest in and the use Bette16 treated the iron borings with bromine and potassium bromide ~ ~ solution i ~ toheffect - solution oT the iron, leaving the slag of wrought iron have steadily decreased. ~ ~ ~ undissolved. He also used copper potassium chloride to dissolve standing this trend in industry,' however. Tvrought the iron away from the slag. Barrows and Turner' passed chloiron today fills a definite need and supplies a certain demand rine over the iron drillings contained in a boat in a combustion of the trade because of the unusual properties that make it tube a t a high temperature. The iron was converted into ferric particularly clesirable for purposes. ~ ~ ~ chloride, ~ which ~ was sublimed ~ ~ and carried i away ~ from ~ the slag ~ remaining behind in the boat. They stated, however, that the Work upon wrought iron has not kept pace with research in method gave low results, because of the volatilization of some ferthe steel industry, and there is a consequent lack of accurate rous oxide, according to the following equations: information concerning many of its fundamental properties. 3Fe0 = Fez03 Fe Ordinary methods of analysis furnish but very little useful Fe + 3C1 = Fee13 information when applied to wrought iron, because they They also found that high results were obtained when the give no indication as to the amount of slag present and tell solution of the iron was nothing as to how the varieffected by sodium copper ous constituents are divided chloride. This observation between the base metal and was due to the oxidation of T h e need for research in the w r o u g h t i r o n i n d u s t r y some ferrous iron during the the included slag. is pointed out. Errors a r e s h o w n to exist i n m e t h o d s ignition of the slag residue. The characteristic propformerly used for the d e t e r m i n a t i o n of slag a n d oxides. They recommended that a erties possessed by wrought deduction of about 5 per cent A modified m e t h o d is described which n o t only is capabe made in order to correct iron find their origin in the ble of yielding m o r e accurate results t h a n f o r m e r the error. U'ilner and XIercks small amount of slag which methods, b u t m a y be a d a p t e d €or the d e t e r m i n a t i o n of determined the amounts of is mechanically entrained t h e distribution of silicon a n d m a n g a n e s e between metallic iron and iron oxides and evenly d i s t r i b u t e d in ferrum reductum by treatt h e base m e t a l a n d slag. T h e modified iodine m e t h o d ing the sample with mercuric throughout the body of the has been proved t o be rapid e n o u g h for r o u t i n e work chloride, while ChristensenD base metal, which is of a by a c t u a l experience a n d should f u r n i s h the s t a r t i n g made the same determinahigh degree of purity. The p o i n t for research u p o n the chemical a n d physical tions by using ferric chloride peculiar fibrous structure, as to dissolve the metallic iron. constitution of w r o u g h t iron a n d t h e i r relation to s u c h Slarquardt'o used iodine and well as the musually effecf u n d a m e n t a l properties as fatigue a n d corrosion potassium iodide for the same tive resistance to fatigue and resistance a n d also weldability. purpose. corrosion, is greatly, if not By far the best method, entirely, dependent upon the h o w e v e r , was the iodine method proposed by Eggertz, presence of included slag. For these reasons the determination of slag in wrought iron is as given:by Blair." Iodine was added gradually to a mixture of the sample and cold water in a beaker surrounded with important, and an accurate method for this determination is ice. The sample was stirred a t intervals for several hours unof course essential. Any method that effects :a mechanical til all the iron had dissolved. The mixture was then filtered, separation of base metal and slag, thereby permitting dis- and the slag residue washed with cold water and dilute hydrotinct analyses of each, is of value to the industry because of chloric acid until the washings gave no test for iron: The residue, consisting of slag, iron oxide, graphite, carbothe information which may thus be obtained concerning slag naceous matter, and some silica, was then boiled with potasthe influence of various elements upon weldability, corro- sium hydroxide solution to dissolve the silica. After filtering and sion resistance, and the other properties of wrought iron. washing with hot water and dilute hydrochloric acid, the residue Interest in wrought iron is especially intensified a t this time of slag and iron oxide was ignited and weighed. The most recent research reported in the literature was that of because of recent developments in manufacturing practice Wust and N. Kirpach.l* These investigators based their work by mechanical means which seem destined not only to give upon that of Schneider,*3who classed the available methods into a product of satisfactory quality but to effect such savings two groups. The first group included the chlorination method, in manufacturing costs that the field of usefulness for wrought- in which there was a loss due to the reaction between carbon and oxide inclusions, and also those methods employing acids to iron products will ultimately be broadened. accelerate the solution. The second group embraced the many
S
+
Historical Review Snelus6 first attempted a separation of metal from slag by pounding up the sample in a steel mortar. The slag, being brittle, was powdered, while the iron was flattened out. The resulting mixture was separated by a sieve or magnet, and the slag was then weighed and analyzed. He later used the titanium content of the sample to calculate the percentage of slag. Since samples of molten iron from the furnace did not contain any titanium, he assumed that all the titanium was contained in the occluded slag, and that therefore, by analyzing for titanium in the slag and metal, he could calculate the percentage of slag.
methods by which a separation was effected without destroying the structure of the slag. Wust and Kirpach studied only the methods of the second group, which included iodine, bromine, and salts of mercury and copper. After consideration, the study of the salts of mercury and copper was omitted, and the research limited to iodine and bromine. The bromine method afforded the most rapid means of dissolving the steel and was adopted by them. The slag and oxide residue after solution of the iron was washed with ammonium tartrate and oxalic acid. Upon using this method for the determination of slag in a sample of wrought iron, these investigators found that it took twenty Chcm. News, 43, lOb(1881). J . Chem. SOC.(London), 61, 551 (1892). 8 Farm. Tidskvifl, 1880, 225; Z . anal. Chem., 41, 710 (1902). 8 Ibtd., 44, 535 (1905). 10 Chem.-Zfg.,46, 743 (1901). 11 "The Chemical Analysis of Iron," p. 78. * a Kaiser Wilhelm I n s t i f u f f i i rEisenforschung, 1, 31 (1920). 1: Oesfcw. 2. Berg- Hiiftenw., 48, 257, 275 (1900). 6
7
I 2
Received May 23, 1927. Industrial fellow, Mellon Institute of Industrial Research Pittsburgh,
Pa. 6 4
3
Chief chemist, A. M. Byers Co., Pittsburgh, Pa. Chief chemist, Cyrus W. Rice Co.,Pittsburgh, Pa. 3. Iron Sled Inst. (London), 1, 258 (1872).
i
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INDUSTRIAL A N D ENGI,VEERING CHEMISTRY
washings with oxalic acid to give a residue of slag of constant weight. They therefore substituted a washing solution of 5 per cent sulfuric acid containing some potassium dichromate. Only three washings were necessary to give a constant weight with this solution. The following method was finally adopted: 200 cc. of a solution of 200 grams bromine and 400 grams potassium bromide in 1000 cc. water were added t o a 500-cc. Erledleyer flask. The solution was heated to 80" C. on a water bafh and 5 grams of billings were added. The flask was agitated from time to time. After 4 hours the solution was filtered and the residue washed with 5 per cent sulfuric acid, t o which had been added some potassium dichromate. The residue was ignited and weighed. They concluded that iron carbide, phosphide, and sulfide, and manganese sulfide were easily dissolved, silicon and manganese in ordinary amounts were dissolved, and nickel was partly oxidized. In the presence of carbon errors were introduced in the determination of silicon, manganese, and chromium, and likewise in the case of iron nitride. They believed that the method was not entirely satisfactory in all cases.
Experimental
Vol. 19,No. 11
One-half gram of the t a p cinder was stirred for 1 hour with a solution of iodine dissolved in iron iodide. The cinder was then filtered off by suction and washed free of iron and iodine with boiling hot water. The suction was disconnected and the funnel filled t o the top of the paper with boiling hot 10 per cent potassium hydroxide solution, which was allowed t o run through the filter by gravity. When all the caustic had passed through the filter, the flask was again connected to the suction and the paper washed with boiling hot water until the washings did not react alkaline to phenolphthalein. The paper and residue were then ignited and weighed.
As a result of ten such determinations it was found that the average change in weight of the tap cinder was a gain of 3.66 per cent. Upon ignition alone, the tap cinder gained 7.0 per cent in weight in consequence of the oxidation of ferrous oxide. Consequently, a slight loss resulted from the treatment with iodine and caustic, which was probably due t o the presence of a small amount of metallic iron in the tap cinder. The theoretical amount of slag in the mixtures calculated from these data was 3.50 per cent. Table I contains the results of several analyses of the prepared samples, some of which were washed with 1:20 hydrochloric acid (Eggertz method) and the others treated according to the modified method outlined above.
Some of these methods were studied for the purpose of obtaining a rapid and accurate procedure for use in routine control laboratories. The four most promising methods were the chlorine combustion method, solution of the iron in cupric potassium chloride, the iodine method, and the Samples by Eggertz and Modified bromine method. Only the last two were studied, however, Table I-Slag Content of Prepared Iodine Methods EGCERTZ MODIFIED CALCD. SLAG since it had been previously shown by one of the writers SAMPLE METHOD METHOD A N D OXIDES that the chlorine combustion method gave low and varying Per cent Per cent Per cent results when used for the determination of slag, and had de1 2.47 3.39 2 2 . 5 3 3 . 4 3 cidedly doubtful value for the determination of the distribu3 2.50 3.36 3.50 4 3.32 tion of phosphorus and silicon between base metal and slag. 5 2.76" 3.26 The bromine method also gave low and inconstant results 3.26 6 Average 2 50 3 34 3 50 when used in water solution, with potassium bromide and a Only washed twice with acid, not included in average. with organic solvents such as alcohol and acetone. The copper potassium chloride method gave high results because The results show clearly the error introduced in the deof hydrolysis of iron salts during the solution of the sample. The iodine m t h o d of Eggertz possessed certain objection- termination by washing the slag and oxide residue with l :20 able features. one of which, in particular, led to inaccurate hydrochloric acid. Even by omitting the acid wash the tendresults. The amount of time required to effect the solution ency in these analyses was towards low rather than high of the sample was a serious drawback, especially for use as results, possibly owing t o the presence of small amounts of a routine method in control laboratories. This objection did metallic iron in the tap cinder. Indeed, the occurrence of not prove serious, however, since it was found unnecessary, metallic iron in tap cinder is very common. DETERMINATIONS ON WROUGHT-IRON SKELP-Similar dein the first place, t o add the iodine gradually and, in the second, to keep the solution cold while the iron dissolved. To the terminations were carried out on a sample of wrought-iron contrary, the rate of solution was materially increased by skelp, with similar results. The effect of acid washing upon using warm water and the time required for solution of the the slag recovered from wrought iron was, if anything, more iron was further shortened by continuously stirring the mix- marked than in the case of the prepared sample. Samples ture with a mechanical stirrer. K i t h these modifications of recovered slag, which were dried after the treatment with the time required for solution of the iron was reduced from caustic for the removal of the base metal silicon remaining about 7 hours to 1 hour or less without sacrifice of accuracy. behind with the slag, gained about 1 per cent in weight The principal objection to the method of Eggertz, however, upon ignition, while samples of slags dried without caustic was the use of dilute hydrochloric acid for washing the residue treatment lost from 4 t o 8 per cent, varying with the different of slag and oxides. It was shown conclusively, by many samples of slag. The methods used were identical with those described for trials, that acid, even of the dilution recommended by Eggertz the prepared samples, Table I1 contains a few of the many (1:20), had a very considerable solvent action upon the slag. It was found necessary to dispense altogether with acid wash- results obtained by the three methods under varying coning because such a procedure inevitably led to low results. ditions, as referred t o therein. Boiling hot distilled water was therefore used throughout Table 11-Slag Content of Wrought Iron Skelp by Iodine Method MODIFIED IODINE METHOD for washing the slag and oxide residue. Treated Not treated DETERMINATIONS ON PREPARED MIXTURES-TO establish EGGERTZ with Not treated with KOH; SAMPLE METHOD KOH with KOH residue dried the accuracy of the modified method determinations were Per cent Per cent Per cent Per cent made upon prepared mixtures of plain low-carbon steel and 3.50 3.55 3.51 3.48 ordinary puddle furnace tap cinder, since no standard samples of wrought iron were obtainable. The mixtures consisted of 4.85 grams of the steel and 0.15 gram of the tap cinder. The steel itself contained 0.40 per cent of oxides by Average 2.67 3.52 3.48 3.63 the modified iodine method, so that the apparent slag content Here again there was a wide difference between the results of the samples became 3.39 per cent. The variation in weight of the tap cinder during the course of the analysis was de- obtained by the Eggertz and the modified methods. It is only necessary to collect the acid washings in a clean disk termined as follows:
ILVDUSTRI.4L A N D ENGINEERING CHEMISTRY
November, 1927
and render them alkaline in order to detect the error introduced by the use of the acid wash recommended by Eggertz. EFFECTO F OMITTING ALKALI TREATMENT-However, another factor was overlooked in the old method which exerted just as great an influence upon the correctness of the results. The treatment of the slag and oxide residues with alkali may cause low results because of its solvent action on slag phosphorus. The magnitude of the error may range from a difference within the limits of experimental error to more than 0.5 per cent, depending upon the amount of phosphorus in the slag. Alkali that was too weak to dissolve freshly precipitated silica effectively still exerted a strongly solvent action on slag phosphorus. A sample of tap cinder containing 1.72 per cent phosphorus was found to have retained but 0.98 per cent phosphorus after treatment with 10 per cent sodium hydroxide. This point is well illustrated by the analyses in Table 111, made on a sample of ordinary hand-puddled wrought iron skelp containing 0.267 per cent phosphorus and 0.157 per cent silicon. TableJII-Effect of Caustic Wash on Determination of Slag i n HighPhosphorus Wrought Iron by Modified Iodine Method NUMBER
1 2 3 4 5 Average
WITH CAUSTIC WASH
Per cent 2.16 2.09 2.16 2.06 2.06 2.11
WITHOUT C A U S T I C WASH
Per cent 2.98 3.00 2.82 2.97 2.92 2.94
On the other hand, errors just as serious may 138 introduced by omission of the treatment of the slag and oxide residue with alkali, because of the oxidat.ion of appreciable amounts of base metal or silicide silicon during the solution of the .ample in iodine. The analyses in Table IV illustrate such an instance. The sample in question was taken from a piece of mechanically puddled wrought iron skelp containing 0.122 per cent phosphorus and 0.517 per cent silicon. The slag and oxide residues were analyzed for silica in the usual manner. Table IV-Effect of Caustic Wash on Determination of Slag i n HighSilicon Wrought Iron by Modified Iodine Method WITHCAUSTIC WASH WITHOUTCAUSTIC WASH SUMBER Slag Silica in slag Slag Silica in slag Per cent Per cent Per cent Per cent 1 3.24 23.48 3.98 28.27 2 3.28 23.65 3.95 28.17 3 3.24 23.87 3.94 27.92 Average 3.25 23.67 3.94 28.12
The accuracy of the determination of slag and oxides may not be materially affected, however, on samples containing relatively small amounts of both phosphorus and silicon. A very great proportion of the wrought iron made today falls within this classification. A smaller proportion contains higher percentages of phosphorus, and seldom, if ever, will the present product be found to contain large amounts of bot,h silicon and phosphorus. The analyses in 'Table V were made upon a sample of hand-puddled wrought iron pipe containing 0.105 per cent phosphorus and 0.136 per cent silicon. Table V-Effect of Caustic Wash o n Determination of Slag i n LowPhosphorus, Low-Silicon Wrought Iron by Modified Iodine Method WITHCAUSTIC WASH WITHOUT CAUSTIC WASH Slag Silica in slag Slag Silica in slag NUMBER Per cent Per cent Per cenl Per cent 1 2.92 8.26 2.97 9.88 2 2.97 8.43 2.93 9.66 3 2.93 8.54 2.99 9.71 Average 2.94 8.41 2 96 9.75
These results show that, although no appreciable error was introduced in the determination of slag and oxides by omitting the treatment with alkali, there was a difference in the amounts of silica found in the residues. A study of the tables makes it evident that the method used for the determination of slag and oxides in wrought
1287
iron must be varied in certain details to conform with the phosphorus and silicon contents of the individual samples. While it is manifestly impossible to establish definite limits of the two elements which would determine the treatment to be used, the following general statements may be made: I-When the total phosphorus content is 0.150 per cent or less, the caustic wash may be used without causing more than a very small error. 2-When the total phosphorus content is more than 0.150 per cent, the use of the caustic wash will give low results. 3-When the total silicon content is 0.150 per cent or more, omission of the caustic wash will give high results. 4-Accurate determinations of the distribution of silicon between base metal and slag are impossible unless the caustic wash is used. 5-When both DhosDhorus and silicon are hiah. the amount of slag must be calcdated from determinations made both with and without caustic treatment.
ANALYSIS OF SLAG-Considerable attention has been given in this work to the ultimate analysis of wrought iron or to the determination of the distribution of the various elements between the base metal and inciuded slag. The residue of slag and oxides obtained from the iodine method may be analyzed for silica, manganese, and iron by the usual methods for ore analysis. Manganese in the slag may be determined in the filtrate from the determination of silica in the slag. If determinations of total ferrous or ferric iron in the slag are desired, it becomes necessary to treat 30 grams or more of the sample with iodine. The residue should be dried, but not ignited, ground in an agate mortar, and passed through a 200-mesh sieve. The distribution of sulfur may be readily found from determinations of total sulfur by the oxidation method and base metal or sulfide sulfur by the evolution method, the difference between them being sulfate or slag sulfur. Distribution of phosphorus cannot be determined by analysis of slag residues and this procedure will form the subject of another article. Procedure
The details of the modified iodine method as adopted for the determination of slag and oxides were as follows: SLAGAXD OxIDEs--Weigh out 3 grams of the drillings of the wrought-iron sample into a 100-cc. beaker and add 20 grams of resublimed iodine. Then add 30 cc. of distilled water t o the mixture in the beaker. After the first violent reaction has subsided, wash down the sides of the beaker with a small quantity of distilled water, place the beaker in a stirring machine, and stir vigorously for 1 to 2 hours. At the end of that time rinse off the stirrer into the beaker and filter the mixture by suction through a 9- or 11-cm. filter paper. Wash the filter with boiling hot distilled water until no trace of iodine remains on the paper and no test for iron is obtained in the washings. Disconnect the filter flask from the source of the suction and fill the funnel to the top of the filter paper with boiling hot 10 per cent potassium hydroxide solution. Allow the caustic t o pass through the filter paper by gravity and then repeat the treatment with oaustic once more in the same manner. When all the potassium hydroxide has run through the filter, connect the filter flask to the suction again and Fvash the filter paper with boiling hot distilled water until the washings do not react alkaline to phenolphthalein. Dry the filter paper and residue, ignite, and weigh as slag and iron oxide. Retain the ignited residue for the determination of silica and manganese oxide in the slag. The reaction between the iron and iodine is very violent a t first and it is sometimes necessary t o cool the mixture either by the addition of small amounts of cold distilled water or by setting the beaker in cold water to prevent its boiling over the top. After the first reaction has subsided, most of the iron is in solution and there is no further danger of boiling over.
INDUSTRIAL AND ENGINEERING CHEiMlXTRY
1288
A very strong filter paper is necessary to withstand the treatment with boiling hot 10 per cent potassium hydroxide solution. The treatment of the slag and oxide residue with caustic should be regulated, of course, by the conditions mentioned earlier in this paper. SILICAIN SLaG-Treat the ignited residue of slag and oxides obtained from the modified iodine method with about 25 cc. of 2:l hydrochloric acid in a 100-cc. beaker. Evaporate the solution just to dryness and add 5 to 10 cc. of concentrated sulfuric acid. Heat for 15 minutes t o heavy fumes of sulfuric acid, cool, dilute to 40 cc., and add 10 cc. of concentrated nitric acid. Boil until all salts are in solution, filter, and wash the paper and residue free of iron with hot dilute nitric acid and hot water. Keep the filtrate for the determination of manganese. Wash the paper free of acid with hot water, catching the washings in a different receiver. Dry the paper and residue, ignite, and rreigh. Moisten the
Vol. 19, No. 11
ignited residue with a few drops of concentrated sulfuric acid and then add 10 cc. of hydrofluoric acid. Evaporate carefully to dryness, then ignite and weigh the residue. The difference in the two weights is the weight of silica in the slag. The percentage of silicon in the slag, calculated from this determination, subtracted from the percentage of total silicon gives the percentage of silicon in the base metal. ~IAXGASESE IN SLAG-COO~ the filtrate from the silica determination to 15" C., add a slight excess of sodium bismuthate (about 0.5 gram), and agitate for about a minute. Filter by suction through an asbestos pad, washing the flask and pad with 3 per cent dilute nitric acid, making sure that the last washings are colorless. Titrate immediately with a standard solution of sodium arsenite to the disappearance of the pink color. From this titration the percentage of manganese in the slag may be calculated and the figure thus obtained is subtracted from the total manganese to get the amount of manganese in the base metal.
Estimation of Copper Oxide and Metallic Copper in Mixtures Containing Both' By W. D. Bonner and Bal Dev Kaura UNIVERSITY OB U T A H , S A L T
DIRECT method for the quantitative determination of cuprous oxide and copper in a sample containing both has not been known, although one can determine cuprous oxide indirectly by reducing with hydrogen and finding the amount of water formed. The work here reported gives a simple and fairly accurate method for determining these two when both are present. It may be especially useful in the cement copper industry, where, owing both to oxidation during drying and to direct precipitation as cuprous oxide, the cement copper always contains oxide and it is often desirable to know the amount.
A
Experimental
'
RATE OF SoLuTIow-This method is based on the fact that copper dissolves much more slowly in an alkali cyanide solution than does cuprous oxide. It has long been known that metallic copper dissolves in an alkali cyanide solution with the evolution of hydrogen, but neither the rate of solution nor the extent to which copper is soluble has been determined. Therefore the rate of solution of copper in molar sodium cyanide solution was first determined. It was found that copper free from oxygen dissolved only to the extent of about 0.2 gram per liter of cyanide solution in 3 hours, when allowed to stand a t room temperature with an occasional shaking. I n the same length of time molar sodium cyanide solution would dissolve enough cuprous oxide from an excess of the solid to form a saturated solution-i. e., about 30 grams per liter-while cupric oxide, exposing the same surface area as the metallic copper, would dissolve to the extent of 3.5 grams per liter. Pure copper was prepared by passing hydrogen over heated cupric oxide wires One portion of this copper was kept under hydrogen, another under nitrogen, and a third was exposed to air. Equal weights (5.325 grams) of these different samples of copper with 150 cc. of 1.04 M sodium cyanide solution were placed in 250-cc. Erlenmeyer flasks and stoppered with rubber stoppers each having a long glass tube to let out the gas evolved. They were then placed in the 1 Received
June 14, 1927.
LAKECITY,
UTAH
thermostat a t 25" C. and samples of the solution taken a t intervals to be analyzed for copper content. Table I-Rate of Solution of Copper in Molar Sodium Cyanide COPPER SAMPLE 3 5 9 12 24 5 HOURS HOURS HOURS HOURS HOURS DAYS I n hydrogen 0.20 0.26 0.70 0.85 3.00 9.87 I n nitrogen 0.20 0.30 0.75 0.99 3.25 11.00 I n air 0.40 1.10 1.75 5.50 12.70 0.66
The results (Table I) show a wide difference in the initial rate of solution of the different coppers. Copper exposed to air dissolves about twice as fast initially as that kept under hydrogen or nitrogen, but the rates become more and more uniform with lapse of time. The copper kept under nitrogen dissolves a little faster than that kept under hydrogen, probably because the nitrogen, having been prepared from liquid air, contained some oxygen. The reaction between (Ch-)- and copper may be written as suggested by Kunschert :2
+ 4(CN)- + HzO C U ( C N ) ~ - - -+ (OH)- + CU~O + 8(CN)- + HzO = 2Cu(CN)* ---+ 2(OH)-
CU
'/2H2
That between Cu!O and (CN)- may be written similarly: The greater reaction rate of the cuprous oxide (or of the copper exposed to air) is therefore probably due to its greater solubility in water. Table 11-Seuaration
NO.OF
DETNS. Mean Deviation
__
of Couuer f r o m Cuurous Oxide
COPPERI N RESIDUE Mg. 249.95 4-0.04 to -0.09
CunO I N FILTRATC Mg. 250.01 t O . 1 9 t o -0.06
CORIPLETEXESS OF SEPARATION OF CUPROUS OXIDE FROM COPPER-Pure cuprous oxide was prepared by reducing Fehling's solution with sugar. This cuprous oxide readily dissolves in sodium cyanide solution. A mixture of pure copper and pure cuprous oxide (250 mg. of each) was added to 50 cc. of 0.5 M sodium cyanide solution and the whole allowed to stand for about 2 hours with occasional shaking. It was then filtered and copper determined, by the iodide method, in both residue and filtrate. 9
2. anorg. Chcm., 41, 359 (1904).
