I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
58
Vol. 16. No. 1
T h e Determination of Manganese’ Part I-A Study of the Bismuthate Method By T. R. Cunningham and R. W. Coltman THBUNIONCARBIDE & CARBON RESEARCH LABORATORIES, INC., LONGISLAND CITY,N. Y.
ard, and, in the absence HE bismuthate In this paper the application of the bismuthate method fo the demethod for the deterof a better compound, retermination of large quantities of manganese is described in detail. sorted to anhydrous manmination of mangaZ t is shown that by proper regulation of the acidity and oolume of ganous sulfate, a salt that nese in iron and steel is the solution, weightsof manganese as highas 500 mg. can be accurately can be obtained of theoretgenerally conceded to be determined. A description is giuen of experiments relatiue to the ical composition only by the most accurate analytioxidizing power of sodium bismuthate and the stability of solutions adherence to certain rather cal procedure for the deterof permanganic acid under trarying conditions of acidity and conspecial conditions. In manmination of this metal. In centration. Analytical procedures for the determination of mangaganous oxalate, however, a addition, it is simple and nese in manganese ores, ferromanganese, and manganese metal salt has been found that rapid, as usually no previare outlined. possesses all the properties ous separation of the manPart ZI, which is reserued for future publication, will describe necessary for a primary ganese from iron or the the preparation of pure manganous oxalate, its use as a primary standard. The results of other metals found in steel standard in connection with the determination of manganese by a study of the properties of is necessary. The process Volhard’s method; the chlorate method and similar processes will be this compound and of its is based upon the fact that proposed. use as a standard salt will under certain conditions be given in Part 11. bivalent manganese can be The bismuthate method was originally proposed by Schneicompletely oxidized to permanganic acid by sodium bismuthate, the corresponding amount of permanganic acid formed der14 who used bismuth tetroxide as the oxidizing agent, titrating the permanganic acid with hydrogen peroxide. being then determined volumetrically. The application of the bismuthate method has been largely Reddrop and Ramage6 modified Schneider’s procedure by confined to iron and steel or other materials containing using sodium bismuthate, which can be more readily obrelatively small amounts of manganese. Most of the workers tained free from chlorine. The method in its present form state that the oxidation of the manganese is complete only is due to Ibbotson and Brearley16who replaced the hydrogen when the weight present does not exceed 50 mg. For exam- peroxide by ferrous ammonium sulfate, a salt which is more ple, in describing the determination of manganese in manga- stable than hydrogen peroxide and does not react with ferric nese ores, Blair2 calculates the manganese present on only 20 nitrate as does the latter. The most recent and complete mg. of ore, while Blum3 states that 50 mg. of manganese is investigation of the method, to which reference has already about the limit that can be handled with accuracy. It is been made, is that of Blum. Other workers in this field are obvious that in the former case small errors in measurement referred to in the bibliography at the end of Part 11. introduce enormous percentage differences, and in the analysis The conditions under which the method must be carried of such a product as manganese metal, a substantially pure out are so familiar that no outline will be made of them here; product, even 50 mg. is much too small a quantity upon which they will be taken up in detail later, when the various facto base an accurate percentage calculation. This limitation tors are discussed. There are but few references that bear in the weight of manganese that could be used for a determi- upon the present problem, the determination of relatively nation has prevented the general adoption of the method by large quant,ities of manganese, as most writers have limited industrial laboratories engaged in the analysis of high-grade their descriptions of the process to materials containing manganese ores, high and low-carbon ferromanganese, and small percentages of the element. It is interesting to note, manganese metal. In looking over the data contained in however, that Schneider, who first proposed the method, Blum’s excellent paper, the authors noticed that 50 per cent used 0.0794 and 0.1587 gram of manganese in his test analyses. of the determinations made on aliquots containing 100 mg. Ibbotson and Brearly placed no limit on the amount of mangaof manganese yielded correct results. Believing it impossi- nese that could be present, but the conditions specified by ble that this could be the result of chance, they decided to them are not adapted to the accurate determination of large make a thorough study of the method with the object of weights of manganese. Blum definitely limits the amount to adapting it to the determination of much larger weights of a maximum of 0.05 gram of manganese. manganese than has heretofore been considered possible. I n working out the present improved procedure, the folAs will be shown hereinafter, the authors’ work has demon- lowing points were studied: (1) the oxidizing power of sodium strated that the limitations ascribed to the bismuthate method bismuthate, (2) the stability of the permanganic acid formed, can be overcome, and that the determination of manganese (3) the uniformity of oxidation of varying amounts of mangain quantities up to 500 mg. can readily be accomplished. nese, and (4) the correlation of the value of the permanganate While the foregoing considerations were in themselves used for titration with an absolute standard. sufficient to warrant a further investigation of the bismuthate So far as the writers have been able to ascertain, the first method, the existing status of still another important phase two points have not been studied in detail and the third has of the subject was felt to be unsatisfactory. Blum pointed never been carried to sufficiently high limits. The work on out in his paper that the development of exact methods for the the permanganate value in terms of manganese is merely determination of manganese had been greatly retarded by confirmatory of Blum’s work. the lack of a manganese compound suitable for use as a stand-
T
1 Received
July 12, 1923.
* “Chemical Analysis of Iron,” 8
4
1918, p. 119.
J A m . Chem Soc., 54, 1379 (1912).
6 0
Dinglers pobfech. J . , 269, 224 (1888). J . Chem. Soc., 67, 268 (1895). Chem. News, 84, 247 (1901).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
January, 1924
OXIDIZING POWER OF SODIUMBISMUTHATE In applying the bismuthate method to the determination of large quantities of manganese, it becomes necessary to have data on the exact oxidizing power of sodium bismuthate. Previously published outlines of the method as applied to steel have given rather indefinite directions regarding the amount of bismuthate to be used, it being stipulated, for example, that “an excess,” or “from 0.5 to 1 gram” should be employed. Although this latter quantity is ample for the weight of manganese present in the usual sample of steel taken (1 gram), it is obvious that when working with quantities of manganese as great as 0.5 gram: more exact information concerning this point is necessary. In order to determine the amount of bismuthate required to oxidize a definite quantity of manganese, a sample of bismuthate was used that, according to the results of an iodometric determination, contained 79.4 per cent sodium bismuthatc. Fifty-cubic centimeter aliquot portions of a solution of manganous nitrate containing about 1 mg. of manganese per cubic centimeter were placed in small flasks, and varying quantities of bismuthate were added to each. The solution contained nitric acid in the concentration usually recommended (specific gravity 1.135). After the bismuthate had been introduced the flasks were shaken for 1 minute and the solutions diluted with 50-cc. portions of water and filtered through asbestos. The permanganic acid formed was determined in the usual manner by adding a known amount of ferrous salt in excess and titrating the excess with 0.1 N potassium permanganate. TABLE I-OXIDIZING POWEROB SODIUM BISMUTAATE Bismurhate Grains
Manganese Found Gram
0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 2.0
0,0058 0.0164 0.0278 0.0374 0.0446 0.0486 0,0492 0.0493 0.0493
Manganese Oxidized by 1 Gram Bismuthate Gram
0.058 0.055 0.056 0.053 0.050 0.044 0.038
..... .....
Theoretically, from the relation 2 Mn : 5 NaBiOs, I gram of 100 per cent sodium bismuthate oxidizes 0.0785 gram of manganese, and a product containing 79.4 per cent sodium bismuthate should oxidize 0.0623 gram of manganese per gram. The maximum amount actually found was 0.058 gram, but in the presence of increasing weights of permanganic acid (from the oxidized manganese) the oxidizing power falls off because of the reversibility of the reaction. A’concentration of 0.0493 gram of manganese in 50 cc. corresponds to a normality of about 0.09; to oxidize manganese to this concentration about 26 grams (1.000/0.038) of 80 per cent bismuthate are necessary for 1 gram of manganese. These experiments show that the amount of bismuthate necessary depends upon the concentration of the permanganic acid formed. The usual procedure is to oxidize the manganese in the presence of nitric acid of specific gravity 1.135 and dilute the solution with an equal volume of water before filtering. Experiments described later show that after this dilution the optimurr, concentration of permanganic acid as regards stability in 1,henitric acid is about 0.05 N . This means that the permanganic acid should be present before dilution in a strength of about 0.1 N (0.0011 gram per cubic centimeter), and the data show that in oxidizing a manganese solution so that the resulting permanganic acid is 0.1 N , 1.3 gram of 80 per cent bismuthate are necessary for 50 mg. of manganese. It is evident that about 80 per cent more than the amount of bismuthate demanded by theory is required. I t is true that the amount of manganese oxidized by a known weight of bismuthate is slightly increased if the time of contact is lengthened, but in order to reduce the operating time to a
59
minimum the period of 1 minute was chosen. The ordinarily given directions to use “an excess” of bismuthate are of little help in gaging the amount necessary, because even in the cases where the amount of bismuthate was deficient some residue remained. STABILITY OF PERMANGANIC ACIDFORMED I n general, the decomposition of permanganic acid in nitric acid solution is promoted by high concentration of the permanganic acid itself, by an increase in the acidity of the solution, and by a rise in temperature. On the other hand, the oxidation by bismuthate takes place most readily in acid of high concentration-that is, in acid of from. 1.1 to 1.2 specific gravity, or 19 to 28 per cent by weight. For complete oxidation the amount of nitric acid in the solution can be varied within fairly wide limits, but most not be too low. Nitric acid of 1.135 specific gravity (about 22 per cent by weight) is generally used. The following tible shows the number of cubic centimeters of 0.1 N permanganic acid formed from equal portions of manganese solution, the time of contact, with the bismuthate having been constant (1 minute). TABLE11-EFFECT OF ACIDITY ON OXIDATION Acidity KMIIOI Per cent cc.
22.0 11 .o 7.0 5.5 4.0
45.44 45.45 43.13 40.70 35.32
It is obviously quite possible, when dealing with large quantities of manganese, that the original oxidation by bismuthate may go to completion, but that the permanganic acid formed may decompose before it can be determined, thus causing low and erratic results. The stability of permanganic acid solutions in different concentrations both of nitric acid and of permanganic acid was therefore determined in the following manner: Solutions of manganous nitrate were prepared of such strengths that on complete oxidation the normalities of the resulting solutions of permanganic acid would be approximately 0.025 N , 0.05 N , 0.1 N , 0.2 N , and 0.5 N . The solutions were oxidized by the requisite amounts of bismuthate and filtered through asbestos. I n order to avoid diluting the Solutions the asbestos filters were not washed. Aliquots were then taken a t different time intervals and used for determinations of the amounts of permanganic acid. All the solutions in this first series contained 22 per cent of nitric acid. In order to study the stability of permanganic acid in 11 per cent nitric acid, the quantity of manganese present was doubled, the oxidation was performed in 22 per cent nitric acid, but the solution was diluted with an equal volume of water before filtering. The nitric acid present was thus halved, while the permanganic acid was reduced to the required concentration. The normalities of the solutions formed were not exactly 0.025, 0.05, etc., but were sufficiently close to give the desired information, The normalities given in the first column were calculated from the f i s t titrations, made immediately after filtration. TABLE 111-STABILITYOF PERMANGANIC ACIDIN 22 PER CENT NITRIC ACID (TEMPERATTJRE 22’ C., OR 72O F J Strength of HMnOa Strength at Immediately after End of First --Filtration-IntervalTitraTitraNormaltion tion ity Cc. Minutes Cc.
0.0241 0.0477 0.0918 0.1800 0.4140
12.06 23.84 45.89 90.10 103.82
21 29 I9 24 20
Strength at End of Second -Interval-DecomTitraposition tion Per cent Minutes Cc. 11.96 0 83 39 11.86
23.74 45.50 87.00 97.10
0.42 0.85 3.33 4.55
45 38 44 37
23.49 45.08 81.72 90.58
Decomposition Per cent
1.66 1.68 1.77 9.30 12.80
It is evident that the rate of decomposition of permanganic acid solutions in 22 per cent nitric acid increases very rapidly
IND UXTRIAL AND ENGINEERING CHEMISTRY
60
when the concentration of permanganic acid rises above 0.1 N , and that it is at a minimum at about 0.05 N . I n the series with 11 per cent nitric acid the concentration of permanganic acid formed was not carried so high as 0.5 N , as the percentage decomposition would evidently be too great in practice. TABLE IV-STABILITY
OR PERMANGANIC ACID I N 11 P E R CENT
(TEMPERATURE 22" C., Strength of HMnOi Immediately after -FiltrationFirst Normalitv
0.0248. 0.0498 0.0961 0.1690
Titration cc.
24.58 49.77 96.06 84.50
OR
Titration at End of 20 DecomMinutes position Cc. Percent 0.24 24.52 0.12 49.71 0.30 95.77 1.36 83.65
NITRICACID
72' F.) Titration a t End of 40 DecompoMinutes sition Cc. Per cent 24.49 0.37 49.67 0.18 95.21 0.58 82.55 2.36
Obviously, the concentration of the manganese must be kept below 0.1 N , and as the results show that 0.05 N permanganic acid suffered the least decomposition, such conditions should be adopted that the strength of the permanganic acid after filtration does not greatly exceed this figure. Inasmuch as the filtration can ordinarily be made in 3 minutes a t the outside, the decomposition occurring during this period should be negligible. The conditions necessary for securing complete oxidation of large quantities of manganese and for preventing the permanganic acid from undergoing any appreciable decomposition during the subsequent filtration are summarized below. CONCENTRATION OF NITRICACID-The manganese should be present in a solution containing from 11per cent (specific gravity 1.062) to 22 per cent (specific gravity 1.135) by weight of nitric acid. If the concentration of nitric acid falls much below 11 per cent, the oxidation of the manganese will not be complete unless the time of shaking be increased to more than 1 minute. CONCENTRATION OF MANGANESE-Asolution of permanganic acid containing about 0.05 gram of manganese per 100 cc. has the maximum stability, but the weight of manganese can be increased to 0.1 gram in 100 cc. without danger of any material decomposition occurring during the time required for filtering off the excess of bismuthate. When the concentration of manganese rises much above 0.10 gram per 100 cc. the rate of decomposition of the permanganic acid is unduly rapid. ANOUNT OF SODIUM BISMUTHATE NECESSARY-Approximately 26 grams of sodium bismuthate (79 per cent NaBiOa) must be used for 1 gram of manganese. TIMEOF OXIDATION-shaking for 1 minute is sufficient to insure complete oxidation of the manganese to permanganic acid provided the foregoing conditions are adhered to.
UNIFORMITYOF OXIDATIONWITH VARYINGAMOUNTS MANGANESE
OF
Manganous oxalate (MnCz04.2Hz0)was found to be an excellent material for use in studying the uniformity of oxidation of varying weights of manganese. The fact that, owing to the presence of small amounts of metals other than manganese, the two samples employed in these particular experiments contained somewhat smaller percentages of mangtnese than the theoretical (based on the sodium oxalate standard), did not affect their suitability for this phase of the work. Manganous oxalate has the great advantage over manganous sulfate or a standard manganese ore in that it is nonhygroscopic and can therefore be weighed directly on a watch glass. Furthermore, the low percentage of manganese in the salt (30.69 per cent) makes errors in weighing less important than with a manganese ore. The manganese in the oxalate was determined in the following manner: The sample was first decomposed by heating with a small amount of nitric acid (specific gravity 1.42)) diluted somewhat with 22 per cent nitric acid (specific gravity 1.135), and the solution treated with small amounts of bismuthate until manganese precipitated, thus destroying the last traces of oxalate. After having boiled the liquid a few minutes,
Vol. 16, No. 1
sulfurous acid was added drop by drop until the precipitated manganese dioxide had dissolved. The boiling was then continued until nitrous h m e s had been completely expelled, the solution finally being diluted with nitric acid (specific gravity 1.135). The manganese was present in a concentration of 1mg. per cubic centimeter. The solution was cooled to about IO" C., the calculated amount of bismuthate added (2.6 grams per 100 mg. manganese), and the solution thoroughly agitated for 1 minute. After dilution with an equal volume of water, the permanganic acid formed was filtered through asbestos, and the filter washed with 3 per cent nitric acid. A weighed amount of ferrous ammonium sulfate was added to the filtrate, and the excess titrated with 0.1 N potassium permanganate. The manganese value of the ferrous ammonium sulfate was determined by titration with 0.1 N potassium permanganate that had been standardized against sodium oxalate from the Bureau of Standards. TABLE V-UNIFOWITY Weight of Sample
Gram
0.2026 0.4032 0.6031 0.8051 1.0054 1.2034 0.3327 0.6654 0.9981 1.3308 1.6635
OF OXIDATION WITH VARYING AUOUNTS OF
MANGAN~SE
Volume of Solution
Weight of Manganese Foend Gram Manganous Oxalate, B 60 0.0611 120 0.1215 180 0.1821 240 0.2428 300 0.3030 360 0.3625 cc
.
Percentage of
Manganese Found
30.17 30.14 30.20 30.16 30.14 30.13 AVERAGE 30.16
Manganous Oxalate, D 0.1006 200 0.2015 300 0.3025 400 0,4023 500 0.5045 AVERAGE 100
30.25 30.28 30.30 30.23 30.33 30.28
These results leave nothing to be desired, and conclusively show that the oxidation is uniform with amounts of manganese up to 0.5000 gram. It is believed that the most important factor in attaining such results consists in keeping the manganese present a t a fairly definite concentration, the use of a sufficient amount of bismuthate being naturally assumed. CORRELATION OF VALUE OF PERMANGANATZ USED FOR TITRATION WITH A N ABSOLUTE STANDARD In order to determine the value of the permanganate in terms of manganese, manganous sulfate prepared in the following manner was used: Potassium permanganate (the ordinary C. P. product) was reduced in the presence of sulfuric acid with a little less than the calculated amount of oxalic acid, and the manganese dioxide formed was atered off and discarded. The solution of manganese sulfate was treated with ammonium carbonate and the resulting manganese carbonate was filtered and washed free from sulfates by decantation. This precipitate was added to a boiling solution of oxalic acid, and the manganous oxalate formed was filtered and washed free from acid with distilled water. This product was converted to the sulfate by heating to constant weight a t 480" to 520" C., with an excess of sulfuric acid. An accurately weighed amount of the pure manganous sulfate (2.7536 grams of MnS04, equivalent to 1.0018 grams of manganese) was dissolved and made up to 1 liter with nitric acid (specific gravity 1.135). One hundred and 200-cc. portions of this solution were oxidized with sodium bismuthate, filtered, and reduced by addition of accurately weighed amounts of ferrous ammonium sulfate, the excess of which was determined by means of 0.1 N permanganate that had been standardized against sodium oxalate. The relation between the ferrous ammonium sulfate and the permanganate was carefully determined. The results obtained, shown below, confirm Blum's statement that either manganous sulfate or sodium oxalate may be used
INDUSTRIAL A N D ENGl‘NEERING CHEMISTRY
January, 1924
as the primary standard for the bismuthate method, or expressed in another form, that the manganese is quantitatively oxidized to the heptavalent state. Although in a sense these figures are merely confirmatory of Blum’s work, they are more important than this because they show that even with 200 mg. of manganese present the oxidation is theoretically complete within the limits of error. As the results in Table VI show that the oxidation is uniform with quantities of from 60 to 500 mg., there can remain no doubt that completeness of oxidation is possible with comparatively large quantities of manganese-a great advantage in the determination of manganese in products containing high percentages of the element. T A B L B VI-STANDARDIZATION
OF PERMANGANATE AGAINST
SULFATE AND SODIUM OXALATE
MnSOr
Gram _.-
0.2754 0.2754 0.5507 0.5507
Manganese Gram _. ~
0.1022 0.1002 0.2004 0.2004
KMnOi
1 CC. KMnOr = gram Mn 91.05 0.001100 91.05 0.001100 182.5 0.001098 182.35 0.001098 AVERAGE0.001099 cc.
MANGANESE
__ .
1 0 0
-
KMnOr
= gram Mn from NazCzOn
.... .... .... ....
0.001097
Table VI1 gives the results on varying amounts of oxalate, the actual manganese content having been calculated from the manganese sulfate obtained from a definite amount of manganese oxalate. TABLIE VII-ADDITIONALDATAREGARDING UNIFORMITY Calculated Weight of M n Used Gram
0.0200 0.0200 0.0200 0.0300 0.0300 0.0300 0.0501 0.0501 0.0501 0.0501 0.0501 0.1002 0.2019 0.2063 0.2155
OF OXIDATION
-Weight of Manganese FoundNapCzOa Standard MnS04 Standard Gram Gram
0.0200 0.0200 0.0200 0.0300 0.0300 0.0298 0.0502 0.0499 0.0501 0.0501 0.0501 0.1001 0.2015 0.2058 0.2152
0.0200 0.0200 0.0200 0.0300 0.0300 0.0298 0.0503 0.0500 0.0502 0.0502 0.0502 0.1003 0.2019 0.2062 0.2156
CONDITIONS FOR OXIDATIONOF MANGANESE I n practice the oxidation is carried out in nitric acid solution, preferably of about 22 per cent “08 by weight (specific gravity 1.135). The solution should be free from all substances that reduce permanganate, as the resulting manganous salt would gradually react with the permanganic acid from the oxidized manganese and precipitate manganese dioxide, which would not be further oxidized by the bismuthate. The temperature of the solution should not exceed 25’ C., and should preferably be lower. When large quantities of manganese are being determined it is necessary to weigh out roughly (* 0.05 gram) the amount of Eismuthate required, using 2.6 grams of 80 per cent sodium bismuthate for every 100 mg. of manganese. Generally, the amount of manganese present is known t o be within certain limits; if not, a small trial portion of the solution may be used for oxidation in the manner described under “Analysis of Manganese Ores.” Failure to have a t least the quantity of bismuthate specified will result in incomplete oxidation; excess over this amount can do no harm except perhaps t o slow up the filtration. With thorough agitation, oxidation is complete in 1minute. The solution should contain about 0.001 gram of manganese per cubic centimeter, and if necessary must be diluted accordingly, the acidity being kept constant. As previously indicated, this concentration has been chosen to obtain maximum stabili1,y of the permanganic acid. Sulfates or small amounts of sulfuric acid do not interfere, but chlorides must be absent. If chlorides are present in the original solution, they are removed by evaporating with sulfuric acid. The residue is
61
dissolved in a small amount of water and the solution is evaporated to fumes a second time to insure the removal of every trace of chloride. The only common metals that seriously interfere with the determination are cerium, cobalt, and sexivalent chromium. A method for the determination of cerium outlined by Metzger’ is exactly the same in principle as the bismuthate method for manganese, Any cerium present must therefore be separated as oxalate in acid solution, and the oxalic acid in the filtrate destroyed by evaporation with sulfuric and nitric acids as a preliminary to the determination of manganese. The pink color produced by large amounts of cobalt interferes with the titration of permanganic acid. This can be overcome by separating the manganese from the bulk of the cobalt by precipitating it with sodium or potassium chlorate. While trivalent chromium is in hot solution oxidized to the sexivalent state by bismuthate and by permanganic acid, the error caused by small amounts of trivalent chromium is not appreciable provided the solution is kept cold (10’ C.), and is oxidized, filtered, and titrated as rapidly as possible. When more than a small percentage of chromium is present, it should be separated from the manganese by one of the several methods that have been proposed. Precipitation of the manganese from a nitric acid solution with sodium or potassium chlorate with subsequent filtration does not effect complete removal of chromium, but is useful in some cases. Fusion with sodium peroxide followed by filtration will give a complete separation, manganese remaining in the residue as oxide and chromium passing into the filtrate as sodium chromate. Watterss precipitates chromium and ferric iron with zinc oxide and determines manganese in the filtrate, while Cain* precipitates chromium and vanadium from a ferrous solution with cadmium carbonate and analyzes the filtrate for manganese. Sexivalent chromium interferes with the determination of manganese by the bismuthate method and must be reduced to the trivalent condition prior to the h a 1 oxidation with bismuthate. Although any vanadium present is reduced by the ferrous sulfate added during the determination, it is re-oxidized by an equivalent amount of permanganic acid during the back titration, the manganese titration as a consequence being unaffected. Provided accurate volumetric apparatus is available, it is usually preferable to make the manganese solution up to a definite volume and to work on an aliquot portion. The solution should always be given a preliminary oxidation with’ bismuthate before being made up to volume. Rismuthate is added to the hot solution in small portions until manganese dioxide precipitates, the liquid is boiled for 5 minutes, and then sulfurous acid is added drop by drop until the precipitate has dissolved. If sexivalent chromium is present, enough sulfurous acid must be added to reduce it to the trivalent form. After the solution has been boiled for several minutes longer to expel oxides of nitrogen, it is ready for dilution. It may be diluted with water, in which case the proper amount of concentrated nitric acid must be added later, or with nitric acid of 1.135 specific gravity. If the addition of concentrated nitric acid is made later, about 28 cc. of acid (specific gravity 1.42) should be present in every 100 cc. The proper weight of bismuthate is added to the cool solution, which must have approximately the concentration of , manganese recommended (0.001 gram per cubic centimeter) and contain the necessary amount of nitric acid. The solution is agitated for 1 minute, diluted with an equal volume of water, and filtered through asbestos. A suitable filter consists of a 5qm. (2-inch) alundum plate resting in a large funnel, and 7 6
J . Am. Chem. SOG., 81, 523 (1909). Met. Chem. Eng., 9,244 (1911). THISJOURNAL, 3, 630 (1911).
62
INDUSTRIAL A N D ENG[INEERINGCHEMISTRY
Vol. 16,'No. 1
covered with a layer a t least 0.6 cm. (I/d inch) deep of acid- and add bismuthate in small (about 0.05 gram) portions, washed asbestos. The filter is washed with 3 per cent nitric until a permanent precipitate of manganese dioxide forms. acid until the washings are absolutely colorless. Permanganic Any organic matter is thus destroyed and the excess of hyacid equivalent to the manganese originally preserit is now in drogen peroxide removed. Boil for 2 or 3 minutes, and the filtrate. then add sulfurous acid drop by drop until the solution clears. Boil the solution for 5 minutes, and filter it into a DETERMINATION OF PERMANGANIC ACID 500-cc. volumetric flask. Wash the siliceous residue well Ferrous ammonium sulfate is used to reduce the perman- with water and ignite it in platinum. Treat the residue with ganic acid formed. It is added in solid form, weighed to several drops of sulfuric acid (specifia gravity 1.84) and *0.5 mg., just before the determination is started. This suEcient hydrofluoric acid to dissolve the silica, and evaporate salt is preferable to ferrous sulfate, as it goes into solution the solution until it fumes. Dissolve the residue in water more readily. The manganese value of the ferrous salt and add to the solution in the flask. Bring the solution to a must be known, and for this purpose 5.0000 grams (*0.5 mg.) temperature of about 20" C. and make it up to the mark are titrated with the standard permanganate used. This with water a t this temperature. titration should be made in sulfuric acid solution. If the With artificial manganese dioxide, where the weight of salt is kept in a well-corked bottle, the standard will suffer insoluble residue is insignificant, or in case the residue from practically no change, and having once been well mixed and an ore is flocculent and not sandy, the treatment with hystandardized may be used indefinitely. If preferred, a 0.1 N drofluoric and sulfuric acids may be omitted and the ore solution of ferrous ammonium sulfate may be used instead of solution rinsed directly into the flask. Any barium in the the solid,salt. ore will precipitate when the sulfuric acid solution of the The excess of ferrous saIt is now titrated with a standard- residue is added to the main solution, but the barium sulfate ized solution of potassium permanganate, preferably of about does not interfere with the subsequent operations. 0.1 N strength. The permanganate may be standardized TRIALDETERMINATION-AS it is desirable that the back against Bureau of Standards sodium oxalate, according to titration with permanganate be not too great (say, from 10 McBride'slO recommendations, by means of pure manganous to 20 cc.), it is best, when ores of unknown manganese content oxalate as hereinafter described, or against pure anhydrous are being analyzed, to make a rough preliminary determinamanganous sulfate. Owing to the difficulty of preparing tion of the amount of manganese present, so that the amount the latter salt so that it is of theoretical composition, the of ferrous salt added may not be excessive. For this purfirst two methods of standardization are preferable. After pose transfer 25.0 cc. of the well-mixed solution with a pipet the normality of the solution against sodium oxalate has been to a 300-cc. Erlenmeyer flask and add 12 cc. of nitric acid determined, the theoretical factor-via., 1cc. 0.1 N KMn04 = (specific gravity 1.42) and about 13 cc. of water. Cool this 0.001099 gram of manganese-may be used. solution, add 1.7 grams of bismuthate, agitate the mixture DETERMINATION OF MANGANESE I N MANGANESE ORES for 1 minute, dilute with 50 cc. of water, and filter through asbestos, washing the residue with dilute (3 per cent) nitric Descriptions of the application of the bismuthate method acid. Add 2.5 grams (weighed) of the solid ferrous ammoto the determination of manganese in manganese ores, ferro- nium sulfate to the filtrate and titrate back with the 0.1 N manganese, and manganese metal are given in the following permanganate. Calculate in the usual manner the weight paragraphs. The adaptation of the method to other products of manganese present in the 25-cc. portion. As 100 cc. will high in manganese is easily made after the operator becomes be used in the actual determination, multiply the result by 4, familiar with the conditions necessary. and calculate approximately the amount of bismuthate necesREAGENTS REQUIRED-(~) Concentrated nitric acid (specific sary (26 grams for 1gram for manganese) and also a weight gravity 1.42), freed from nitrous oxide by passing air through the of ferrous sulfate that will give from 10 to 20 cc. in the back solution for half an hour. If air from a compressor is used it titration. The bismuthate is weighed out roughly, and the must be freed from oil and dust. ( 2 ) Nitric acid of specific gravity 1.135, made by adding 500 cc. necessary ferrous sulfate weighed out to within half a milliof the above acid to 1300 cc. of water. gram just preceding the titration. * (3) Dilute nitric for washing, prepared by adding 30 cc. of FINALDETERMINATION-Transfer two 1 o o - C C . aliquot the concentrated acid described above to 1liter of water. (4) Sodium bismuthate. This reagent generally contains portions with a pipet to 750-cc. Erlenmeyer flasks and add approximately 80 per cent of NaBiOs. If there is any doubt as 50 cc. concentrated nitric acid and 50 cc. of water to each. to its oxidizing power, it may be tested as follows: (Total volume, 200 cc.) Cool the solutions (with ice, if One-half gram is shaken up with 4 grams of potassium iodide possible) and add the calculated amount of bismuthate all and a littlc water in a stoppered flask. Fifteen cubic centimeters of hydrochloric acid (specific gravity 1.20) are added and the at once. Agitate the contenfs of the $ask briskly for I minute, solution is allowed to stand in the dark, with occasional shaking, add 200 cc. of cold water, and filker through asbestos, washuntil the bismuthate has entirely decomposed. The solution is ing the residue with dilute nitric acid (solution No. 3) until the diluted to 300 cc. and titrated with 0.1 N sodium thiosulfate, washings do not show the slightest trace of pink. starch being used as indicator. Place the weighed ferrous salt in a liter beaker and add the 1 cc. of 0.1N Na~S203= 0.0140 gram NaBiOs contents of the suction flask to it. Stir thoroughly until the ( 5 ) Ammonium persulfate (C. P.). (6) Ferrous ammonium sulfate. permanganic acid has been decolorized and all the salt dis(7) Hydrogen peroxide (3 per cent). solved. Titrate a t once with the standardized 0.1 N potas(8) Sulfurous acid. A freshly prepared solution of sulfur sium permanganate to add faint pink. dioxide in water. TYPICAL ANALYSIS-TWOgrams of ore were dissolved and (9) Standardized 0.1 N potassium permanganate. made up to 500 cc.; two 100-cc. aliquot portions were oxiSOLUTION OF THE ORE-Grind the sample to pass 100 mesh dized and 9 grams of ferrous salt added to reduce the permanand dry a t 120' C. for 1 hour. Dissolve 2.0000 grams (A 0.0002 gram) by boiling with about 40 cc. of nitric acid ganic acid formed. TABLE VIII-MANGANESE I N M A N G A N E S EORE (1 : 1) in a 400-cc. beaker covered with a clock glass, adding Aliquot Aliquot No. 1 No. 2 hydrogen peroxide in small portions until the violent evolu20.2 Back titration, cc.. . . . . . . . . , , . , , , . . . . . . . . 20.1 tion of oxygen is over and no black particles of ore remain. Equivalent 228.6 of ferrous salt, c c . , , . , , . ... . . . . . 228.6 208.4 208.5 Rinse the clock glass and sides of the beaker with hot water, Difference, cc.. . . . . . . . . . . . . . . . . . . . . . . . 0,2290 0 2291 Weight of manganese, gram. . . , . . . . . . . . . . 57.24 10 J . A m . Chem. Soc., 51, 393 (1912). Percentage of manganese. . . , , . . . . . . . . . . . . 57.26
I N D V S T R I A L A N D ENGINEERING CHEMISTRP
January, 1924
ANALYSISOF FERROMANGANESE The weight of sample used is governed by the manganese content; for 80 per cent ferromanganese from 0.25 to 0.30 gram niay be used. As there is no difficulty in obtaining a uniforni sample, it is preferable to weigh out individual portions of the 100-mesh sample for the determination, instead of using an aliquot part of a large sample. The following procedure as regards the quantity of acid and final volume presupposes the presence of about 0.2 gram of manganese. When working with high-carbon ferromanganese, dissolve the sample in 60 cc. of nitric acid (specific gravity 1.42) and boil in a flask or covered beaker until nitrous fumes cease to be evolved. If the sample contains over 1 per cent of chromium, it is necessary to dilute the solution with an equal volume of water, filter, ignite the residue, and fuse it with a little sodium carbonate, dissolving the melt in the least possible quantity of nitric acid and adding it to the main solution. Oxidize the carbon present by adding ammonium persulfate, a little a t a time, until a total of from 2 to 2.5 grams has bern introduced. Boil the solution about 10 minutes, and then add small amounts of bismuthate to the boiling liquid, until a precipitate of manganese dioxide has formed. Dissolve the precipitate by the addition of sulfurous acid, drop by drop, adding an excess of 1 cc. after the precipitate has dissolved to reduce any chromium to the trivalent form. After having boiled the solution for 5 minutes, bring it to a volume of 200 cc., and cool with ice. This cooling is essential in order that any chromium may not interfere, as it would be oxidized by the bismuthate if the solution were at elevated temperatures. The manganese is then oxidized with bisniuthate and determined as described under “Analysis of Manganese Ore.” The following data are from typical determinations on a sample of standard high-carbon ferromanganese: TABLE IX-MANGANESEIN FERROMANGANESE KMn04 Equiv0.1 N
Weight of Ferrous Sample Salt G. G.
0.2500 0.2500 0.3000
7.5 7.5 9.0
alent of Ferrous Salt cc
Back Titration cc.
KMnO4 Consumed Cc.
Per cent Manganese
191.3 191.3 229.2
13.4 13.4 15.7
177.9 177.9 213.5
78115 78.15 78.19
.
Low-carbon ferromanganese is dissolved directly in nitric acid of 1.135 specific gravity (about 1 cc. for every milligram of manganese present). After preliminary oxidation and reduction of the solution, it is made up to the original volume with nitric acid (specific gravity 1.135) and cooled as a preliminary to the oxidation and determination of the manganese.
AKALYSISOF MANGANESE METAL Dissolve 0.2500 gram in 250 cc. of nitric acid (specific gravity 1.135) in a 750-cc. Erlenmeyer flask provided with a cut-off funnel or some similar device to prevent loss by spraying, and make a preliminary oxidation with bismuthate, subsequently reducing with sulfurous acid. If the carbon is high (4 per cent) oxidation with ammonium persulfate should precede the bismuthate oxidation. Dilute the solution to a volume of 250 cc. by adding nitric acid (specific gravity 1.135), cool with ice, and finish the determination as pre~iouslyoutlined. About 6.5 grams of sodium bismuthate are necessary for the oxidation and 9 grams of ferrous salt will reduce the permanganic acid resulting from a 0.2500 gram sample of 95 per cent manganese metal. TABLE X-MANGANESEIN MANGANESE METAL KMnOa Equiv0.1 N
Weight of Ferrous Sample Salt G. G.
No.
1 0.2000 2 0.2500 3 0.2500
8.000 9.000 9.000
alent of FerBack rous Salt Titration cc. cc.
203.8 229.2 229.2
28.5 10.0
10.2
KMnOa Consumed Cc.
Per cent Manaanese
175.3 219.2 219.0
96T29 96.32 96.24
63
BIBLIOGRAPHY Schneider, “Methode zur Bestimmung des Mangans,” Dingtms poly-
fech. J . , 869;224
(1899).
Reddrop and Ramage, “The Volumetric Estimation of Manganese,” J . Chem. SOC.(London), 67, 268 (1895). Compredon, “Sur le dosage rapide des principaux elements des produits siderurgiques,” Res. Chim. Ind., 9,306 (1989). Mignot, “Dosage volumetrique d u manganese dans les Fers, fontes and aciers,” Ann. chim. anal., 6, 172 (1900). Ibbotson and Brearly, “Analysis of Ferro-Silicon and Siliconspiegel,” Chem. News, 82, 269 (1900). Ramage, “Volumetric Estimation of Manganese,” Ibid., 84, 209, 269
(1901). Ibbotson and Brearly, “Volumetric Estimation of Manganese,” Ibid., 84, 247, 302 (1901). Dufty, “Volumetric Estimation of Manganese,” Ibid., 84, 348 (1901). Ibbotson and Brearly, “Volumetric Estimation of Manganese,” Ibid., 86, 59 (1902). Jaboulay, “Dosage du manganese dans les Aciers,” Rev. gen. chim., 6 ,
119 (1903). Blair, “The Bismuthate Method for the Determination of Maneanwe,”
J . A m . Chem. Soc., 26, 793 (1904). Metzger and McCracken, “A New Volumetric Method for the Determination of Manganese,” Ibid., 82, 1250 (1910). Brinton, “The Determination of Manganese by the Sodium Bismuthate Method,” J. Ind. Eng. Chem., 3,237,378(1911). Hillebrand and Blum, “The Determination of Manganese by the Sodium Bismuthate Method,” Ibid., 8, 374 (1911). Cain, “The Determination of Manganese in Vanadium and ChromeVanadium Steels,” Ibid., 8, 630 (1911). Cahn and Little, “Waldemar Fischer’s Modification of Volhard’s Method for the Volumetric Estimation of Manganese, and Its Comparison with Other Well-Known Methods,” Analyst, 86, 52 (1911). Little, “The Estimation of Manganese by the Bismuthate Method,”
Analyst, 37, 564 (1912). Blum, “Determination of Manganese as Sulfate and by the Sodium Bismuthate Method,” J. A m . Chem. Soc., 84, 1379 (1912). Demorest, “The Bismuthate Method for Manganese,” J. I n d . Eng.
Chem., 4, 19 (1912). Gortner and Rost, “The Determination of Total Manganese in Soils;’
Ibid., 4, 522 (1912). Kinder, “Manganbestimmung in Eisen und Stahl nach dem Wismutatverfahren,” Stahl u. Eisen, Si’, 197 (1917).
Eminent Chemists From time to time there have come to us requests for sources of portraits of eminent American chemists prepared for framing and suitable for decorating laboratories, lecture rooms, and the halls of educational institutions. Diligent search having shown that very few Americans had been included in such collections of portraits as had been made by publishers, we persuaded our associate editor to undertake the preparation of such a collection, calling upon a number of men to assist in compiling a list of those t o be included in the first series. This work has been completed and, if advance subscriptions warrant, a set of thirty-three portraits, beautifully done on the best grade of paper, will be available in a loose-leaf binder, these portraits being interleaved with short sketches of the work of each of the subjects. The portraits themselves are 4l/2 x B1/2 inches on sheets a1/2 x 10 inches. Announcements will be made soon as t o prices and other details. We give below the list of the men included in this set and believe that if a larger number of people become interested in the personalities which have so greatly contributed to the advancement of chemistry, a historical and cultural background will be estabished which cannot fail to make our science still more attractive. Baekeland, L. H. Bancroft, W. D. Boltwood, B. B. Booth, J. C. Chandler, .C. F. Chittenden, Russell H. Clarke, F.W. Cottrell, F. G. Cooke, Josiah P. Franklin, E. C. Gibbs, J. Willard Gibbs, Wolcott Gomberg, Moses Hare, Robert Hillebrand, W. F. Hunt, T. Sterry Langmuir, Irving
Lewis, G. N. Mallett, J. W. Morley, E. W. Noyes, A. A. h-oyes, W. A. Priestley, Joseph Remsen, Ira Richards, T.W. Rumford, Count Silliman, Benjamin, the Elder Smith, Edgar Fahs Smith, J. Lawrence Stieglitz, Julius Van Slyke, Donald D. Whitney, W. R. Wiley, H. W.
