V O L U M E 2 7 , NO. 9, S E P T E M B E R 1 9 5 5 Table
1433
IV. Recovery of Known Amounts of Oxygen in Calcium Metal
-
Calcium, Addeda Grams (A) 2.004 28.5 2.001 14.6 4.000 7.1 5.002 7.1
In alcoholb
(B)
7.5 38.4 11.3 19.0
Oxvnen. ” _ . Me. In Total metalc (A B (C) C) 16.011.1 52.0 16.0 f 1.1 69.0 32.012.3 50.4 40.0f2.8 66.1
++
Found 53.0 69.3 52.3 63.9
Difference +1.0 +0.3 +1.9 -2.2
a Added a s calcium oxide. b Calculated from water found in a n aliquot of alcohol and corrected for average blank difference of -0.36 mg. a s found in Table I. C Average of eight determinations. .Metal was heterogeneous.
I n Table I1 it can be seen that 2.6 mg. of ouygen, added as calcium oxide, can be determined with an error of less than 5%. For a &gram sample, this is equivalent to the determination of 0.05% oxygen in calcium metal. Because of the relatively slov reaction of calcium with atmospheric water and ouvgen as compared to sodium, no elaborate precautions must be taken in weighing and transferring the calcium to the reaction flasl~. These operations, however, should
be carried out as quicklv as possible. However, in production sampling a t thp manufacturing plant, the metal taken for analysis should be sealed immediately in a dry inert atmosphere since days may elapse before an analysis is made. Moreover. samples in containers once opened show a continuous increase in oxygen content unless this precaution is taken. For the currently available calcium metal, as a result of sample heterogeneity, several determinations are required. LITER.ATURE CITED (1) k’oulk, C.
W., and Bowden, A. T., J . Am. Chem.
Soc., 48, 2045
(1926). (2) Gunte, A , and Roderer, G., Compt. Rend., 142, 400 (1906). (3) AIitchell. J., Jr.. and Smith, D. XI., “Aquametry,” p. 67, Interscience, N e w York, 1948. (4) Tbid.,p. 86. ( 5 ) I b i d . , p. 248. (6) Pepkorvitz, L. P., and Judd, W. C., ANAL.CHEW,22, 1283 (1950). (7) White, J. C., Ross, W. J., and Rowan, R., Jr., Ibid., 26, 210 (1984). ( 8 ) Whitmore, F. C., “Organic Chemistry,” p. 105, Van Nostrand, Kew York, 1942. (9) Williams, D. D.. and Miller. R. R., AXAL.CHEM.,23, 1865 (1951). RECEIVEDMarch 18, 1955.
Accepted RIay 16, 1955.
Determination of Wolframite in SILVE KALLMANN Ledoux & Co., Inc., Teaneck,
N. 1.
Both the natural and artificial forms of scheelite (a calcium tungstate with the formula CaWO4) must be l o w in iron and manganese to meet government specifications. These elements indicate the presence of the iron and/or manganese tungstate mineral wolframite Fe(hIn)WO, which is only slightly soluble in dilute acids, thus obviating total extraction of the tungsten in industrial processes. The method described here suggests solution of the sample in hydrochloric acid in the absence of oxidizing agents and determination of the iron(II), the form in which iron exists in wolframite. Other hydrochloric acid-soluble minerals found in scheelite either are present in the trivalent form or are oxidized by a heating at 400” C. for 4 hours. Experiments are described which indicate that virtually all of the manganese found in scheelite is present as the tungstate. The proposed method is expected to aid in avoiding controversies in the tungsten industry concerning the actual amount of wolframite found in scheelite.
OLFRAMITE, an iron and/or manganese mineral of the formula Fe(;Iln)W04, is less soluble in dilute acids than the calcium tungstate mineral scheelite ( CaW04). Therefore. Material Purchase Specifications of the General Services ildministration covering the purchase of Class I, Katural and Synthetic Scheelite, under the Xational Stockpiling Program ( 2 ) strictly limit the amount of wolframite permissible in scheelite These specifications of the General Services Administration are based on its assumption that all the manganese in a scheelite is present as hubnerite and all the iron as ferberite. Hubnerite is defined principally as manganese tungstate with no more than 20y0 of the tungsten present as ferrous tungstate, while ferberite is described as FeWO, with no more than 20% of the tungsten as manganese tungstate. Combinations of hubnerite and ferberite in varying proportions thereby form wolframite.
Based on a 23.41y0 manganese oxide (MnO) and a 76.59% tungstic oxide (\V03) content, 1% of manganese found in scheelite is calculated to be due to 5.52% of manganese tungstate, resulting in a penalty for 4.22% of tungstic oxide. Fortunately, the amount of manganese found in scheelite rarely exceeds 0.20% and therefore oEers less of a problem than does iron, which frequently is present in excess of 1%. In the case of iron, based on a 23.64y0 ferrous oxide and 7G.3Gq6 tungstic oxide content, 1% of iron found in scheelite is calculated to be due to 5,44Y0 of ferrous tungstate resuiting in a deduction of 4.15% of tungstic oxide from t,he total amount of tungstic acid found. FERBERITE
The assumpt,ion that A! t,he iron in a scheelite is present as ferberite appears to be unwarranted. On many occasions, the yellow color of ferric chloride n-as noted when dissolving scheelite in concentrated hydrochloric acid in absence of air and oxidizing agents. Because iron is present in ferberite in the iron(T1) form ( I ) , any t,rivelent iron obviously denotes the presence of iron minerals ot,her than ferberite. Ten wolframite concentrates originating from various locations throughout the world were recently analyzed in this laboratory for the three major components, using standard methods of ttnalyeis (S, 6). The result,s presented in Table I positively demonet’rate that wolframite concentrates frequently contain an excess of iron andlor manganese to satisfy the formula Fe(h h ) w 0 4 . In addition to the iron introduced into scheelite from wolframite, either as part of the mineral or as cont,aminant,,the scheelite concentrate may contain various other iron minerals which could not he removed during the concentration process. KO chemical methods found in the literature differentiate between the iron of \volfraniite and that of other iron minerals. I n the past, the Bureau of AIines has provided :t very limited service by submitting the most controversial samples to microscopic t,ests including grain count. Since the need for a routine procedure has become apparent, an attempt was made to develop a rapid chemical method.
1434
ANALYTICAL CHEMISTRY
Table I. Sample No.
4 5 6 7 8 9 10
Comparison of WOa by Analysis and by Calculation
Fe Found,
%
F e X 4.15 = % \\'Os,
%
15.45 8.00 11.70 15.70 17.42 16.10 12.25 6.59 10.45 7.11
64.12 33.20 48.56 65.10 72.29 66.82 50.84 27.35 43.37 29.51
hln &In X 4.22 WOs, 70 Found, = % WOa, CalcuBy lated analysis % 70 1.65 6.96 71.08 66.15 10.67 45.03 78.23 68.61 32.20 80.76 70,98 7.63 77.95 74.31 3.03 12.79 81.36 2.15 9.07 68,40 76.82 2.37 10.00 68.21 82.24 7.44 31.40 69.33 33.00 60.35 7.82 46.97 32.75 76.12 7.76 72.79 65.68 8,57 65,66 36.17
Table 11. Accuracy of Proposed Method Fe -4dded to 1 Grain of Scheelite, M g . 1.6 1.6 1.6 3.1 3.1 4.6 4.6 +
+
FeCt Found,
Mg.
1.8 1.4 1.5 3 2 2 9 4 2 4.6
Fe++ Added t o 1 G r a m of Scheelite, Mg. 4.6 4.6 7.6 7.6 7.6 15.2 15.2
Fe++ Found, Mg. 4.8 4.8 7.2 7.2 7.6 14.7 15.3
Principle of Proposed Method. The propose'l method is based on the fact that iron exists in wolframite in the iroii(I1) state ( I )which forms, in the absence of oxidizing agents, ferrous chloride upon treatment with concentrated hydrochloric acid. Other hydrochloric acid-soluble iron minerals-such as pyritp, siderite, and garnets-associated with wolframite or contaminating scheelite, either are present in scheelite in the trivalent form or can, upon heating for 4 hours a t 400" C., be converted to thr trivalent state. The method does not anticipate the presence of inetallir iron (from crushing or grinding equipment) or magnetite. both of which should be removed, if present, with the help of a magnet.
%FECI
Figure 1.
Ovidation rate of iron(I1) in ferberite at various temperatures
Apparatus and Reagents. Burrell high-temperature electric furnarr, thermostatically controlled or equivalent. Standard Potassium Dichromate Solution, 0.13- (1 ml. = 5.581 mg. Fe).. Dissolve 4.9035 grams of KBS No. 136 in water, transfer to 1-liter volumetric flask, and dilute to the mark with water. Standard Potassium Dichromate Solution, 0.0112'. Transfer 100.0 ml. of 0.1N standard potassium dichromate solution t o a 1-liter volumetric flask and dilute to mark with water. Sodium Diphen,vlamine Sulfonate Indicator. Dissolve 100 mg. of the reagent in 100 ml. of cold water. Procedure. Transfer approximately 5 grams of the finely pulverized sample (-200M) t o a 20- to 30-ml. round-bottomed porcelain crucible. Heat in a thermostatically controlled furnace, with free access of air, for 4 hours a t 400" C., removing the crucible once every hour from the furnace and mixing the sample. Since the 400" C. roasting procedure provides for the oxidation
of ferrous-iron minerals soluble in hydrochloric acid, other than wolframite, particularly pyrite and siderite, this step may be omitted in the known absence of such compounds. Cool in a desiccator, weigh 1-gram portions into 500-ml. Erlenmeyer flasks, add 100 ml. of concentrated hydrochloric acid, and immediately close the flasks u-ith rubber stoppers containing a glass tube extending on the outside to the bottom of the flask. Seal the end of the tube with a solution of hot water containing a little sodium bicarbonate, heat the flask3 on a hot plate t o boiling, and allow t o simmer gently for 45 minutes. Replace the beaker with the hot water (now saturated 11 ith hydrochloric acid) Rith a fresh beaker containing 10 grams of sodium bicarbonate dissolved in 250 ml. of hot water. Remove the flasks from the hot plate and cool t o below 15' C., always keeping the end of the glass tube scsled a i t h the solution of bicarbonate. Remove the stopper from the flask, add 100 ml. of cold water, previou41 ti d c d ~ y i dcoded, add 1 nil of the sodium diphenylamine indicator, and i m m e d i a t e l y titrate the ferrous iron, depending on the iron content, u i t h the 0 1 01 0 01.V p o t a s s i u m dichromate solution t o afaint purpleendpoint nhicah can be easily noticed in the presence I of the precipitated t 1111g s t i c oxide. One 8 4 niilliliter of the 0 01N a potassium dichromate sohition is equivalent to 0.0558% of iron in the ferrous state or 0,:30% of ferberite. A c c u r a c y of Proposed Method. Varibus q u a n t i t i e s of a sulfur-free wolframite, %FEt+ containing 7.60% Figure 2. Oxidation rate of iron(II) (determined iron(I1) in 10% wolframiteby solution of the scheelite mixtures at various sample in hydrochloric temperatures acid in absence of air, and titration with standard p o t a s s i u m dichromate solution) were mixed with 5-gram portions of a scheelite with an iron content of 0.0170. The material was heated a t 400" C. ; 1-gram portions were dissolved in hydrochloric acid and titrated Lvith standard potassium dichromate solution. The results are presented in Table 11. Experimental. Figure 1 s h o w the rate of oxidation of a sulfurfree sample of wolframite a t various temperatures and time intervals, Figure 2 indicat,es the effect of heat on a sample of scheelite which was intimately mixed \vith 10% by weight of wolframite. F i g x e 3 demonstrates the rate of oxidation of the two ferrous-iron minerals, pyrite and siderite, at various temperatures. Figure 1 shows that the iron(I1) of ferherite is not significantly oxidized h - a 4-hour heating a t 400" C.; Figure 2, that ferberite, when mixed with an excess of scheelite, is not affected to a large extent; Figure 3, t,hat t,he ferrous-iron minerals, pyrite and siderite are oxidized sufficiently and do not cause serioue positive errors when present in small quantities. Iron sulfide minerals, other than pyrite, are expected to react similarly.
Talde 111. Sample N O
Solubility of Wolframite-3Ianganese in 29'0 Acetic .kcid Containing Oxalic Acid
Total hfn Present I'olhard Method ( 8 ) , hlg.
2 3 4
;7
7
8 4
10
a
__
ManpaneseFound, M g . 1st 2nd 3rd extraction evtraction extraction 0 4 1 4 0.5 0 4 2 1 0 7 0 5 0 4 0 4 0 3 0.5 0 3 0.4 1 0 0 7 0 2 0 3 1 8 0 4 1 3 0 4 0.4 11 R 0 8 0.5 0 7 21.8
11 Manganese added in form of pyrolusite ore. -~
__
- .__~____
V O L U M E 2 7 , NO. 9, S E P T E M B E R 1 9 5 5
1435 proposed method, indicating the presence of 0.38 X 5.44 = 2.07% of ferberite. Additional tests indicated no errors when small amounts of ilmenite and columbite were added to scheelite. H~BNERITE
No methods are described in the chemical literature to distinguish manganese of hubnerite from that of other manganese minerals. Based on experiments indicating that hiibnerite is only slightly soluble in dilute acetic acid containing a small amount of oxalic acid, manganese from most manganese minerals was found to be soluble in the above medium.
I
XFEtt
Figure 3. Oxidation rate of iron(I1) in 50 to 50 mixture of pyrite and siderite at various temperatures
Oxidized iron minerals-such as hematite or limonite-do not interfere with the proposed method in the absence of reducing agents. Occasionally, ferrous-iron minerals other than pyrite or siderite, occur in small quantities in scheelite as gangue material. They are usually silicates, mainly garnets,'with either part of the soluble iron in the oxidized form or easily oxidizable by the roasting procedure a t 400" C. Such a garnet suspected to contain 2% of wolframite was obtained through the cooperation of the Wah Chang Smelting and Refining Co., Glen Cove, X. Y., from the weakly magnetic fraction of a high-grade scheelite concentrate (73oJ, tungst,ic oxide) which was passed through a laboratory magnetic separator. Part, of the iron [1.42y0 iron(II)] was found to be in the ferrous state using the hl-drofluoricsulfuric acid-permanganate titration method (4). Hoviever, after roast'ing, t'he iron(I1) content dropped to 0.38% using the
Experimental. One-gram samples of wolframite concentrates were heated for three 1-hour periods (with intermittent filtration) with 50-ml. portions of 2% acetic acid containing 100 mg. of oxalic acid. The filtrates, after addition of sulfuric acid, were evaporated separately by fuming and the manganese was determined by using the silver nitrate-ammonium persulfate method ( 2 ) . The data (see Table 111) indicate that the solubility of manganese of wolframite in the medium chosen amounts to about 0.4 mg. per 50 ml., and, t h a t none of the wolframites tested contained more than 3% of the manganese in a nonhubnerite form. Since scheelite rarely contains more than 0.20% of manganese, the assumption is that all the manganese round exists in this mineral as hubnerite. REFERENCES (1) Dome, J. D., and Dana, E. S.,"The System of Mineralogy," T'ol. 11, pp. 1064-8, Wiley, New York, 1951. (2) General Servires Administration, U. S.Government Specification P-57R, S o . 53-8482 (1953). (3) Hillebrand, W. F., Lundell, G. E. F., Bright, €1. A.. and Hoffman, J. I., "Applied Inorganic Analysis," 2nd ed., pp. 446-9, Wiley, Kew York, 1953. (4) Ibid., pp. 912-20. (5) Li, K. C., and Wang, C. Y.. "Tungsten," A.C.S. Monograph No. 94, pp. 284.-95, Reinhold. Sew York. 1947. (6) "Scott', Standard Methods of Cheniical Analysis" (W. H. Furman, editor), pp. 561-2, \-an Kostrand, Xew York, 1939. RECEIVED for rei.ier September 21, 1 9 . X
Arceyteri l i a y 17, 1955.
Use of ~-(4=Ritrobenzyl)pyridine as Analytical Reagent for Ethylenimines and Alkylating Agents JOSEPH EPSTEIN, ROBERT W. ROSENTHAL, and RICHARD 1. ESS Sanitary Chemistry Branch, Chemical Corps M e d i c a l Laboratories, A r m y Chemical Center,
Procedures are described for colorimetrically estimating very low concentrations of ethylenimine and substituted ethylenimines in water and various alkylating materials in a nonaqueous solvent by the reaction of these compounds with y-(4-nitrobenzyl)pyridine followed by alkalinization. The procedure for ethylenimine and substituted ethylenimines is adaptable to routine analysis. Concentrations of ethylamine and ethanolamine (the hydrolysis product of ethy-lenimine) as much as 1000 times that of the ethylenimine do not interfere in the determination. Concentrations of the imines from 0 to 5 p.p.m. produce intensities in color in this reaction which adhere to the Beer-Bouguer law. In nonaqueous medium, the procedure has been applied to a-halogenated esters, diethyl sulfate, alkyl iodides, bromides, and chlorides; and various organic arsenic, phosphorus, silicon, and nitrogen chlorides. The procedure in nonaqueous solvents is recommended for estimation of reactive alkylating materials in the presence oE nonreactive alkylating material, but not vice versa. Development of optimum reaction conditions for individual compounds is recommended.
Md.
OESIGS a n d others ( 8 ) , reported that -y-(4-nitrobenzyl) pyridine, as well as 2- and +benzylpyridine, reacted with methyl iodide to form a salt which yielded a blue dye when treated with potassium hydroxide solution. The dye was assigned the following structure:
-
I \ l e -- S ~ = C H ~ N O I The application of this reaction to the detection of mustard gas \vas first discovered by Brown ( 3 ) . Gehauf ( 5 ) and Braun ( 1 ) utilized the general reaction to detect n number of organic alkylating compounds. The vapors of alkyl halides were adsorbed on silica gel impregnated with y-(4-nitrobenzyl)pyridine. Addition of alkali produced colors varying from blue to violet to brown. The group of compounds detected in this manner included a variety of examples such as diethyl sulfate, butyl thiocyanate, benzene sulfonyl chloride, diphenylchloroarsine, and diethyl phosphorofluoridate. Yo attempt was made to develop a procedure for quantitative estimation of the reacting compounds, or to determine the limits of sensitivity of the test. Swift and others (11)evpanded the qualitative studies of Gehauf and Braun
