Determination of Small Quantities of Molybdenum in Tungsten

Determination of Small Quantities of Molybdenum in Tungsten. Walker J. King. Ind. Eng. Chem. ... Loren C. Hurd and Fred Reynolds. Industrial & Enginee...
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350

INDUSTRIAL A N D ENGIiNEERING CHEMISTRY

Vol. 15, No. 4

Determination of Small Quantities of Molybdenum in Tungsten' By Walker J. King NATIONAL LAMPW O R K S O F THE GENERALEGECTRIC CO., NBLAPARK, CLEVELAND, OHIO

H E presence of works on 'tungsten and In this article the discoloring eflect of molybdenum in tungsten molybdenum recognizedthe small quantities of m o l y b b enurn in filament wire is discussed. The limitations of gravimetric methods distribution of lnolybdenum tungsten is important when for small quantities of molybdenum are explained. A new method in tungsten ores, and have the latter is .used in filafor the separation and colorimetric estimation of small quantities of developed methods for separating traces o f molybmerit wire for incandescent molybdenum in tungsten is described. The present method utilizes lamps. Tungsten filament the Property of reduced molybdenum to form a blood-red compound denum from tungsten with of molybdenum su[focyanate with a sulfocyanate salt. Ether is the object of obtaining a wire made from purified oxide usually conused as a medium jor extracting the molybdenum sulfocyanate and suitable materialforatomictains about o.ol to 0.05 colorimetrically estimating the quantity present. A special colorimweigh determinations. per e n molybdenum, eter. a modification of the Campbell and Hurlcy colorimeter, has The purpose of the analytbeen developed for use with the more volatile ether solution. The ical work in this paper was With increasingcontaminamethod has the following adoantaw: (a>None of the elements to fix the allowable limits tion of tungstenby molybusually associated with tungsten ores interfere with the method. of molybdenum contami5 cent denum above o , ~ per there is a greater tendency (b) The method is adaptable to the detection and accurate determinanation of tungsten filament tion of very small amounts of molybdenum. (c> The time required wire by the accurateanof the latter to evaporate for a single determination is less than two hours, or less than onefrom the hot filament and alysis of small quantities of fourth the time of the usual gravimetric processes. molybdenum in the presdeposit as a dark discolorA special procedure for analyzing tungsten which is very low in ence of large amounts of ation upon the walls of the bulb, thereby lowering the molybdenum is described. Limitations of the colorimetric method tungsten, operating efficiency of the are presented. lamp. Most metals or comGRAVIMETRIC METHODS pounds having higher vapor pressures than tungsten evaporate After an examination of available methods for the determiwhen present in the hot filament, but only the metals are nation of traces of molybdenum in tungsten, the method of likely to cause objectionable discoloration. When the quan- Rose as described by Melior3 was adopted. Rose's method tities of impurities are below definite limits, undesirable de- consists in treating the alkali salts of the two elements with position may be largely prevented. In the vacuum type of an excess of sulfuric acid and considerable tartaric acid, lamp chemicals are introduced in such a form that they saturating with hydrogen sulfide in a pressure flask, filtering combine with the metallic vapors to form colorless compounds the MOSS,igniting, and weighing as MOOa. After making or in some manner prevent discoloration, while in the gas- some preliminary experiments with Rose's method, Mr. filled lamp the shape of the bulb is designed to localize the Smoot, of Ledoux and Co., New York, gave the laboratory a deposit in the neck. procedure for improving Rose's method. In the modified The metals reducible by hydrogen contaminating crude procedure molybdenum was precipitated by a rapid stream tungstic acid, such as iron, copper, and tin, along with the of hydrogen sulfide at a temperature of 85" to 90" C. withoxides or salts of manganese, calcium, silicon, aluminium, out pressure in the presence of ferric salts to prevent the red tantalum, columbium, and the alkali metals, may be separated duction of molybdenum. The MoSa was immediately filfrom tungsten by rather simple chemical purification processes tered on asbestos, the filtrate treated with hydrogen sulfide, or reduced to such small limits that no harm will be done. the precipitate filtered and united to the first precipitate, In addition to chemical purification, tungsten is purified and the two dissolved directly with sodium peroxide and after reduction by heat treatment at high temperatures, water. In order to separate completely the tungsten conabout 150' to 200" C. below the melting point of pure tung- taminating the molybdenum the entire process detailed sten. Most impurities left in tungsten at this point, metals above was repeated, the sulfide precipitates dissolved as before and nonmetals alike, are volatilized in the order of their and the molybdenum determined as PbMo04 according to vapor pressures, those possessing the lowest vapor pressures, I b b ~ t e o n . ~ This method with certain changes was used for such as molybdenumlj* and thorium dioxide, volatilize so a large number of determinations until replaced by the slowly that the quantities removed by the process are colorimetric method. negligible. The changes referred to are as follows: (1) increasing the Experience has shown that crude tungstic acid made from size of the sample from 3-5 g. to 10-20 g.; (2) igniting the ores and concentrates containing 0.01 per cent molybdenum Moss and weighing as Moo3 instead of PbMoOd; (3) fusing or over when purified will contain a considerable portion of the weighed Moo3with sodium hydroxide, treating the fusion the molybdenum originally present. This fact coupled with with water and filtering off the insoluble residue; (4) reour present knowledge that all tungsten ores contain molyb- precipitating the molybdenum in a small volume as MOSSby denum would furnish strong evidence that no filament wire the same procedure given above, and finally igniting and is entirely free from it. From the results of over three hun- weighing as Moo3. The two weighings were regarded as dred analyses of tungsten concentrates, powders, and wire, separate determinations and are designated in this article made by the writer, it was found that no material except as Methods A and R, respectively. The caustic fusion special, purified oxide contained less than 0.01 per cent eliminated many impurities contaminating the first Moos molybdenum. Smith and his co-workers2 in their numerous residue and gave the most concordant results among the gravimetric methods mentioned. The method was accurate 1 Received September 8, 1922. * Numbers in the text refer t o the bibliography at the end of the article. within 0.01 per cent when the quantity Of molybdenum was

T

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within the limits 0.03 and 0.1 per cent, but wholly unreliable Other details necessary for trustworthy results are covered with amounts less than 0.02 per cent. This is shown by elsewhere in this article. The colorimetric apparatus and referring to the gravimetric analyses (Table I) of tungstic shaking flask, with accompanying sketches, are described oxide, Samples C and D given under Method B. Sample C below and are followed by a description of the present method prepared by the method of Smith and Exner was excep- of analysis. tionally pure. Sample D was low in molybdenum since it APPARATU s was obtained from the recovered tungstic acid of the molybCOLORIMETER-The special colorimeter which was used in denum sulfide precipitate, from which the original starting material analyzed less than 0.03 per cent. Both samples all colorimetric analysis is shown in Fig. 1. It is essentially the type described by Campbell and Hurley,g in which one-half of a analyzed a higher per cent of molybdenum than their method circular field of light from a standard solution is observed in of preparation warranted or their behavior during analysis juxtaposition with the opposite half of the image of the field of indicated. All previous samples of tungsten gave rather light from an unknown solution, whose color is to be matched. bulky sulfide precipitates and a characteristic blue color of The present apparatus is larger than the Campbell and Hurley apparatus and has certain additions which permit easier manipureduced molybdenum during the hydrogen sulfide treatment lation and greater flexibility. readily destroyed by ferric salts. Samples C and D gave ?mall sulfide precipitates and no blue color. Further exCOLOR /METER periments were made upon the weighed MoOa residues of both samples by treating with hydrochloric acid gas a t 250' -_..... \ .............................. C. according to Pechard.5 Sample D gave no appreciable .6 j..&qd " loss while C gave a loss less than one-half the original weight. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i. L eJ * 11' i i I ! ' / The volatilization tests showed conclusively that the MOOS contained impurities other than molybdenum and that the correct amount of molybdenum was far less than the weighed residue indicated. With the limitations of the gravimetric methods fixed it was evident that a colorimetric method might be used advantageously to give the required sensitivity. MOLYBDEPUXJJI SULFOCYANATE COLORTEST The sensitive blood-red color of molybdenum sulfocyanate has long been used as a delicate test for molybdenum. A. D. Braun,6 the originator of the test, employed zinc in hydrochloric acid solution t o reduce the molybdenum, and concentrated the molybdenum sulfocyanate by shaking out with ether. The exact composition of molybdenum sulfocyanate has not been established with certainty. Mass and Sand7 and their contemporary workers, Roenheim and Garfunkel,8 have macle extensive studies of this related class of compounds. The valuc of the sulfocyanate color test for the estimation of small quantities of molybdenum was suggested to the writer by L. Leley of the Philips' Lamp Works, Holland. Leley's method required that a solution of the alkali salts of tungsten and molybdenum be treated with an excess of hydrochloric acid in the presence of tartaric acid, the solution treated with sulfocyanate salt, the molybdic acid reduced with stannous chloride, and the red color Fro. 1 shaken out with ether. Without transferring, the colored ethereal solution is matched against molybdenum standards The colorimeter tubes A and B n-ith attached reservoir, e, are prepared in like manner, due attention being paid to main- made of Pyrex glass. They have an approximate capacity of 250 cc., an inside diameter of 4 cm., and an approximate height taining equal volumes of the solutions.

................................. :I! J+ 1...,111.......11)1....1I......I.lI

',"la

i

ESSENTIAL POINTS OF

THE

NEWMETHOD

With the essential principles of Leley's method in mind, modifications were made in the new method which allow greater flexibility and refinement than is possible in the original method. The important features of the new method are as follows: 1-Accurately matching the color of the ethereal solution containing the extracted molybdenum, against a similar solution containing the standard by means of a special colorimeter. 2-Regulating the size of the sample to obtain the proper quantity of color. 3-Employing a shaking flask with siphon for shaking out with ether and transferring the ethereal solution to the colorimeter. 44tandardizing the source of light for the colorimeter with a 500-watt "Trutint" daylight unit. &-Fx in ig the concentrations of the constituents in the solution containing the sample within the limits obtainable through the accurate and systematic addition of the reagents and the maintenance of uniform conditions.

of 23 cm. The bottoms of the tubes are clear glass made by sealing pieces of large flasks on the bottoms, which have been previously ground to a plane. The tops of the tubes are ground level so that the plate-glass covers fit snugly over the tops. Tube B is calibrated to contain 250 cc. and marked on side-arm a. A separate scale equal to the length of side-arm a to mark, and graduated in 100 equal divisions, is fastened behind a. The use of a separate scale with a white background and black markings facilitates rapid and accurate readings. The length of the side-arm of the tube A is equal to the length of side-arm of tube B. Side-arm a is divided into 10 equal divisions and etched on the glass. Fractional readings of the large divisions are made with a movable glass sleeve fitted with a paper scale equal to the length of a large division and subdivided into 10 equal divisions. This device saves extra calibrating and provides accurate readings from 1 to 100. No correction for the taper of the tube is necessary if the diameters of the tubes are reasonably uniform and the inside diameters of their opposite ends do not vary more than 0.4 mm. The correction for the difference in the volumes of the tubes is equal to volume of tube A (to mark) divided by volume of tube B (to mark). The volume of reservoir e (to mark) is equal to the volume of tube B and side-arm to calibrated mark. Trapf prevents the loss of ether solution while mixing the standard.

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The cabinet C is a dustproof box inclosing two mirrors and telescope. The mirrors are supported with a mechanical device t o give three adjustments: (1) rotary movement, ( 2 ) sliding movement parallel to axis, (3) displacement movement relative t o the position of the telescope and the direction of the light from the tubes. Glass plates covering the openings in the bqttom of the box transmit light from tubes A and B to the mlrrors. The tube B is 20 cm. long, 1.2 cm. in diameter, and is lined with black velvet t o prevent disturbing reflections. The pinhole aperture d in the removable eyepiece c is 1 mm. in diameter while the opening g in the opposite end of the telescope is 4 mm. An eyeshade, f , is attached t o the end of the telescope, which cuts off light from the outside and permits the observer t o keep the left eye open while making observations. The height of the standard solution in B is controlled by a pressure regulator, D. The pressure bottle a has a capacity of 500 cc. and is half filled with water saturated with ether. By turning the pulley c the height of the leveling flask b regulates the amount of water and air in a, which automatically provides pressure regulation for the tube B. The purpose of introducing a is to prevent the evaporation of ether from the reservoir e . The pulley c has a friction spring, d, which fixes the height of b a t any desired level. The mirror E is swung in position t o reflect the light from the white plate-glass reflector in the rear of the colorimeter up through the tubes A and B into the openings at the bottom of cabinet C. SHAKING FLASK AND SIPHON-The shaking flask consists of a 300-cc. flask sealed to a 400-cc. short-neck (3 cm.) flask and shaped at the mouth t o fit asmall rubber stopper. A small opening is made near the mouth t o admit air. After shaking out a solution the ethereal layer is removed by properly adjusting the 3-mm. capillary siphon, inserting the rubber stopper, and forcing air through the opening until all the ether is forced out. ILLUMINATING EQUIPMENT-A

500-

watt “Trutint,” north skylight unitlo provided the source of light both for the extraction process and color matching. This type of lighting unit is equipped with a blue-glass color filter and is designed to give a quality of light closely approaching north skylight. A dependable source of light, reasonably uniform both in quality and quantity and reproducible at will, made possible accurate color observations at all times, a condition which was not possible with daylight. To PIG.2-SHAKINGFLASK obtain the best conditions of light diffusion, the glass filter was sand-blasted WITH SIPHON and the diffused light reflected directly into the colorimeter by a polished plate of white glass. REAGENTS SODIUM HYDROXIDE SOLUTION-A solution of NaOH is prepared by dissolving 20 g. C. P. NaOH (electrolytic) in 600 cc. of distilled water, diluting t o 1 liter, and allowing t o stand until the iron precipitate settles. TARTARIC ACID SOLUTION-This solution is made by dissolving 600 g. c. P. tartaric acid in 700 cc. of boiling water, cooling, and diluting t o 1 liter. STANNOUS CHLORIDESoLuTIoN-Freshly prepared C. P. SnClz is used. It is prepared by dissolving 150 g. SnC12.2Hz0 in 100 cc. concentrated HC1 and 250 cc. distilled water. Solution should be clear when prepared, and protected from oxidation. ETHER-The

ether used for the extraction should be tested

with potassium iodide and starch. If a blue color develops, the ether should be shaken with a 10 per cent solution of sodium thiosulfate and redistilled. A blank test should give no color after several hours’ standing. The precaution of redistilling has never been found necessary. STANDARD SODIUMMOLYBDATE SoLuTIoN-Pure molybdic trioxide is prepared by igniting C. P. (NH&Mo04 to MooI and resubliming in silica or platinum dishes. The sublimed oxide is dissolved in a small excess of a 10 per cent NaOH solution, neutralized with dilute HC13 and then made alkaline t o litmus. The solution above is diluted to approximately 0.1 N , after which the molybdenum is accurately determined by precipitating and weighing as PbMoO4. A portion of this solution is diluted so that 1 cc. will contain 0.05 mg. molybdenum.

Vol. 15, No. 4

METHODOF ANALYSIS The colorimetric method of analysis has given satisfactory results on a variety of samples, and it is believed that with reasonable care the method as outlined will give reprducible results. SOLUTION OF 8AbfPLE-Tungsten and molybdenum must be in the form of their alkali salts. Tungsten metal is oxidized in the wet way. Weigh 4 g. of metal into a 200-cc. platinum dish, cover with 30 to 40 cc. of hydrofluoric acid, and add drop by drop concentrated or dilute nitric acid, as the violence of the reaction indicates, until the tungsten is dissolved. Evaporate the solution nearly to dryness, add concentrated nitric acid, and evaporate to dryness. Repeat acid treatment three times, evaporating to dryness each time. Ignite at a low temperature not to exceed 550” C. Ignition of all tungsten samples is necessary to eliminate organic matter and to break up the tungstic acid hydrates and complexes. Tungstic acid is treated three times with concentrated nitric acid, evaporated to dryness, and ignited. Tungstates soluble in caustic are treated directly. Boil ti 5-g. sample, after treatment as directed above, with 25 cc. sodium hydroxide solution (35 cc. for sample over 12 g.) until solution is complete. T o the solution add 75 cc. hot water and boil. No appreciable residue of tungsten should remain. Fusion of sample of tungstic oxide with sodium and potassium carbonates is apt ill be shown by to cause a slight loss of molybdenum. This w referring to the analyses of Samples A and B (Table I). Filter the solution in a Gooch crucible on an asbestos mat, wash with 5 per cent sodium chloride solution, and transfer to a 250-cc. calibrated flask and dilute t o mark. PRELIMINARY TREATMEN‘ILTransfer a 75-CC. aliquot to a 500-cc. Erlenmeyer flask, and neutralize with dilute hydrochloric acid (1:lO) using neutral litmus paper. At no time should a precipitate of tungstic acid be allowed to form. When the solution is slightly acid immediately add tartaric acid solution proportionate to the amount of tungsten present, using 20 cc. of solution for every 6 g. of WOs or fraction. Transfer to a 400-cc. shaking flask, add 25 cc. dilute hydrochloric acid (1:5) and 5 cc. of a 30 per cent potassium sulfocyanate solution, and dilute to approximately 350 cc. Cool to 5 ” or 10” C. EXTRACTION WITH ETHER-TOthe cooled solution add 20 cc. of stannous chloride solution. Thorough mixing is best done by blowing forcibly into the pipet and directing the emerging stream into the solution. Immediately add 90 cc. ether and sufficient water to bring the water meniscus up to the bottom of the constriction when the two layers are saturated with each other. Insert a cork in the flask, hold the finger over the small opening a t the top, and shake the flask vigorously one-half minute. Cool the flask in ice water until the ether layer separates. Adjust the siphon and transfer the ether to color tube A. Add a 50-cc. portion of ether to the shaking flask, and repeat the extraction as long as any color is removed. When aqueous solutions turn slightly blue after the addition of stannous chloride some of the molybdenum stays in a form which cannot be shaken out. I n some cases over 20 per cent of the molybdenum remains undetected. This is probably due to the formation of hydrated or complex compounds of tungsten when precipitated metatungstic acid or insoluble residues are redissolved. The resolution of the fine precipitate by the addition of tartaric acid is not sufficient to prevent the formation of the blue color. I n several cases a poor quality of tartaric acid has been known t o cause a blue color, but this can be detected by a blank test. When an appreciable quantity of blue

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color has formed it has been considered a safer plan to disANALYSIS O F TUNGSTEN WITH 5 P. P. M. AhfOLYBDENUhf-In card the determination and start a new one. an attempt to make an accurate analysis of Sample E (Table STAXDARD ETHERSoLuTIoN-standard ether solution is I), which was believed to contain a very small quantity of prepared by adding molybdenum to specially purified tung- molybdenum, the following scheme was adopted: A 16.5-g. sten and shaking out in the regular way. A suitable quality sample of E was carried through the regular procedure and of purified tungsten very low in molybdenum may be ob- the ether extractions transferred to tube A. Another 16.5-g. tained by recovering and purifying the tungstic acid from the sample of E was treated in like manner, except that 0.25 mg. aqueous solutions of the ether extraction. Purification is of molybdenum was added to the sample a t the beginning of best made by ammonium paratungstate precipitation fol- the procedure and the ethereal solution used as a standard. lowed by nitric acid digestion. Sample E (Table I) was pre- The amount of molybdenum in milligrams is determined as pared in this manner. Weigh 3 g. of ignited oxide into a follows: 500-cc. flask, add 10 cc. of a standard molybdenum solution, LetX = MoinA equivalent to 0.5 mg. molybdenum and follow the procedure a = Mo added to B (standard) to the extraction with ether. After shaking the solution out X a = Total Mo in B filled to mark b = Total height of B filled to mark with ether, transfer the ether solution to tube B and continue c = Height of B when matched t o A extracting with 50-cc. portions until the reservoir e is filled to c = Fractional height when B matches A mark. Mix the standard by blowing air through the reservoir replacing the evaporated ether if necessary, using only the x = ( X + a ) x 2b ether which has been shaken out. The volume of the reservoir e filled to mark is equal to 100 scale divisions. Loss of nc X = -= mg. Mo in A when a is in mg. ether is largely prevented by covering the tops of the color b - G tubes. The calculation for Determination 1, Sample E, is: MATCHING OF CoLoRs-The standard solution in tube 13 26 0‘25 mg‘ = mg. Mo in Sample E = 0.087 mg. MoinA = is matched against the unknown qolution in tube A. To ac100-26 complish this, disconnect the rubber tubing from the trap f, fill the reservoir e to the mark, and lower the leveling reservoir 016.5 .087 X 1000 = 5.3 p. p. m. molybdenum b until the pressure bottle a is empty. Connect the rubber tubing again to the trap f. With the light properly adjusted Determination 2 was a duplication of 1. Determination 3 behind the colorimeter, the mirror E is turned so that uniform was made with a new standard and was made in the same illumination is provided in both tubes. Manipulate pulley manner. Determination 4 was made with 0.5 mg. molybso that the height of the solution in B is regulated to give denum in the standard. equal color densities in both tubes, and note reading on the scale. With a little practice readings can be duplicated within one or two scale divisions. If the color reading is over 90 divisions, fill A to a convenient mark, mix and drain off sufficient ether to permit the readings to fall between 70 and 90 scale divisions. The volume of the ether aliquot may be accurately measured by using the calibrated sleeve described under “Colorimeter.” When it is necessary to remove more than half of the ether aliquot, a second but smaller sample is taken and sufficient purified tungstic acid, from which the standard was prepared, added to make a total of L.5 to 3 g. of WO,. If the color reading is less than 50 divisions a proportionally larger sample is taken so that an approximate reading of 75 divisions is obtained. However, the quantity of tungstic acid used in making the standard need not be increased except where great refinement is desired. It will be seen by reference to Table I1 that the first determination containing no tungsten showed the largest Volume o f a p e o u s solufson ~ Z ~ I Qyo0 ~ S CC. error of the entire set of analyses. The next largest error is Fro.3--I$FFICKENCY OF! EXTRACTION OF MOLYBDENUM COLOR on the determination containing 4 g. of tungstic oxide. The per cent error on the total molybdenum added is less than 5, which can be classed within the limits of experimental In preparing a reliable procedure for colorimetric analysis errors. The results indicate that quantities of tungstic of molybdenum, the importance of adopting uniform condioxide between 1 and 12 g. would have little or no effect upon tions cannot be too strongly emphasized. This applies esthe quantity of molybdenum extracted. pecially to the quality of reagents and the conditions effectCALCULATION OF MoLYBDEwM-The quantity of molyb- ing their concentration. New reagents should be tested by running blank determinations. After the addition of the denum in parts per million is as follows: sulfocyanate an analysis should be carried through promptly. Mg. of Mo X factor A X factor B X color reading X Turbidity or precipitation occurring in either solution pre10 vents the complete extraction of molybdenum, or makes G. sample X aliquot taken accurate color matching impossible. Although standard =P. p. m. Mo solutions have stood over a week without measurable deterioration, it is probably better to prepare a fresh solution Mg. Mo in standard = Mg. Mo added plus Mo in sample each day and check against a standard sample of tungstic Area of cross section of tube A acid. The stability of the solutions is probably due to the Factor A = Area of cross section of tube B reducing action of stannous chloride held in solution by Divisions read in tube A before taking aliquot Factor B = ether.ll Divisions read in tube A after taking aliquot

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INDUSTRIAL A N D ENGINEERING CHEMISTRY

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-

F

Sample A. ........

B

.........

Detn. No.

G. WOs 1.2 1.5 1.4 1.4 1.4 1.3

1

2 3 4 5 6

Average

D

.........

Ea. .......

a b

1 2 3

1.2 9.0 7.2 Average

1 2

1.4 8.3 Average

1 2 3 4

TABLEI-COMPARATIVEANALYSES OF Mo IN SAMPLES OF WOa GRAVIMETRIC -COLORIMETRIC--------, 7 Color Mo Found G. Method A Method B Reading Mg. P . p . m. wo3 Mg. P. p. m. Mg. P . P. m. 310 9.2 5.00 540 2.80 305 295 9.2 6.10 660 2.70 295 4.35 475 2.80 305 330 9.2 340 9.2 3.70 400 3.70 400 4.35 475 2.30 250 330 9.2 320 9.2 4.15 450 2.70 295 321 9.2 4.61 500 2 84 m..x_ ._ 43 0.220 147 9.2 3.25 355 1.80 195 79 0,400 160 9.2 3.00 325 1.50 165 142 18.4 83 0.425“ 7.40 400 3.80 205 76 0.390 150 18.4 8.70 47 5 4.60 250 155 18.4 85 0.435 5.25 285 3.00 165 151 368 195 12 0.061 51 8 2.60 325 1.00 125 79 0.400 44 . 8 4.50 560 1.40 175 48 68 0.345 48 3.55 443 1.20 150 8 0.041 29.3 9.2 3.30 360 1.30 140 48 0,244 29.6 18.4 4.70 255 1.85 100 29.5 308 120 26 0.088 5.3 24 0,079 Gravimetric separation with hydrogen sulfide made. No in4.8 } 6.3 30 0.107 dication of the presence of Mo 5.7 I 16.5 0.097 5.5 ~

1.5 2.5 3.0 2.6 2.8

1 2 3 4 5 Average

c.....

Vol. 15, No. 4

16.5 16.5 17.0 17.0

Average Slight loss from NanCOs-KCOn fusion. Formula used to calculate per cent Mo.

INTERFERING ELEMENTS Kone of the elements commonly associated with tungsten ores interfere with the molybdenum determination. The following elements were found not to interfere: iron, copper, manganese, nickel, cobalt, titanium, columbium, tantalum, uranium, chromium, vanadium, thorium, aluminium, phosphorus, calcium, arsenic, and silicon. Separate tests were made by adding a solution containing the element to a blank determination and to a regular tungsten determination, and completing the analysis according to the standard procedure. The blank determinations in every case were colorless, while the molybdenum analyses on the regular samples were unchanged.

An analysis containing no tungsten (Table 11) analyzed approximately 85 per cent of the total molybdenum added, while the samples in the remainder of the series of analyses containing varying amounts of tungstic oxide from 1 to 12 g. analyze in every case over 95 per cent of the total molybdenum added. A comparison of the gravimetric and colorimetric analyses (Table I) shows that the gravimetric method is unreliable for quantities of molybdenum in tungsten less than 300 p. p. m., while the colorimetric method is trustworthy for quantities of molybdenum as low as 10 p. p. m. TABLE111-DETERMINATIONOF VARIABLEQUANTITIESOF M o AnalyAMOUNTS OF WOaa

IN

EQUAL

Color Mo Found Mo Added Error-Mo Present Reading Mg. P.p.m. Mg P.p. m. Mg. P. p. m. 2*1 0.010*5 10*5 0.008 14.2 0.072 51 0.058 41 6 jlb:6ib +ib 26.5 0.134 96 0.108 77 +0.026 +19 37.5 0.190 136 0.158 113 +0.032 +23 46.5 0.236 168 0.208 148 +0.028 $20 53.1 0.270 193 0.258 184 +0.012 $9 62 7 0.322 230 0.308 220 $0.014 +10 70.8 0.360 257 0.358 256 +0.002 $ 1 77.1 0.392 280 0.408 291 -0.016 -11 86.3 0,439 314 0.458 327 -0.019 -13 -=was Sample E (5 P. p. m.). Sample taken equals 1.4 g. wos. 100 divisions of scale 30.508 mg. Mo. NOTE: Readings corrected for volume change of standard. 81s

EFFICIENCY OF EXTRACTING THE MOLYBDEXUM SULFOCYANATE The efficiency of extracting molybdenum sulfocyanate is represented in Fig. 3. Five 50-cc. ether extractions were made upon 10 samples, a color reading being taken after each extraction. At the end of the fifth extraction, when the ethereal solution had become colorless a final color reading was taken and regarded as 100 per cent extraction. The efficiency is equal to the reading taken a t the end of each extraction divided by the final reading taken a t the end of the fifth extraction. The average efficiencies of the 10 samples for 4 extractions are as follows: Extraction Average per cent efficiency Color

1 85.7 Ver). strong

2

3

95.4 Light

98.4 Very light

4

5

99.7. 100.0 Doubtful None

LIMITATIONS OF METHOD An examination of the colorimetric analyses of Samples -4,B, C, and D (Table I), containing 321, 151, 48, and 29 p. p. m. molybdenum, respectively, shows that the variation between the maximum and minimum value for each sample is less than 10 per cent of the total molybdenum present. TABLE11-DETERMINATION OF M:O WITH VARIABLE QUANTITIES OF W O p G. Wos Color Mo Found Mo Added Error-Mo Present Taken Reading Mg. P.p. m. Mg. P. p. m. Mg. P.P. m. None 64 0.325 , 0.375 -0.050 1 74 0.376 374 0.380 380 -0.004 -6 2 75 0.381 190 0.385 193 -0.004 -3 3 77 0.391 130 +0.001 0 0.390 130 0.406 101 4 80 +0.011 t-2 0.895 99 0.382 76 5 75 0.400 80 -0.018 -4 0.406 58 7 80 -1 0.410 59 -0.004 0.406 45 9 80 -0.014 -2 0.420 47 0.435 36‘ 12 85 0.431 36 -0.004 0 0 WOa Sample E (5 p. p. m. Mo). 100 divisions of sc,ale = 0.508 mg. Mo.

..

...

...

No. 1 2 3 4 5 6 7 8 9 10

Errors of color matching are reduced to a minimum by adjusting bhe size of the sample so that B scale reading of 60 to 90 divisions is obtained. By referring to the analyses in Table 111, it will be seen that the effect of low readings on the scale is to give high results. ACKNOWLEDGMENT The writer wishes to thank Mr. J. G. Wild, manager of the chemical laboratory, for assistance in the work, and also Mr. A. C. Norris for the drawings.

BIBLIOGRAPHY 1-Langmuir and Makay, Phys. Rev., 4 (1914), 377. %Smith and Exner, Proc. Am. Phil.SOL,43 (1904), 123; Marbaker, J . Am. Chem. Soc., 87 (1915), 86. 3--Mellor, “Quantitative Inorganic Analysis;’ 1913, p. 417. 4--Ibbotson, “The Chemical Analysis of Steel Works Materials,” 1920, p. 140. 5--Pechard, Com$l. rend., 114 (1891). 173. 6--Braun, 2.anal. Chem., 6 (1867), 86. 7-Mass and Sand, Ber., 4 1 (1908), 3367. 8-Roenheim and Garfunkel, Bn., 4 1 (1908), 2386. 9-Campbell and Hurley, J. Am. Chem. Soc., 88 (1911), 1112. 10-Supplied by Nela Specialties Division, Nela Park, Cleveland. 11-Seidell, “Solubilities of Inorganic and Organic Substances,” 1911, p. 140.