Determination of Minute Amounts of Lead in Biological Materials A Titrimetric-Extraction Method E. S. WILKINS, JR., C. E. WILLOUGHBY, E. 0.KRAEMER, AND F. L. SMITH,~ N D Tumor Clinic of Jefferson Hospital, Philadelphia, Pa.
I
A method sensitive to 0.001 mg, is describedfor destruction of organic m a t t e r the determination of minute amounts of lead in and for the preparation of the investigation concerning the efficacy of various colloidal digestion residue for dithizone biological materials. Dithizone (diphenylthioextraction. lead preparations for the treatcarbazone) is employed first in the separation of ment of certain diseases, a proPROCEDURE cedure for the quantitative dethe lead f r o m other metals, and secondly in the final estimation of the lead by means of a quantiGLASSWARE AND REAGENTS. termination of minute amounts of lead in blood, excreta, tissues, Bismuth is the only Pyrex glassware should be used tative titrimetric etc., was required. A review of wherever possible. Consistent interfering element likely to be encountered. A the literature i n d i c a t e d t h e results cannot be obtained with series of lo-to 15-gram necessity for a method sensitive Of whole blood ordinary resistance-glass digescan be analyzed with a n average time per sample tion flasks or separatorv funnels. to 0.001 mg. of lead. Of the numerous methods p r o p o s e d , The separatory funneis should of aboul2 hours. those considered most promising preferably be of t h e S q u i b b were s t u d i e d principally with type. It is absolutely necessary respect to lead recovery and to the sensitivity of the final that each piece of glassware used be scrupulously clean. Imreaction by means of which lead estimation is made. mediately before use, the article, previously cleaned by conThe radio-indicator technic (I$),with either radium-D or ventional methods, is further cleaned with a mixture of a thorium-B, was employed for the purpose of ascertaining lead dilute solution of potassium cyanide and dithizone solution losses. Despite numerous refinements in technic, chromate No. 2. If the piece of equipment shows a negative lead methods (7, 11, 1.4, 16), colorimetric lead sulfide methods (8, IO, test, it is again thoroughly rinsed with redistilled water and 18, 23), the turbidimetric metabisulfite procedure (4,6, 13 18), and electrolytic methods (3, 12, 16, 17, 20, 92, 94) were ah un- is then ready for use. The reagents should be as free from lead as possible, but satisfactory in the authors’ hands. The most promising line of attack was found to be the reaction between lead and dithieone it is not necessary to purify the best c. P. grades of these ma(diphenylthiocarbaeone), which has received considerable study, terials. Combined reagent blanks are carried along simulparticularly by Fischer and his co-workers (8, 9), either as a taneously with each analysis and the results are corrected means for reliminary lead separation, or for both this and subsequent leazestimation. Their investigations have served as the accordingly. The concentrations of ordinary reagents are basis for further work b others (1, 6, 19, 21, 26). Fischer and expressed on a volume per cent basis, referred to the usual comLeopoldi (9) state that &hieone may be used for the separation mercial concentration; thus, 5 per cent ammonium hydroxide of minute amounts of lead from relatively large quantities of aluminum, antimony, arsenic, beryllium, cadmium, copper, contains 5 ml. of ammonium hydroxide (sp. gr. 0.90) in 100 mercury, silver, and zinc. Bismuth, monovalent thallium, and ml. of solution. The special reagents required are as folstannous tin are interfering elements. The colorimetric pro- lows : cedure of Fischer and Leopoldi (9)was evaluated but was found unsatisfactory because of the large number of standards required 1. Citric acid solution, 4 per cent: 40 grams of the monoto cover a wide range of lead values, the instability of these hydrate and 1 gram of salicylic acid (as preservative) per liter of standards, and the nonreproducibility of color both in standards solution. and samples. 2. Sodium chloride-hydrochloric acid solution: 5 per cent hydrochloric acid saturated with sodium chloride at room temDuring this investigation it was observed that lead can be perature. quantitatively extracted with a dithizone solution without 3. Redistilled water. Water distilled from R large Barnstead using an appreciable amount of excess reagent. This ob- still is redistilled from alkaline permanganate solution in an allservation led to the development of what may be called a glass Pyrex still. This double-distilled water is used in all cases for preliminary rinsing in cleaning operations. titrimetric-extraction method for estimating lead. I n this except 4. Dithizone solution No. 1. Dithizone was obtained from method, initial lead separation is made with a chloroform solu- the British Drug Houses, Ltd., London, England. This material tion of dithizone, the lead is converted to the nitrate, and it is quite impure, but for the initial separation of lead it may be is then reextracted with the least possible amount of a used without purification. A solution is prepared for this purpose containing 0.04 gram of the impure dithieone per liter of chlorostandardized dithizone solution. A reagent blank is car- form. ried along simultaneously with the sample, and proper cor5. Dithiaone solution No. 2. The dithiaone used in the titrirection is made for lead added in this manner. The use of metric extraction must be purified. One-tenth gram of the comdithizone simplifies the analytical procedure by reducing the mercial material is dissolved in 30 ml. of chloroform in a large separatory funnel, and the solution is extracted once with 900 ml. number of steps involved, thereby minimizing the chances of 0.5 per cent ammonium hydroxide solution. After discarding for lead losses and lead contamination. the chloroform phase, the aqueous phase is neutralized t o litmus The method is described below in terms of the procedure with 10 per cent hydrochloric acid, and the purified dithiaone used for the analysis of 10- to 15-gram samples of whole blood. thus precipitated is extracted with chloroform. The chloroform solution is then diluted so as to be equivalent t o 0.01 mg. of lead It is also applicable in the analysis of tissue, bone, and excreta, per ml. (about 1400 ml., depending on the purity of the initial as well as larger amounts of blood, the only modification be- material). The solution is delivered to a Pyrex reservoir from ing that larger quantities of reagents are required for the which siphons lead to a series of burets. The stopcocks in the N CONNECTION with an
33
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 7, No. 1
delivery system and in the burets are lubricated with glycerol. A very small amount of Lubriseal is used a t the extreme ends of each stopcock. Both the supply reservoir and the burets are suitably protected against evaporation of chloroform and undue exposure to light.
SEPARATION OF LEAD. The separation of lead (and bismuth, if present) from other metals is effected by extraction of the sample, prepared as described above, with dithizone solution No. 1.
STANDARDIZATION. Dithizone solution No. 2 is standardized in the following manner:
In order to insure the complete removal of lead from the Kjeldahl flask, a drop of 10 per cent otassium cyanide solution, 0.5 mi. of water, and the first 5 ml. ofdithizone solution No. 1to be used in the extraction procedure, are added to the flask, vigorously shaken, and then quantitatively delivered, with thorough rinsing with water, to the 250-ml. separatory funnel containing the sample. The separatory funnel is shaken, and, depending upon the amount of lead present, the color of the chloroform layer ranges from a brilliant red-orange, with appreciable amounts of lead, through purple to the unchanged green color of the dithizone reagent solution. Extraction of the a ueous solution is repeated with successive 5-ml. portions of the dihzone solution, delivering each, after extraction, to a 125-ml. separatory funnel, until the color of a newly added portion of dithizone remains unchanged. The aqueous phase is extracted once more, as a precautionary measure, and is then discarded. The total volume of dithiaone solution used is noted as it gives a preliminary indication of the amount of lead present and is therefore of value as a guide in the final lead estimation. The chloroform solution of the lead-dithizone complex is first washed with 25 ml. of water containing one drop of 10 per cent potassium cyanide solution, quantitatively separated, and transerred to another 125-ml. separatory funnel. Contamination of either phase by the other is avoided by running out the chloroform layer until about 0.2 ml. remains. Small portions of chloroform are successively added and withdrawn, maintaining a chloroform trap a t all times, until the Separation of all chloroform-soluble components is complete. The lead is removed from the organic complex by shaking the chloroform solution with 10 ml. of 1 per cent nitric acid; the dithizone remains in the chloroform phase, whereas the lead, in the form of the nitrate, passes into the aqueous phase. After separation of the two phases, the lead nitrate solution is washed once with chloroform. The chloroform solution containing the bulk of the dithizone and the chloroform wash are combined and reextracted with a second 10-ml. portion of 1 per cent nitric acid. After separating and washing this aqueous phase as before, it is added to the first lead nitrate solution, and the combined solution is washed repeatedly with small portions of chloroform until a freshly added portion remains colorless. The lead nitrate solution is now ready to be prepared for the final titrimetric extraction. If the initial dithizone extraction indicated the presence of more than 0.2 mg. of lead, the sample is diluted to a known volume and an aliquot is taken for final analysis. Samples containing up to 0.50 mg. can be handled satisfactorily, in which case the extracting reagent is standardized against a corresponding known amount of lead. It is more convenient, however, to work with 0.20 mg. of lead or less. The sample is prepared for the final extraction by adding 2 ml. of 10 per cent potassium cyanide solution, 2 to 3 drops of phenol red, and then 5 per cent ammonium hydroxide dropwise until pH 7.5 is reached.
Five to 20 ml. of a standard solution of recrystallized lead nitrate containing 0.01 mg. of lead per ml. are delivered to a 125mi. separatory funnel. If less than 20 ml are taken, the volume is made up to 20 ml. with water. After the addition of 2 ml. of 10 per cent potassium cyanide solution and 2 to 3 drops of phenol red, the solution is adjusted to pH 7 5 with 5 per cent nitric acid. If 0.20 mg. of lead is taken for standardization, 10 ml. of the dithizone solution are delivered from a buret to the separatory funnel, which is then vigorously shaken. The green color of the reagent solution is immediately discharged with the simultaneous formation of the brilliant reddish orange colored lead-dithizone complex, which is soluble in the chloroform but practically insoluble in the aqueous phase. Shaking is continued until no further increase in the depth of color is produced, indicating that the reaction is substantially complete. A mechanical shaker greatly facilitates the work. After complete subsidence, the chloroform layer is discarded, 5 ml. of the dithizone solution are added to the separatory funnel, and the extraction procedure is repeated. (About 0.10 ml. of the chloroform phase is left in the beparatory funnel after each extraction to prevent any loss of the aqueous phase.) This is continued, using smaller and smaller quantities of the dithizone solution, and removing each chloroform extract before the next portion of dithizone is added. As the end point is approached, the dithizone reagent is added in 0.1-ml. and finally 0.05-ml. portions, a few drops of chloroform being added to give an adequate volume for judging the color produced. A stage is eventually reached where the green color of the added increment of reagent changes to a purple shade that persists after vigorous and prolonged agitation. The next 0.05-ml. addition of dithizone should remain practically unchanged in color. This green stage is taken as the end point, and the total volume of dithizone solution consumed up to that point is read from the buret. A blank determination, in which 20 ml. of water are used in place of the lead nitrate solution, is carried through in exactly the same way as the sample. After deduction of the blank correction, the lead equivalence of the reagent solution is calculated. Because of gradual deterioration, this solution must be standardized on each day analyses are made.
PREPARATION OF SAMPLE.The organic matter in 10 to 15 grams of whole blood is completely destroyed by wet oxidation in a Kjeldahl flask wherein 15 ml. of concentrated nitric acid (sp. gr. 1.42), 2 ml. of concentrated sulfuric acid (sp. gr. 1.84), and 2 ml. of perchloric acid (sp. gr. 1.54) are used, and are added in this order. After adding the nitric acid, the digest is concentrated to somewhat less than 5 ml. The sulfuric acid is then added and heating a t the same tem erature is continued until the nitrogen oxides have been com fetely driven off. Following this, the temperature is increases until sulfur trioxide fumes are evolved, and shortly afterwards the perchloric acid addition is made. The function of the perchloric acid is to oxidize rapidly and completely the remaining organic matter. This reagent is not dangerous to use for this purpose, provided it is added dropwise to the hot, fuming digestion residue. After the addition of the perchloric acid, the fuming off of sulfur trioxide is continued for about 5 minutes. The final volume is about 3 ml. Whereas the use of 0.05 gram of lead-free selenium as a catalyst is definitely advantageous in the di estion of 50 to 100 grams of whole blood, it does not noticeably sforten the time required for this operation in the case of 10- to 15-gram samples. To the cooled digest 5 ml. of water are added and the residue is dissolved by the addition of 5 ml. of the sodium chloride-hydro. chloric acid solution, with subsequent heating. The solution is then made just barely alkaline to litmus with ammonium hydroxide (sp. gr. 0.90), after which 5 ml. of 4 per cent citric acid Polution are added to dissolve the precipitated ferric hydroxide. Gentle heating is conducive to complete solution, which must be obtained at this stage. Two milliliters of 10 per cent potassium cyanide solution are added, followed by ammonium hydroxide (sp. gr. 0.90) until the solution is just alkaline to litmus, and then by 1 to 2 additional drops. The solution is now transferred from the Kjeldahl flask, with thorough rinsing with water, to a 260-ml.separatory funnel.
LEAD ESTIMATION BY TITRIMETRIC EXTRACTION. The titrimetric extraction of the lead is carried out with dithizone solution No. 2 in exactly the same manner as used for the standardization of this reagent. From 15 to 25 per cent of the total volume of dithizone estimated to be required is used in the first step of the extraction, which is then continued, using smaller and smaller portions of the dithizone solution, as previously described. Combined reagent blanks, consisting of the same amounts of all the reagents as used in the analysis, are carried along simultaneously with the sample and in identical apparatus. If the end point should be overstepped, a reextraction can be made, provided all the lead-dithizone extracts of the sample have been saved. The chloroform solution is extracted twice with 1 per cent nitric acid and the resulting lead nitrate solution is again prepared for titrimetric extraction in exactly the same manner as previously described. EXPERIMENTAL RESULTS The accuracy of the method is illustrated by the following representative results. The data in Table I were obtained
ANALYTICAL EDITION
January 15, 1935
35
In carrying through the titrimetric extraction, equilibrium in the distribution of lead between the aqueous and chloroform phases must be attained with each portion of dithizone solution before continuing to the next. Otherwise erroneous OF LEADIN THE ABSENCEOF OTHER results will be obtained, and near the end point a series of TdBLE I. DETERMINATION METALS pinkish purple shades will be obtained instead of the disLEADTAKEN LEADFOUND ERROR tinct and abrupt changes through the colors light pink, purple, Mg. Me. Me . and green, with the last three 0.05-ml. additions of dithiaone solution. Since dithizone is soluble in alkaline aqueous media, the p H of each solution just before titrimetric extraction must be carefully adjusted to the same value. Consistent results are obtainable by controlling the dithkone As Pb(N0s)i distribution between the aqueous and the chloroform phases 0.000 0.100 0.100 +0.001 0.050 0.051 in this way. Extensive tests have shown that the method -0.001 0.050 0.049 $0.001 0.050 0.051 is equally accurate a t p H values higher than 7.E-e. g., pH 0.000 0.010 0* 010 8.4 to 9.0. The latter pH may not be the upper limit of the In developing this procedure for the analysis of whole working range. The important factor in this connection is blood, numerous attempts were made under various condi- that both sample and blank must be adjusted to the same pH. tions to apply the titrimetric extraction immediately after destruction of the organic matter. A way to avoid the oxi- TABLE111. DETERMINATION OF ADDEDLEADIN BEEFBLOOD dation of the dithizone reagent by ferric iron in the presence (In these experiments the lead, as lead nitrate, was added by another chemist in amounts unknown to the analysts.) of potassium cyanide could not, however, be found. ReTOTALLEAD ADDFID L~AD course was then had to a preliminary dithizone extraction LEAD ADDED FOUND RBCOVERED ERROR Me. Mo. Me . Mg. for separating the lead, in which the partial destruction of the 100-GRAM BLOOD BAYPLEB reagent is of no importance, after which the titrimetric ex0.210 0,247 0.207 -0.003 traction can be made without interference. Table I1 indi0.200 0.241 0.201 +0.001 0.110 0.148 0.108 -0.002 cates the completeness with which lead is separated from 0.100 0.140 0.100 0.000 0.050 0.093 0.053 4-0.003 relatively large amounts of iron by using this double-ex0.050 0.086 0.046 -0.004 traction procedure. 0.011 0.051 0.011 0.000 during the preliminary testing of the titrimetric-extraction procedure when applied directly to pure solutions of lead chloride and lead nitrate.
TABLE11. DETERMINATION OF LEADIN THE PRESENCE OF 1.0 GRAM OF IRON AS FERRIC SULFATE LEADADDED TOTALLEADFOUND Me. Me. 0.100 0.152 0.100 0.154 None Blanks None
8
}
ADDEDLEAD RECOVERED ERROR Mi7. Me. 0.099 -0.001 0.101 $0.001
...
....
In these experiments the lead, in the form of nitrate, was added t o ferric sulfate, and after the addition of 2 ml. of concentrated sulfuric acid (sp. gr. 1.84) the solution was eva orated to copious fumes of sulfur trioxide. After cooling, 50 mf of water and 10 grams of citric acid were added, the latter for the purpose of preventing the preci itation of iron when the solution was subsequently made alkagne. Equally good lead recoveries were obtained in another series of experiments in which amounts of lead, as the nitrate, ranging from 0.1 to 0.5 mg., were added to samples of 0.10 gram of iron as ferric nitrate. In each instance 2 grams of citric acid were added, the alkalinity of the solution was properly adjusted, and the sample then handled by the doubleextraction procedure. This finding is at variance with the statement of Allport and Skrimshire ( I ) that nitrates interfere with the complete extraction of lead, particularly in the presence of a large proportion of iron. The results in Table I11 represent a few of the tests performed upon leaded blood specimens during the preliminary development of the method. Experience with the technic has enabled similar analyses to be made with a substantially consistent error not exceeding =tO.OOl mg. of lead. The analyses made on the 15-gram blood samples are particularly interesting in that three analysts collaborated, each working independently of the others.
DISCUSSION It is important that the digestion residue be completely dissolved before attempting initial lead separation, since otherwise lead adsorption, with resultant lead loss, is likely to occur. The sodium chloride-hydrochloric acid solution not only is an excellent solvent for lead sulfate, but has also dissolved all other residues remaining after digestion. Some of these were resistant to citric acid and/or ammonium citrate, even upon prolonged heating.
None None 0.008 0.010 0.010 None
t::::} Blanks
0.036 0.038 0.039
:::?ji} Blanks
...
....
0.007 0.009 0.010
-0.001 -0.001 0.000
...
....
60-QRAY BLOOD SAMPLES
0.115 0.077 0.045 None
0.135 0.100 0.065 0.019 Blank %GRAM
0.0040
0.004b 0.055” 0.055; 0.055 None0 Noneb Nonee 0 Analyst F. b Analyst E. 0 Analyst C.
0.024 0.021 0.076 0.073
0.019
0.116 0.081 0.046
...
+O.OOl +0.004
+O.OOl
....
BLOOD SAMAPL18
0.005 0.004 0.057 0.056 0.054
...
+O.OOl 0.000 $0.002
+O.OOl -0.001
....
Unless constant care is exercised throughout the entire procedure to avoid lead contamination, consistent accuracy cannot be obtained. A likely source of contamination is in the handling of the separatory funnels. The authors have found it distinctly advantageous to wire the stopper to the neck of the separatory funnel with a loose loop of copper wire, which permits easy removal of the stopper but does not allow it to hang in contact with the sides of the funnel. The ground-glass surface must not come in contact with the fingers or other contaminants. Whereas it is preferable not to lubricate the stopper-the water seal is entirely satisfactory-the stopcock may be coated with a thin film of Lubriseal. Once a separatory funnel has been brought into active use, it is protected from dust, fumes, etc., between analyses. Before being used again it is only necessary to wash with dilute nitric acid and then test with dithizone solution No. 2 as described under “Glassware and Reagents,” to insure the complete absence of lead contamination. In the experimental work reported above, bismuth was considered the only interfering element likely to be present. If the beef blood used in this study contained bismuth, it is apparent that it did not interfere with the satisfactory recovery of added lead. Experimentation is now under way
INDUSTRIAL AND ENGINEERING CHEMISTRY
36
t o extend the applicability of the method to biological materials containing bismuth , LITERATURE CITED (1) Allport, N. L., and Skrimshire,G. H., Analyst, 57, 440 (1932). (2) Avery, D., Hemingway, A. J., Anderson, V. G., and Reed, T. A., Proc. Australasian Inst. Mining & Met., No. 43, 173-99 (192 1). Bernhardt, H., 2. anal. Chem., 67, 97 (1925-26). Bishop, W. B. S., and Cooksey, T., Med. J . Australia, 660-2 (November 9. 19291. (5) Bohnenkamp, H., and Linneweh, W., Deut. Archh. klin. Med., 175, Heft2, 157 (1933). (6) Cooksey, T., and Walton, 5.G., Analyst, 54, 97 (1929). (7) Fairhall, L. T., J. Ind. Hyg., 4,9 (1922). (8) Fischer, H., Wiss.Ver6,ffentlich.Siemens-Konzern, 4, Heft 2, 158 (3) (4)
(1925); Z. angew. Chem., 42,1025 (1929); Mikrochemie, 8,319 (1930).
Fischer,' H., and Leopoldi, G., Wise. Ver6ffentZich. SiemensK o n z a , 12, Heft 1,44 (1933). Francis, A. G., Harvey, C. O., and Buchan, J. L., Analyst, 54, 725 (1929).
Goode, E. A., and Summers, W. H., SOC.Chem. Ind. Victoria, Proc., 32, 686 (1932).
Vol. 7, No. I
(12) Hevesy, G. V., and Hobbie, R., 2. and. Chem., 88, I (1932). (13) Iv~SOW, V. N., Chm.-Ztg., 38,450 (1914). (14) Jones, B., Analyst, 55, 318 (1930). (15) Ibid., 58, 11 (1933). (16) Kehoe, R. A., et al., J . A m . Med. Assoc.. 87. 2081 (1926): 92. 1418 (1929). (17) Lucas, R., and Grassner, F., Mikrochemie, Emich Festschrift, 197 (1930). (18) Newman, R. K., Med. J. Australia, 781-5 (February 8, 1930). (19) Ross, J. R., and Lucas, C. C., Can. Med. Assoc. J.,29, 649 (1933). (20) Schiitz, F., and Bernhardt, H., 2. Hyg. Injektionskrank., 104, 441 (1925). /91\ Seelkopf, K., and Taeger, H., Z. ges. exp. Med., 91,539 (1933). Seiser, A., Necke, A., and Muller, H., 2.angew. Chem., 42, 96 (1929). (23) Tannahill, R. W., Med. J . Australia, 1929, I, 195-208; 216-7 (February 16,1929). (24) Topelmann, H., J.prakt. Chem., 121, 289 (1929). (25) Wichmann, H. J., et al., J . Assoc. OficiaZ Agr. Chem., 17, 108 (1934).
.
I
&$
RECEIVED November 17, 1934. This work was supported by The Eliaabeth Storck Kraemer Memorial Fund created by Pierre S. and Lammot du Pont. Presented before the Division of Biological Chemistry at the 88th Meeting of the American Chemical Society, Cleveland, Ohio, September 10 to 14, 1934.
Selenite-Phosphate Method for Determining Zirconium in Ores STEPHEN G. SIMPSON WITH WALTERC. SCHUMB, Massachusetts Institute of Technology, Cambridge, Mass.
T
HE selenitemethod has been shown to be capable of giving accurate results and to be applicable to the determination of zirconium in ores (3) and in alloys (1). It is somewhat longer than the phosphate method, but the freshly precipitated zirconium selenite is soluble in hydrochloric acid and errors of co-precipitation can be readily eliminated by a second precipitation before ignition to the oxide. A combination of the two methods would seem to have certain advantages over either method alone: over the phosphate method, in that two independent precipitations of the zirconium can be made easily without resort to intermediate fusion, and the effect of co-precipitation can thus be made negligible; over the plain selenite method, in a shortening in the time of analysis without appreciable sacrifice of accuracy. Such a combination method has been found applicable to the determination of zirconium in steels (2). When applied to ores, it would be particularly advantageous where thorium is present. Thorium, when present alone, is unprecipitated by either phosphate or selenite under proper acid concentrations, but it is very badly co-precipitated by either method when present with zirconium. Previous removal of thorium as oxalate in the selenite method was found to require several extra steps to bring the solution to a state suitable for the precipitation of zirconium selenite, but these would not be necessary if thorium were removed following a selenite precipitation and prior to a phosphate precipitation, for the sulfuric acid used to destroy the excess oxalate serves as the proper medium for the precipitation of zirconium phosphate. Decompose the ore and reci itate the zirconium once as in the plain selenite method f f thorium is present, dissolve the precipitate in a mixture of 40 cc. of 10 per cent oxalic acid solution and 12 cc. of 6 N hydrochloric acid. Filter off the thorium oxalate and destroy the excess oxalate by evaporation with 50 cc. of 18 N sulfuric acid, as in the selenite method. If thorium is absent, dissolve the zirconium selenite recipitate in 60 cc. of 18 N sulfuric acid. In either case dilute t i e sulfuric acid solution to 200 cc. and filter off any precipitated selenium. If a small amount of red selenium runs through the paper it
8).
may be neglected. Heat the solution to 50' C., and add 20 cc. of 3 per cent hydrogen peroxide and 50 cc. of a 20 per cent
solution of diammonium phosphate, precipitating zirconium phosphate. Allow to stand 2 hours, filter, wash thoroughly with a 5 per cent solution of ammonium nitrate, and ignite slowly. Gradually raise the temperature to the full heat of the Tirrill burner and weigh as ZrPzOr. The reproducibility of the method is illustrated by the analysis of zirconium concentrates which gave the following values for the percentage of ZrOz present: 50.88,51.10,50.87, and 50.50; average, 50.84. When applied to samples of ores, the method was found to be rapid and accurate. Results obtained on samples made by mixing known amounts of zirconium dioxide with varying amounts of feldspar, apatite, thoria, etc., are shown in Table I. TABLEI. ANALYSISO F ARTIFICIAL ZIRCONIUM ORE8 SELENITE-PHOSPHATE METHOD ZrOz Feldspar
%Ye
Ti02 NHiVOa CeOn Sample ZrPeO7 found Zr0z calcd.
ZrOt resent ZrOe round
Gram 0.1103 0.30 0.10
..... ... .... ....
0.5106 0.2355 0.1093
%
21.60 21.42
Uram 0.1185 0.25 0.10 0.050
.... .... .... 0.5208
0,2551 0.1184
%
22.76 22.75
Gram 0.1007 0.20 0.050 0.050 0.050
.... ....
0.4520 0.2160 0.1003 % 22.25 22.19
Gram 0.1221 0.20 0.050
....
0.050 0.050
....
0.4720 0.2640 0.1226
%
25.89 25.99
Gram 0.1225 0.15 0.050 0.050
0.050
0.050 0.050 0.5230 0.2656 0.1233 % 23.42 23.58
BY THB Qram
0.102s 0.15 0.050 0.050 0.050 0.050 0.050 0.5010 0.2224 0.1033
%
20.61 20.62
LITERATURE CITED (1) Simpson, 5. G., and Schumb, W. C., IND.ENQ.CHBM.,Anal. Ed., 5, 40 (1933). (2) Ibid., 5, 211 (1933). (3) Simpson, S. G., and Schumb, W. C., (1931).
RECBIVEDJuly 24, 1934. Inorganic Chemistry.
J. Am. Chem. SOC.,53, 921
Publication No. 46, Researah Laboratory of
