had been rinsed with an aqueous solution of heparin. The blood samples were extracted and analyzed by the chemical reaction Procedure I with the results presented in Table V. Blood levels of the four tolylsulfonylurea analogs 11, 111, IV, and V (see Table I) were determined in rats following single oral doses of 100 mg. per kg. of each compound. Each compound was administered in the form of a solution of dilute sodium bicarbonate by stomach tube to a group of 8 rats. The rats of each of the 4 groups were sacrificed by decapitation a t 1, 2, 4, and 8 hours. The bloods, collected in heparinized tubes, were analyzed in duplicate by extraction and Procedure I. The found blood lei-els for each compound are plotted semilogarithmically against time in Figure 1, A-D.
ACKNOWLEDGMENT
The author is indebted to Bernard Koechlin and Arthur Stempel for their helpful counsel and critical review during the course of this work and the preparation of the manuscript, and to George Tryon for his competent technical assistance. The sulfonylurea compounds were prepared and made available t o us by *\rthur Stempel of the Department of Chemical Research, Hoffmann-La Roche, Inc. LITERATURE CITED
(1) Aeschlimann, J. A,, Stempel, A,,
U. S. Patent 2,928,871 (March 15,
1960). (2) Bladh, E., Korden, A., Acta Pharmacol. Toricol. 14, 188 (1958).
(3) Carmichael, R. H., Clin. C'hem. 5, 597 (1959). (4) . , Chulskv. T., J. Lab. Clin. M e d . 53, 490 f 19581', (5) Forist, 'A. A,, Miller, Jr., W. L.,
Krake, J., Struck, W. A., PTOC.SOC. Exptl. Biol. Med. 96, 180 (1957). ( 6 ) €hack, E., Hagedorn, A., Ruschig, H., Korger, G., U. S. Patent 2,964,560 (December 13.1960). ( 7 j Marshall, F: J., Sigal, h4. V., J . Org. Chem. 23, 927 (1958). (8) McDonald, J. J., Sawinski, V. J., Teras Rept. Biol. Med. 16,479 (1958). (9) Ruschig, H., Aumuller, W., Korger, G., Wagner, H., Schola, J. Bander, .4., U. S. Patent 2,968,158 (January 17, 1961'1. (10) Spingler, H., Klin. Wochschr. 35, 533 (1957). (11) Spingler, H., Kaiser, F., ArmeimittelForsch. 6, 760 (1956). (12) Toolan, T. J., Wagner, R. I,., Jr., Ann. N . Y . Acad. Sci. 7, 449 (1959). RECEIVEDfor review July 23, 1962. Accepted November 9,1962.
Application of Ion Exchange to Analysis of Phosphate Rocks H. N. S. SCHAFER Division o f Coal Research, Commonwealth Scienfific and lndusfrial Research Organization, Chatswood, New South Wales, Ausfralia
b A simple procedure i s described in which the finely ground rock sample is readily dissociated by shaking in water with a cation exchange resin; phosphorus and fluorine are quantitatively brought into solution. After filtration, the phosphorus and fluorine contents of the filtrate can be determined directly using simple spectrophotometric procedures phosphorus via the yellow molybdovanadophosphate complex and fluorine via the blue complex formed between fluoride ions and the cerium(ll1) chelate of alizarin complexone. Calcium may be eluted from the resin with hydrochloric acid and determined free from phosphate interference b y (ethylenedinitrilo) tetraacetic acid titration.
-
T
phosphorus and fluorine contents of phosphate rocks are usually determined on separate samples (6). The present paper reports the use of a cation exchange resin to bring phosphorus and fluorine into solution simultaneously and quantitatively under conditions that greatly facilitate determination of these elements. Cation exchange resins have been used successfully t o dissociate ionic solids of lorn solubility. The carbonates, sulfates, and phosphates of the alkaline earth metals have been dissociated, in order t o bring the anions or HE
indirectly the cations into solution (1, 8, 7 , 9-18). It was considered that such an approach might be applicable t o phosphate rocks. Further, Scheffer (IC), during investigations of phosphorus uptake by plants, demonstrated that phosphorus, as phosphate, was transferred t o the anion exchange resin when a number of phosphate rocks were shaken with a mixture of cation and anion exchange resins in water; but he failed to explore the analytical possibilities of this approach. DEVELOPMENT OF METHOD
Seven phosphate rocks from various locations were examined, as well as National Bureau of Standards phosphate rock (Tennessee Brown) 56b. The phosphorus and fluorine contents of these seven samples as determined by normal decomposition procedures are given in Table I, and for the Bureau of Standards sample in Table 11. The cation exchange resin used mas Zeo Karb 225, hydrogen form (Permutit, London). This is a sulfonated crosslinked polystyrene in bead form, having a total exchange capacity of 5 meq. per gram. To establish the optimum conditions for decomposing a phosphate rock with this resin, weighed portions (0.05 gram) of each sample and 5 to 10 grams of the resin were placed with 35 ml. of distilled water in a plastic bottle, which was shaken for various times up
to 24 hours a t room temperature, and at an initial or maintained temperature of about 80" C. (limit set by pressure buildup in the bottle). The resin was then separated from the solution by filtration through a plastic filter into a plastic beaker. The filtrate was neutralized and analyzed for phosphorus and fluorine, using the procedures described below. The efficiency of each exchange procedure was gaged by comparing the phosphorus contents of the filtrates with the value obtained for each sample via acid digestion (0.05gram sample, 10 ml. of concentrated HC1, and 4 ml. of 707, perchloric acid) using the same spectrophotometric finish; in addition, the fluorine contents of the filtrates were compared with the values obtained for each sample by a normal distillation procedure (6). For the NBS phosphate rock, comparison was made with the recommended values. The samples examined fell into t n o groups: For all but two samples (3 and 4, Table I) virtually all the phosphorus and fluorine were present in solution after only 2 hours' shaking with the exchange resin when the initial water temperature was 80" C. With samples 3 and 4, decomposition was complete after shaking continuously for 16 hours with the temperature maintained a t 80" C. The behavior of each group is typified by the effect of conditions on phosphorus and fluorine VOL. 35, NO. 1, JANUARY 1963
53
Table I.
Sample
pzo5, %
Ion exchange
Acid, decompositiona
no.
decomposition
1
37.60\ 37.66J 37'63
37.54
2
i::;:38.64 )
38 76 38:90) 34.55' 34.58) 33 11 32:89) 20.88'1 20.863 15 95 15:96) 35.87 35.91)
34.84 34.87) 34'86 32.96' 33.10) 33'03 20.54 20.63) 20'58 15.56 15.52) 15'54 35.80 35.76) 35'78
3 4 5 6 i
Analysis of Phosphate Rocks
F, %
Ion exchange
decomposition
!:E)
Distillation procedure
70Fe203+ A1,O3
% Fez03
Calcd. yo A1203
3.07
3.15
0.65
0.28
0.37
2.65
0.51
0.22
0.29
1.46
20.75
6.03
14.72
I .01
23.50
7.06
16.44
20.87
2.58'1 2.593 2'59 1.28' 1.311 1'30 0.93! 0.891 O"' 2.05'1 2.141 2'10
2.19
27.40
21.50
5.90
15'96
I . 68,
1.57
35.00
30.39
4.61
3.6i
3.95
2.73
1.22
38'83 34.56 33.00
1 67
35'89
0.05-gram sample decomposed with hydrochloric acid-perchloric acid, filtered, and made to 200 ml. Phosa Acid decomposition. phorus determined by spectrophotometric method of Gee and Deitz (6).
Table II.
Analysis of NBS Phosphate Rock 56b
NBS
Constituent
Ion exchange method, yo
value,
P205
31 57 6 1 [ 3 1 59
31.55
3 3 3 3 98 1/ 3 39
3 4
44 09 43 98 1 4 4 04
44 06
F
CaO
5%
recovery noted in Table I11 for samples 1 and 3. [In the recommended procedure overnight shaking (16 hours) has been specified, since it was convenient in the particular conditions of the present investigation. However, 2 t o 4 hours' shaking should be adequate for phosphate rocks not containing aluminum phosphate. I n the presence of the latter, where it is necessary t o main-
Table 111.
tain a temperature of SO" C., complete decomposition should be possible with less than 16 hours' shaking.] The filtrates obtained following the cation exchange decomposition of samples 3 and 4,under conditions in which recovery of phosphorus and fluorine was incomplete, were milk-white in appearance and gave a white precipitate on centrifuging. Spectrochemical analysis showed that these residues consisted principally of aluminum and phosphorus, which suggested that the presence of aluminum phosphate was responsible for the difficulties experienced with the samples. The high aluminum contents of samples 3 and 4 (see Table I) are consistent with this assumption. The data for sample 3 in Table I11 show that fluorine was more readily recoverable than phosphorus, a result which is consistent with the former's
Ion Exchange Decomposition of Phosphate Rocks under Various Conditions
Sample
Treatment"
NO. 1 (37.44% P i 0 5 by
A
acid decomposition)
B
Shaking time, hr. 16 24 1 2 4
No. 3 (34.56% P?Osby acid decomposition)
A
8 16 24
P206,%
F, %
37.60 37.66 37.40 37.70 37.64 37.64 22.75 25.59
2.91 2.96 2.98 3.07 3.06 3.00 1.31
1.21
C 16 34.84 1.28 A. 0.05-gram sample, 7 gram resin, 35 ml. cold distilled water. B. 0.05-gram sample, 7 gram resin, 35 ml. hot (80' C.) distilled water. C. 0.05-gram sample, 7 gram resin, 35 ml. hot distilled water, and temperature maintained at 80' C. throughout shaking period.
being associated with the phosphorus of calcium phosphate. A slight opalescence was observed in the filtrates from all samples, even when recovery of phosphorus and fluorine was complete. The opalescence could be eliminated by centrifuging if desired, but its presence did not appear t o affect the subsequent analytical determinations. EXPERIMENTAL
Apparatus. A Unicam S P 600 spectrophotometer (Unicam Instruments, Ltd., Cambridge, England) was used for all absorbance measurements. Reagents. Ion exchange resin Zeo Karb 225 hydrogen form was used. .ilternatively, resins such as Amberlite IR-120 (Rohm and Haas Co., Philadelphia, Pa.) or Dowex 50-XS (Dow Chemical Co., Midland, Mich.) may be used. PHOSPHORUS. Solution 1, 8% w./v. ammonium molybdate tetrahydrate in distilled water. Solution 2, 0.4% vv./v. amnionium 6112 metavanadate in aDuroximatelv .& perchloric acid. Prepare both solutions as described' bv Gee and Deitz (6). Mix eclual vGlumes of solutions 1 and 2 prior to. use, by pouring solution 1 into solution 2; stir t o dissolve any precipitate' formed. Phosohorus standard. Drv Dotassium dihydrogen phosphate at 105' C. Weigh 0.4388 gram, dissolve in water, and dilute t o 1 liter. This solution contains 0.1 mg. of phosphorus per ml. FLUORINE.Alizarin complexone, 0.0005f71 (alizarin complexone, 1,2dihydroxyanthraquinon - 3 - ylmethylamine-N,N-diacetic acid, Hopkin and Williams, Ltd., Essex, England), cerous nitrate 0.0005M, sodium acetate-acetic . acid buffer, pH 4.6,is prepared as described by Johnson and Leonard ( 8 ) . Fluoride standard. Stock solution. Dissolve 0.221 gram of sodium fluoride 1
54
a
ANALYTICAL CHEMISTRY
in distilled water, dilute to 1 liter. Working standard. Dissolve 0.2194 gram of dry potassium dihydrogen phosphate in distilled water, add 100 ml. of stock fluoride standard, and dilute to 1 liter. This solution contains 10 pg. of F per ml. and 50 pg. of P per ml. RECOMMENDED PROCEDURE
Tlie procedure finally adopted for the decomposition and analysis of phosphate rocks was as follows: Decomposition of Sample.
Trans-
f r r 0.05 gram of finely ground phos-
phate rock previously dried for 1 hour a t 10.5" to 110' C. to a 100-ml. plastic bottle, together with 5 t o 10 grams of Zeo Karb 225 hydrogen form resin (0.2 to 0.4 mm.) and 35 ml. of hot (80" C.) distilled water. Seal the bottle with a tightly fitting plastic insert and then with the screw cap. Shake overnight on a mechanical shaker. Separate the resin from the solution by filtration through a Whatman No. 3 paper on a plastic Buchnertype filter similar to that recently described by Brown, Durie, and Schafer ( 4 ) . Collect the filtrate in a plastic bcaker. Itrash the resin thoroughly with about 100 ml. of distilled water, collecting the washing with the filtrate. Yeutralize the filtrate with O.1N sodium hydroxide, using phenolphthalein as indicator. Filter through a Whatman No. 42 paper into a 200-ml. volumetric flask and make to volume. Retain the resin for regeneration and for cation analysis if required, If the filtrate obtained using the above conditions is clouded or the presence of aluminum is suspected, keep the temperature of the suspension of sample and resin a t about 80" C'. throughout the period of shaking. This can be achieved by sheathing the flask in an aluminum sheet and winding around this an insulated heating cord-an Electrothermal Thermocord, for example. The plastic bottle must have a cap which seals tightly and shaking must be maintained to prevent, localized overheating, which might cause the plastic bottle t o soften and burst. Tlie use of plastic ware is recommended for all operations up to the neutralization step, to ensure that the hvdrogen fluoride released as the phosphate decomposition proceeds is not lost by attack on glassivare Phosphorus Determination. Phosphorus is determined using the differential spectrophotometric procedure of Gee and Deitz ( 5 ) . When it is applied to the filtrate from the ion evchange procedure, high results can br obtained if silicon is present in the solution. owing to the hydrofluoric acid formed rcacting with silica to give fluosilicate. The remedy is to evaporate the aliquot to dryness, treat the residue with hydrochloric acid, and remove silica by filtration. Pipet 20 to 40 ml. of sample solution containing approximately 0.6 to 0.8 mg. of phosphorus into a 100-ml.
beaker, add 2 ml. of concentrated hydrochloric acid, and evaporate just to dryness. Cool, add 0.5 ml. of hydrochloric acid and 10 nil. of distilled water, and boil for 15 minutes. (This procedure is necessary to reconvert any pyrophosphate, formed on evaporating to dryness, to orthophosphate.) Filter the solution (Whatman KO. 41 paper) and wash well with hot distilled water, collecting filtrate and washings in a 50-ml. volumetric flask. Cool, add 4 ml. of mixed reagent, and dilute t o volume. Complete the determination of phosphorus by using the differential spectrophotometric procedure of Gee and Deitz ( 5 ) . Fluorine Determination. Determine fluorine in the filtrates obtained after the ion exchange procedure, using Johnson and Leonard's (8) modification of the method developed by Belcher, Leonard, and West ( 2 ) , which utilizes the color developed by fluoride with the complex formed by alizarin complexone and cerous nitrate. The method is readily applicable to the filtrates, since no cations are present other than sodium and since phosphate, unless present in excessive amounts, does not interfere. However, as a precaution, add phosphate to the fluoride standard at a level approximating that obtained for the phosphate rocks. Transfer a 3- to 5-ml. aliquot of the filtrate from the ion exchange procedure t o a 100-ml volumetric flask and dilute t o 50 ml.; add in turn 10 ml. of alizarin complexone, 3 ml. of buffer solution, and 10 ml. of cerous nitrate, swirling the flask after each addition. Make up to volume and mix well. Allow samples to stand 1 hour. Read the absorbance in 2-em. cells a t 610 mp against a reagent blank. At the same time, prepare standards containing 10, 20, and 30 pg. of fluoride, and carry out the above procedure. Plot the absorbance a t 610 mp lis. fluoride content and read off the fluoride content of the samples. Calcium Determination. Transfer the resin from the ion exchange decomposition of the rock to a suitable ion exchange column. Elute with 100 ml. of 3Ar hydrochloric acid. Evaporate the eluate to dryness, cool, dissolve residue in 4 nil. of concentrated hydrochloric acid and 20 ml. of water, and make to 100 ml. in a volumetric flask. Titrate a suitable aliquot (25 to 30 ml.) with 0.01Jf EDT-4, using Calcein as indicator.
via acid extraction. The slightly higher values obtained using the latter procedure for samples 5 and 6 may probably be attributable to the high iron contents of these samples. Iron, which would be present in the solutions from the aciddigestion procedure, interferes with the photometric method used (6) for phosphorus, giving high results. The very satisfactory agreement obtained between the present (ion exchange) result and the recommended phosphorus content for the NBS phosphate rock provides a good indication of precision attainable with the ion exchange procedure. With the precautions outlined, no difficulty is experienced due to the presence of aluminum phosphate. The fluorine contents determined via ion exchange compare favorably with those obtained in another laboratory by the distillation procedure. The agreement with the recommended value for the fluorine content of the NBS phosphate rock provides further confirmation of the reliability of the ion exchange procedure. Although no detailed investigation was made of the use of the ion exchange procedure for the determination of calcium, the result for the NBS phosphate rock (Table 11) shows that the method is satisfactory for this determination. It should be equally applicable to the determination of other cations as phosphate or carbonatesaluminum and iron, for example. The ion exchange procedure possesses several advantages: The exchange can be completed overnight without attention; several samples can be processed simultaneously; phosphorus and fluorine can be determined without interference from cations, and calcium without interference from phosphate. The method was originally developed in an attempt to determine phosphorus and fluorine directly in bituminous coals, and proved successful in a number of cases. The results of this latter application will be reported elsewhere. Thp method should be applicable to the decomposition of basic slag, phosphate fertilizers, tooth, and bone, for determining phosphorus and, when applicable, fluorine.
RESULTS AND DISCUSSION
ACKNOWLEDGMENT
The phosphorus and fluorine contents obtained for the seven phosphate rock samples when analyzed by the above method are compared in Table I with the results obtained using the alternative methods indicated. The phosphorus, fluorine, and calcium contents obtained by the present method for XBS phosphate rock 56b are compared with the recommended values in Table 11. The phosphorus values obtained via ion exchange show good reproducibility and agree well with the values obtained
The author expresses his appreciation to K. Norrish, C.S.I.R.O. Division of Soils, Adelaide, South A4ustralia, for supplying the phosphate rock samples; to D. Bowdich, Australian Mineral Development Laboratories, Adelaide, South Australia, for making available some of the analytical data used for comparison (fluorine contents by distillation and titration with thorium nitrate, and ferric oxide plus aluminum oxide contents); to M. C. Clark, for spectrochemical analyses; and R. A. VOL. 35, NO. 1, JANUARY 1963
55
Durie and D. J, Swaine, for helpful discussions. LITERATURE CITED
(1) Aleskovskii, V. B., Kalinina, T. I.,
Trudy Leningrad Tekhnol. Inst. im. Lensoveta No. 35, 178 (1956). (2) Belcher, R., Leonard, M. A., West, T.S., J. Chem. SOC.1959, 3577. (3) Brochmann-Hanssen, E., J . Am. Pharm. Assoc. 43, 307 (1954). (4) Brown, H. R., Durie, R. A., Schafer,
H. N. S., Fuel (London)38, 295 (1959). (5) Gee, A., Deita, V. R., ANAL. CHEM. 25, 1320 (1953). (6) Hillebrand, W. F., Lundell, G. E. F., Bright. H. A,. Hoffman, J. I., ‘LAmlied Inoyganic Analysis,” 2nd ed., Wiley, New York, 1953. (7) Honda, M., Yoshino, Y., Wabiko, T., J . Chem. SOC.Japan, Pure Chem. Sect.
(10) Osborn, G. H., Analyst 78, 220 (1953). (11) PiBce, R., Rev. Math-. Constr. Trav. Pub. No. 524, 107 (1959). (12) Samuelson, O., Svensk Kern. Tidskr. . 53, 60 (1941): ‘ (13) Zbid., 57, 158 (1945). (14) Scheffer, F., Kloke, A., Wittkopf,
G., Z. Pjlanzenernahr. Diing. Bodenk. 79, 232 (1957). 73, 348 (1952). (8) Johnson, C. A., Leonard, ?* A.,I. Analyst 86, 101 (1961). (9) Koblyanskir, A. G., J . Gen. Chem. RECEIVEDfor review July 23, 1962. Accepted October 18, 1962. USSR 24, 17 (1954).
Determination of Refractory Metals in Ferrous Alloys and High-Alloy Steel by the Borax Disk X-Ray Spectrochemical Method C. L. LUKE Bell Telephone Laborafories, Inc., Murray
b X-ray spectrochemical methods have been developed for the determination of Mol W, Nb, and Ta in heat-resisting and corrosion-resisting alloys and of Mo and W in high-alloy steel. The refractory metals are separated from the bulk of the alloy matrix by conventional chemical separations, converted to oxides, fused in borax, and then determined by x-ray spectrochemical analysis. The methods are convenient, rapid, and yield excellent results.
T
of Mo, W,Nb, and T a in ferrous alloys and steel is a difficult and time-consuming analysis because of the similarity in the chemical behavior of these refractory metals. In recent years, matters have been greatly improved by the use of anion exchange techniques to effect the necessary separations. In the analysis of heat-resisting and corrosion-resisting alloys, Bandi et al. isolate the refractory metals from the bulk of the sample by conventional gravimetric separations, combine the precipitates, and convert the metals t,o oxides before proceeding to the anion exchange separations (4). Since the latter separations are rather time consuming, a more rapid method for the final determinations would be useful. It seemed probable that considerable time could be saved by fusing the isolated mixed oxides in borax and then determining the four metals in the cooled melt by the x-ray spectrochemical method (6, 6). This has proved to be true and, as a result, a new method is proposed which is rapid, convenient, and capable of yielding results which are comparable in accuracy to those obtained by other methods. The method has also been adapted to the analysis of
Hill, N . J . refractory metals in several other metals and alloys. The usefulness of the chemical separation x-ray analysis method for extending the sensitivity of x-ray methods in general or for facilitating the analysis of samples which are difficult to analyze by chemical or x-ray methods alone has been demonstrated previously (7, 8). In view of this, the present report will include, for the most part, only that material which has not appeared elsewhere. EXPERIMENTAL
HE DETERMINATION
56
ANALYTICAL CHEMISTRY
Apparatus. A General Electric x-ray spectrometer with a Pt target, a LiF crystal, a 10-mil Soller slit, a x 3/4-in~hA1 mask, and a scintillation counter was used. The gas-oxygen burner was supplied by Bethlehem Apparatus Co. of Hellertown, Pa. (Burner No. PMZC-L). Procedure. PREPARATION OF BORAXDISK STANDARDS.Transfer the following weighed portions of the dry, powdered, reagent grade oxides of the refractory metals from black glazed paper to 30-ml. Pt crucibles. KO,
Crucible Moo3 WOs SbzOs
Ta206
so. lJ 2, mg. mg.
No.
KO.
3,
4, mg. 10.0 20.0 40.0 30.0
mg. 30.0 20.0 40.0 40.0 10.0 30.0 20.0 30.0 10.0 10.0 40.0 20.0
To each crucible add 2.0 grams of dry, powdered, reagent grade BaO followed by 10.0 grams of pure, dry, powdered borax (Na2B407). Heat on a gas-oxygen flame to fuse the mixture and then swirl vigorously for about 30 seconds or until the oxides have dissolved completely. Pour the melt onto a smooth, bare, ‘/*-inch A1 plate which
is maintained a t a temperature of about 180’ C. Remove the A1 plate from the hot plate and allow t o cool. Keep the disks in a desiccator when not in use. DISSOLUTION OF S A m L E . To analyze heat-resisting alloys such as KBS 167 and 168, transfer 0.50 gram of the subdivided sample to a 100-ml. Pt dish. Add 10 ml. of HF-HN03 solution I) and cover with a flat, round (2 polyethylene bottle rest. Heat gently until dissolution of the sample is complete. Wash and remove the cover and evaporate the solution just to moist dryness. Add 5 ml. of water, heat, and swirl to dissolve soluble salts. K i t h the aid of a steel reinforced polyethylene stirring rod, wash the solution and precipitate into a 400-ml. beaker containing 10 ml. of HClO,. Evaporate rapidly to expel volatile acids. R hen fumes of KC104 begin to be evolved, flame the sides of the beaker t o expel all traces of HF and then take to copious fumes t o destroy carbides and to oxidize Cr and V. When the HClO4 condenses about two thirds of the way up the mall of the beaker, cool, add 10 ml. of HC1, cover, and heat to boiling to dissolve soluble salts and to reduce Cr and V. Avoid excessive loss of HCl. When most of the oxidizing fumes have been expelled, add 180 ml. of water. To analyze corrosion-resisting alloys such as NBS 123a and 123b, dissolve 4.00 grams as completely as possible in a covered 400-ml. beaker in 50 ml. of HCl by heating gently. Carefully add 5 ml. of HN03 in small portions to oxidize the Fe. Then add 1 ml. of H F and 25 ml. of HClO4. Evaporate rapidly to copious fumes. Cool, add 20 ml. of HC1, cover, heat t o boiling, and add 250 ml. of water. T o analyze high-alloy steel, dissolve 0.15 to 0.30 gram of the sample in 5 ml. of HN03 plus 5.0 ml. of niobium solution (dissolve 1.00 gram of hTbz06 in 25 ml. of HF and dilute to 100 ml.) in a 400-ml. beaker. Add 10 ml. of HC104,
+
