4th Annual Summer Symposium-Standards
Emission Spectrographic Standards BOURDON F. SCRIBNER AND CHARLES H. CORLISS National Bureau of Standards, Washington, D . C .
Spectrographic analysis, basically a comparative method, requires standard samples matching test samples closely in composition, form, and physical condition. Certain nonmetallic standards, such as ores, glass, and minerals, prepared for use in chemical analyses often serve equally satisfactorily for spectrographic analysis. For high speed and high accuracy in the analysis of metals and alloys, standards are required in forms suitable for direct use as electrodes-i.e., rods or plates. Careful attention is given to the preparation and testing of these standards to ensure chemical and physical uniformity. Studies are made of longitudinal and radial homogeneity and, if satisfactory, the standard is sub-
a
S
PECTROGRAPHIC analysis, in common with other instrumental methods, is basically a comparative method and standard samples are required which match the test sample closely in composition, form, and physical condition. Certain nonmetallic standards such as ores, glass, and minerals prepared for use in chemical analysis often serve equally satisfactorily for spectrographic analysis. Furthermore, with the application of techniques in which samples are taken into solution, standards may be synthesized from metals and salts of high purity. However, for high speed and high accuracy in the analysis of metals and alloys, standards are required in forme suitable for direct use as electrodes-that is, rods or plates. The great bulk of spectrographic analyses now performed are in control of metal production using solid metal standards. In a few instances metallic chip samples prepared by turning or milling have been employed by compressing the chips into rod form but, in general, this is a time-consuming operation and the results of the spectrographic analyses are not so accurate as those employing solid metal electrodes. Some typical electrode combinations are shown in Figure 1 in which rod combinations, A , are shown, including solid rods and small compressed pellets of chips, larger rod, B , or plates, C, which can be treated as an extended flat surface, using the piece as one electrode and a graphite rod as the other. REQUIREMENTS FOR STANDARDS
In preparing spectrographic standard samples for general use it has been considered necessary to provide a thin rod type, 7/32 inch or 0.25 inch in diameter, and a larger rod or disk type for application in the point-to-plane electrode technique. Both types of standards are available for many of the principal commercial metals and alloys as shown in Table I, which was derived from the latest survey (3) published by the American Society for Testing Materials. An interesting observation is made in this publication on the steady increase in the number of spectrographic standard samples, ranging from 210 in 1944, 435 in 1947, to 632 in 1950. However, many more standards are required to meet the demands of this rapidly expanding field of analysis. Attention needs to be given to the possibility of simplifying the demands for standards by decreasing the variety of sizes required or by modifying excitation conditions so that different alloy types can be intercompared with a relatively small number
mitted for cooperative analysis, which may include determinations by chemical as well as by spectrographic methods. After the composition has been determined, the standard is compared spectrographically with similar standards in order to observe its behavior in analytical applications. This consistency test serves as a final check on possible errors in the assigned composition, interferences in the spectrographic procedure, or effects of physical condition of the metal. The preparation, testing, and certification of typical standards of steel, aluminum, and tin are described. Possible developments in the large scale production of cast metal standards are discussed.
of btandards. The question might be raised as to how close the diameter of electrode rods need be maintained for accurate analytical work. Studies were made in this laboratory in which steel electrodes were progressively machined to smaller diameters bettveen spectral exposures. Excitation was by means of a lowinductance, low-resistance spark with peak voltage 18 kv., capacitance 0.014 microfarad, inductance 3 microhenries, residual resistance 0.2 ohm, and Lyith 120 discharges per second. The results are shown in Figure 2 in which the log intensity ratio of analytiral line pairs is plotted against rod diameter. The curves for thc various elements are displaced vertically to separate them clearly. For line pairs in which the excitation energy for the element and internal standard lines are closely matched, as for chromium and for manganese, the change in diameter produces no significant effect down to a diameter of 6/32 inch. Honever, an appreciable effect on the spectrum is observed when lines of different excitation energies are involved, as for Fepl'/Fe1131~6,C U I ~ ~ ~ / F ~ Iand I~Z even ~ ' Jfor , lines of the two elements originating each in the neutral atom as for C U P ~ / F ~ I ~ Z ~ ~ and S ~ I Z S ~ / F ~ I In ~ ~certain ". cases, particularly for copper and silicon, it may not be possible t o match excitation energies closely with internal standard lines or, because of the need to minimize , photometric errors, unmatched lines lying close together must be
Table I.
Standard Samples in Electrode Forms (1950)
Steel
Kational Bureau of Standards Adam Hilger Co. Battelle Memorial Institute Bureau of Analyzed Samples (England) Aluminum Co. of America i f e x Smelting Co. uminium Co. of Canada Kational Bureau of Standards Dow Chemical Co. Apex Smelting Co. Aluminum Co. of America Morris P. Kirk and Son, Inc. Apex Smelting Co. Morris P. Kirk and Son, Inc. National Bureau of Standards
234 Disks 2 5 90 D i s k s 2 . 5 33 Rods 0 . 2 5 4 Disks 2 . 5 24 Rods 0 . 5 square 9 Disks 2 . 5 10 Disks 2 . 5 26 Disks 2 . 5 15 D i s k s 2 . 5 27 Disks 2 . 5 5 Rods 0 . 2 5 a n d 0 . 5
Applied Research Laboratories Douglas Aircraft Co.
10 -
Inches
Aluminum
Magnesium Zinc Lead Tin Copper
1548
31 R o d s ' / a n m d 0 . 5 19 Rods 3/11 or o/aa 15 Rods 0 . 2 6 , disks 1 8 Rods 0 . 5
560
Disks 2 . 5
V O L U M E 23, NO. 11, N O V E M B E R 1 9 5 1
1549
Table 11. Results on Tests for Manganese in NBS Spectrographic Steel Standards
Rod
Chi11
KO
No.
12D 14C 20D 65B 100 30C 30D 32B 83A
401 402 403 404 405 406 407 408 409 .'36 410 72 411 72A 412 20C 413 414
ioc
415
106 416 20R 417 72B 418
Certified Chemical Value
% 0.344 0.462 0.916 0.725 1.38 0.707 0.786 0,624 0.456 0.390 0.651 0.599 0.673 i:i3 0.484 0.637 0.520
AV.
Redetermined Chemical Value
Spectrographic Deterrnination
Deviation of Homogeneity Tests
7c
70
70
0.34 0.46 0.89
0.34 0.45 0.88 0.75 1.38 0.725 0.79 0.63 0.48 0.42 0.65 0.61 0.66 0.66 1.13 0.50 0.63 0.53
1.2 1.2 1.3 2.6 1.4 1.2 1.3 1.3 1.2 1.2 1.2 0.95 1.3 0.58 1.4 0.97 0.92 1.4
1:38
*.
0:45 0.38
.. ..
0:67 1.12
.. .. I
.
of slightly increased precision and sensitivity in some cases and the disk electrode offering increased speed and convenience in other cases.
Spectro&:$Ed Value
% 0.31 0.46 0.89 1138
0.71 0.79 0.62 0.45 0.38 0.65 0.60 0.67 0.67 1.12
0.48 0.64 0.52
used. The differences in volatility of elements also may rcquirc close control of electrode diameter or even electrode length when these factors change the rate of cooling of the electrode tip as i n thc determination of boron in steel rods by the alternating current arc ( 4 ) . Effects of volatility of elements and of variat'ions in matrix composition are minimized tvith the more sparklike discharges and itre least with lovi-induct,ance, lowresistance spark circuits. \Vhcre rod electrodes are employed it is always safer to maintain diameters t o a tolerance of within 1/32 inch. With the disk-type electrode the general dimensions have negligible effect, provided that the flat area to be sparked is sufficiently large (0.5 inch or more in diameter) and the piece is sufficiently mns.-ive to avoid overheat,ing by the electrical discharge. Here again the effects of variat,ion in matris composition may introduce error unless st~nntialdsand sample are matched closely in composition or a correction is made for the difference in behavior (e). The possi\iility of overcoming effects of differences in matrix composition by careful selection of excitat,ion conditions-for example, as demonstrat,ed for copper alloys (5)-offers promise in reducing the number of alloy standards required. The use of both rod and disk clcctrodes will probably cont'inue, the rod having advantages
PREPARATION OF S T A N D A R D S
The preparation of solid metal standards requires three steps: preparing the metal in a suitable shape with provisions for obtaining high homogeneity; testing the metal for homogeneity; and analyzing the standard by chemical or spectrographic methods to establish its composition. The preparation of some standards such as lom~-alloysteels is relatively simple in that sections of large ingots may be rolled or drawn to size. On the other hand common cast iron cannot be fabricated in this manner and offers a greater problem in obtaining satisfactory standards in sufficient quantity. As an example of the preparation of steel etandards, the first set of standards prepared by the National I3ureau of Standards was obtained from the cores remaining after chemical chip standards were machined from &inch rounds. The cores were hot rolled to diamrters 9/32 and 9/16 inch, respectively, and centerless-ground to 7/32 and 1/2 inch by the Bethlehem Steel Co. In the authorb lahoratory the homogeneity of the rods along their length was studied by spark excitation, and only those lots showing high homogeneity were analyzed and issued as standards The results of tests on the final standards are shown in Table 11.
1
.--.--
C.2818 Fc 2811
u n
Fe3417 F e 3 1 16
I E
Cu3274 Fe 3280
n
Cu3274
I
FC
I
3266 I
~~
2
4
Figure 2.
c/
A
C
Figure 1. Electrode Assemblies Employed in Spectrochemical Analysis A. E.
c.
R o d , '/d- or '/a-inch diameter, to 6 inches long Rod, '/a-inch diameter I/( to 6 inches long Irregular plates with fl:t surface, '/I(to 1 inch thick, inches long, I/% to 2 inches wide
I/?
to 6
6 8 10 19 14 R O D D I A M E T E R , OPNDTHS I N C H
16
Effect of Change in Electrode Diameter on Intensity Ratios
Column 1 lists the number of the Xational Bureau of Standards chemical chip standard corresponding to the core rolled to prepare the spectrographic standard listed in column 2. The certified value for manganese in the chemical standard is given in column 3, values redetermined chemically on the core sample in column 4, and the spectrographic value read from the smooth curve through all points in column 5. The average deviations of the spectrographic homogeneity determinations (50 to 70 runs) are given in column 6, and the certified values for the spectrographic rod standards are given in the last column. I n one case, standard 404,the homogeneity determinations showed a high average deviation, and this standard was not certified for manganese. Standard 414, which was specially prepared by the Ford Motor Co., exhibited the highest homogeneity of the lot. Renewals of depleted standards are now prepared directly by rolling billets rather than employing the core samples.
ANALYTICAL CHEMISTRY
ISSO It was later found necessary to test proposed standards for radial as acll as longitudinal segregation, particularly in the case of manganese which tends to concentrate in the center line of the ingot. In a subsequent preparation of a high-manganese standard (Nos. 405a and 805a, 1.90% manganese) by the Carnegie Steel Co. it was considered advisable to roll a flat slab and t o cut out the center section by automatic torch in order t o ensure uniform distribution of manganese. The two remaining parts nere rolled and ground t o the standard rod sizes, 7/32- and 0.5-inch diameters, and were found t o show a high order of uniformity. .-""I
L I N E PAIR
-
.ZOO
If, in a n unusual instance, disagreement is observed, further checks may be necessary t o uncover a cause, such as incorrect concentration value, interference in the spectra, or possibly physical difference between the standards. For example, the results obtained for a set of steel standards for manganese are shown in Figure 3. The deviations of points at the lower end of the curve from the smooth curve are sufficient t o require investigation to determine an error that might be involved. The preparation of nonferrous standards is complicated by the need for many types to match the composition of the wide variety of commercial alloj-s and by the tendency of these alloys to segregate. The outstanding work on nonferrous standards was carried out by the Aluminum Co. of America, which has made more than 200 aluminum standard samples available to the general public. These standards bvere prepared originally by casting and rolling a large heat to size (2.5-inch dismeter) or, in small lots, by casting in a mold. It was found necessary with these alloys t o specify a limited area of homogeneous metal t o be used in sparking the standard. I n cooperative preparation of four KBS aluminum alloy standards, homogeneity tests in this laboratory shon ed excellent homogeneity in a ring area between 0.625 and 1.125 inch from the center of the 2.5-inch disk as shown for the determination of magnesium (Figure 4). I
1.45
,-
Figure 3.
Table 111. Homogeneity Tests on 7/32-Inch Rods of HighSpeed Tool Steels Steel Heat KO. la
lb Radial
la Ib
Linear
3
Mn 0.8 1.4 1.5
8.80
1.2 1.3 Radial 3 1.8 4 2.6 a Values considered excessive. 4
I
I
-
I
I
I
I
I
7
I
8 8
a
Analytical Curve for Rlanganese
High-alloy steels offer a greater problem in obtaining uniform metal. Tests made on rods prepared by rolling cores from NBS standards showed poor homogeneity, and it was considered necessary t o prepare special heats of steels for the purpose. Results of homogeneity tests on a trial set of high-speed tool steels prepared from cores are shown in Table 111. Tests for radial segregation in sample l b show exceseive deviations for manganese, chromium, and vanadium. The radial segregation test is very sensitive and is designed to show any possible indication of difference across the radius. I n the test sharp cones (60" included angle) are cut on center of the rod and near the edge and these are sparked as for the linear homogeneity tests.
Test Linear
I
Average Deviation, yo Si Cr V 1.5 0.8 0.8 1.7 1.6 3.0 0.7 0 0.6 1.8 4.W 9.0a 1.2 0.9 1.0 1.7 1.6 1.2 0 1.8 3.1 0.4
2.4
2.0
W 1.8
..
0.6 5.3 5.9
&Io
.. .. .. ..
4.9
1.0 1.7
8.3a
0.3
3.0
1.6
Following the satisfactory demonetration of homogeneity, the standards are analyzed preferably by several laboratories. When the results are compared and values assigned to the composition, the final test of the standards is to employ them t o plot analytical curves for spectrographic analysis. This may be termed a "consistency test." If, in comparison with a group of Ptandards, the new standard falls on the smooth analytical curve, additional assurance is obtained that the assigned composition is correct.
I25L
1201
o
I
I
i/a
2/0
I 3/0
I
4/a
I 5/a
I
I
7/a
6/a
DISTANCE FROM C E N T E R
IN
I
wa
l 9/a
wa
INCHES
Figure 4. Results of Homogeneity Tests for Magnesium in a No. 21s Aluminum Alloy Standard The homogeneity tests were made using a low-energy, critically damped spark which attacked only a small area of the sample, of the order of a 0.12binch circle. The discharge was produced by a n Applied Research Laboratories' multisource unit with 5 microfarads' capacitance, 400 microhenries' inductance, 10 ohms' resistance, and the sample polarity positive. The variation in magnesium, showing not only greater inhomogeneity toward the center but also a general decrease in concentration, is observed also for other constituents in the alloy. .4 recent improvement in the production of standards a t the Aluminum Co. involves the direct progressive chilling of the molten metal as it is poured t o obtain n casting of highly uniform composition. This procedure may offer promise in the preparation of other types of nonferrous alloys, particularly where application t o the analysis of chill-cast analytical samples is desired. The recent preparation of a set of five NBS tin metal standards in rod form will serve as a n example of the planning involved in the testing of the metal for homogeneity and in the final analysis of the standards by both chemical and spectrographic methods. Details of the preparation of the standards will be given elsewhere ( 7 ) . The standards have the composition given in Tabl(t IV.
1551
V O L U M E 2 3 , NO. 11, NOVEMBER 1 9 5 1 Table IV.
Composition of NBS Spectrographic Tin Standards (Per cent) Standard XumberO 432 or 433 or 434 or 832 833 834 0.097 0.056 0.019 0.094 0.055 0,022 0.075 0,047 0,019 0.095 0.019 0.050 0.020 0.0095 0.0044 0,0046 0,020 0,0095 0,0095 0.0065 0.0018 0,0098 0.0052 0.0020 0.0096 0.0053 0.0020 0.011 0,0045 0.0020
431 or 831 0.20 0.19 0.16 0.19 0.038 0.041 0,015 0.020
Element Copper Lead Arsenic Antimony h-ickel Zinc Silver Bismuth Cadmium Cobalt
0.020
0.021
436 or 835 0,0077 0.015 0.0090 0.010 0.0024 0.0020 0.0010 0.0011 0.0011 0.0011
Rods of 400 series are 0.25 inch in diameter, 4 inches long; 800 series 0 . 5 inch in diameter, 2 inches long. 0
Table V.
Homogeneity Test for Copper in NBS Standard Sample 432 Plates
Castings 1
I 0.422Ta
2
3
4 5
6 7 8
I11
I1
0.417B 0.417T
0.443T
. 0.403T
0.439B 0.444T
9
10 11 12 13 14 15 16 17 18
0.420B
IV 0.381B
0.441B
0.383T 0.409B 0.386B 0.409T 0.386T 0.408B
0.421T
0,384B
0.440T 0.409T 0.423B
0.438B
0.382T 0.405B
V 0.421B 0.418T 0.416B 0.415T 0.414B 0.417T
VI 0.373B 0.369T 0.367B 0.368T 0.367B
occur in low ranges of concentration (less than 0.50/0) and are present in proportions not usually found in samples submitted for chemical analysis. Chemical determinations are difficult under these conditions and, for several of the very low values, are considered unreliable. Spectrochemical analyses of the tin specimens were attempted by a procedure in which the sample is converted to oxide, and the arc spectra are compared with those of oxide standards synthesized from pure metals and solutions. The procedure is essentially that described by the American Society for Testing Materials ( 1 ) . Results obtained by cooperating laboratories ( 7 ) showed good agreement, indicating that procedures of this type may prove advantageous as a general tool for determining minor elements in standard samples. However, experience with the analyses of the tin standards has shovin that attention t o a few simple rules is essential in realizing high accuracy. The recommendations are as follows: Analyses of the standards should not be attempted until their homogeneity has been demonstrated. Representative portions of the metal specimens should be prepared by milling or turning and the sample should be well mixed t o ensure that each cooperator receives a representative sample. An approximate analysis should be furnished t o each analyst. The analyst selects or devises a method n.hich permits analysis of the sample relative t o standards synthesized through preparation of solutions. The method may involve excitation of the sample in solution, salt, or oxide forms. Each synthesized standard should be made to match its corresponding sample as closely as possible in general composition and in the elements t o be determined. standards and samples should be prepared a t the same time and all details of the procedure handled in the same manner. Each sample should be compared directly with its matching synthetic standard on the same plate using reproducible excitation.
0.366T
Sumerical values are log intensity ratios of Cu 2824.37 t o Sn 3223.57. T represents determination a t top of casting and B a t bottom.
Each standard was prepared in the form of 18 castings having four legs about 12 inches long and slightly tapering t o 0.5-inch diameter a t thc lower end. The rods were rolled t o 0.5 inch or 0.25 inch in diameter. Final tests were considered necessary to demonstrate the homogeneity of the metal and to ensure proper identification of the pieces. At this point careful planning is necessary t o obtain the maximum amount of information with the minimum labor. The tests made m r e designed t o uncover significant random inhomogeneity, progressive drift in composition from the first t o the last casting, and any difference between top and bottom of the castings. The tests were made by spark spectral analysis (6) using the step sector t o obtain lines a t optimum densities for photometric measurement.
-4limitation involved in this method lay in the fact that only six spectra could be photographed on a single plate and considerable shifts were observed between plates. The system observed in testing a standard is shown in the results for copper in standard B given in Table V. In this plan six castings are tested on a pair of plates, the tops and bottoms being alternated betrveen the two plates for successive castings. Six plates suffice for testing the 18 castings in the manner shown. An array of this kind is particularly well adapted to statistical study, for example, by analysis of variance. The results of the st,udies indicated that there was no significant random or positional variation in composition among the castings, and representative portions were prepared for analysis by cooperating laboratories. ANALYSIS OF STANDARDS
Standards in the past have been analyzed almost exclusively by chemical methods. However, in the case of the tin standards and others in preparation in this laboratory many of the elements
The precaution of preparing samples and standards a t the same time is advisable because oxides or salts map change in thrir excitation behavior after standing a few weeks. The close matching of pairs of standards and samplesin composition provides for similar behavior in arc excitation. Furthermore, photometric errors are minimized, because the problem reduces essentially t o the observation of any slight difference bet\yeen spectral lines of nearly equal intensities. Comparison of sample and standard on the same plate is essential t o avoid errors from shifts between plates. The procedure may be outlined in general terms for the analysis of samples A, B, and C, having graded concentrations of minor constituents ranging from high in sample A t o low in sample C. Standard samples -4’, B‘, and C’ are prepared to match A, B, and C closely in composition on the basis of preliminary rough analysis. An additional standard at each end of the range serves to establish the analytical curve and a hlank is carried through t o detect any contamination. Thus the follon ing pieparations Tvould be made: Sample
-4 B
C
Synthesized Standard
H’ (high range)
A ’ (to match sample A ) B‘ (to match sample R) C’ (to match sample C) L’ (low range) X (blank)
Analytical curves are estahlished from nieasurements of intensity ratios obtained on three or more runs of the sets of synthetic standards and blank. If the blank shows a significant impurity level, corrections are made to the concentrations in the standards. Each sample is analyzed by running it a t least in triplicate rvith the corresponding synthetic standard having the same number of runs and on the same plate or film. A large number of runs on the sample may not be necessary, but an equal number of runs $hould be made on the sample and its correspond-
ANALYTICAL CHEMISTRY
1552 Table VI.
Spectrographic Determination of Copper in NBS Tin Standards
No. of Standard
Deterininations of Copper 0.178
43 1
0.186 0.180
432
Av. 0.181 0.095 0.097 0.088
Deviation from Mean
Standard“ Deviation
of Variationb
Coefficient
0,0042
2.3
0.0047
5.05
0.003 0,005 0.001
0.002 0.004 0.005
Av. 0.093
mum electrode shape. arc current, and other factors, this source may be used satisfactorily. As a n example, the results on the spectrographic determination of copper in the NBS tin standards are given in Table VI, in which the average coefficient of variation of the mean corresponds to 1.75% of the amount determined. The agreement of two cooperating laboratories employing similar procedures in the analysis of the tin standards confirmed the precision obtainable] as is shown in Table VII.
Table VII. Comparison of Results of Analysis of Tin Standards by Two Spectrographic Laboratories Label of Standard 0.0187 0.0185
434
435
0.0183 Av. 0.0185 0,0077 0.0073 0.0080
Element Copper
0.0002 0.0
0.0002 1.08
0,0020 0.0 0.0004
Arsenic
0.0003
Av. 0.0077
0.00035 Av. coefficient of variation Av. coefficient of variation of means of three runs
Standard deviation, u =
Lead
dz
4 55
3 03 1 75
where d is deviation of indiridiial re-
Laboratory
431
: A
0,181 0.180
B .1
Antimony
B .1
Cadmium
.I
B
432 0,093
433 0.054
434 0,0185
4
r
0.0186
0,0077 6.0077 0.0148
0.056
0.0220 0.0220
0.079
0.048 0.046
0.0194 0.0195
0,0150 0.0090 0.0090
0,092
0,0517
0.0197
0.0102
0,192 0.192
0.093
0.054 0.053
0,091
0 160
0.078
0.163 0.188 0.188
0,092
0.092
0.052
0.0196 0.0108 0.0203 0.0097 0.0054 0.00209 0.00108 0,0210 0.0098 0.0055 0.00200 0.00108
B
sult f r o m mean a n d n number of determinations. b Coefficient of variation Y = 2 where C i s concentration.
l0OC
ing standard. T h e analytical exposures in this case would have the following arrangement: Plate 1
Plate 2
Plate 3
A
B
C
’ 4
R
c
B B’ B’
C
I
B‘
C‘
C‘
Similar results have been obtained in the spectrographic anrtlysis of stainless steel standards, and the indications are that other standard samples, both chemical and spectrographic, ma)- be analyzed satisfactorily for minor conqtituents by procedures of this type. ACKNOW LEDGM EIIT
The authors gratefully acknowledge the assistance of Martin
B. Cavanagh in making measurements referred t o in this paper.
C’
I n order to check the accuracy of preparation of the synthetic Ptandarde the operation should be repeated with new preparations of samples and standards. For purposes of statistical analysis of cooperative tests all individual determinations should be reported and results should be given t o one digit beyond that considered significant. Rounding off can be done when the final averages are calculated. Details should be provided by cooperators on the method employed, including details of sample and etandard preparations, of excitation, and of photometric measurement. The accuracy obtainable by procedures of this type depends, of course, on the reproducibility of the spectral excitation. Esritation by the direct current arc may be necessary in order to detect and determine trace elements. By the addition of a buffer such as graphite t o the sample and by the choice of opti-
LITERATURE CITED
(1) Am. Soc. Testing Materials, Philadelphia, Pa., “Methods of Chemical Analysis of Metals,” Tentative Method E51-43,T pp. 442-4. 1950. (2) ChuAhiil, H. V., and Churchill, J. R., IND.ENG.CEEM.,ANAL. ED.,17, 751 (1945). (3) Corliss, C. H., Ed., “Report on Standard Samples for Spectrochemical Analysis, 1950,” Tech. Pub. 58B, Philadelphia, Pa., American Socicty for Testing Materials, 1950. Bur. Stand(4) Corliss, C. H., and Scribner, B. F., J. Research ~ V a t L ards, 36, 351 (1946). (5) Jensen, D. P., Chris, G. J., and Toung, J. F., “Spectrochemical Analysis of Copper Alloys” in “Suggested Methods for Spectro-
chemical Analysis,” Philadelphia, Pa., American Society for Testing Materials, in press. (6) Scribner, B. F., J. Research Natl. Bur. Standards, 28, 165 (1942). (7) Scribner, B. F., and Cavanagh, hf. B., Ibid., in preparation. RECEKEDOctober 1. 1951.
