Mass Spectrometric Determination of Lead in Manganese Nodules TSAIHWA J. CHOW and CHARLES R. McKlNNEY Division o f Geological Sciences, California lnstitute o f Technology, Pasadena, Calif.
b Chemical and mass spectrometric procedures were developed for the determination of the isotopic composition and concentration of lead in manganese nodules. Contamination and memory studies are described in detail. A statistical treatment of the d a t a was based on the fact that properly recorded spectrometer d a t a were shown t o b e normally distributed. The best values for the lead atom ratios in CIT (California Institute of Technology) shelf standard No. 1 are given as well as the isotopic composition and concentration of lead in a suite of Pacific Ocean manganese nodules.
M
are found on the floors of the oceans (11). These nodules are concentric concretions of manganese and iron oxides ( I ) and contain appreciable amounts of lead which have been deposited from sea water (4). The lead in manganese nodules is considered representative of oceanic lead (4, 10) and a study of its isotopic composition may provide evidence concerning the formation of the earth’s crust ( 9 ) . The present investigation was undertaken to develop a method for determining the isotopic composition and the concentration of lmd in manganese nodules using isotopic dilution techniques and a surface ionization source mass spectrometer. ANGANESE KODULES
PREPARATION OF TRACER
The lead tracer. enriched in lead-206, i r x s provided by 11,G. Inghram of the
University of Chicago. This lead was chemically isolated as the metal from a uranium ore obtained from the Eldorado mining district of Canada. After chemical analysis shoned it 99.99% pure, the metallic lead iras dissolved in nitric acid to make up a standard solution containing 0.6172 gram of lead per liter. The isotopic composition of this tracer was 0.06, 88.24, 8.78, and 2.92 atom % ’ for lead-204, lead-206, lead-207, and lead-208, respectively.
Organic solvents and nitric and perchloric acids were doubly distilled under reduced pressure. Ammonium hydroxide and hydrochloric acid irere prepared by passing t h e respective gases through filters into distilled m t e r in ice-cooled polyethylene bottles. The water n a s distilled four times. and in the fourth distillation, entrained liquid was removed from the yapor phase by passing it through a superheater containing silicon carbide. Reagent blanks were determined periodically with the lead tracer and found to contain less than 0.02 y of lead per amounts of chemicals used in one normal determination. Borosilicate glassnare was estimated to introduce no more than 0.1 y of lead per analysis. However, to minimize contamination from borosilicate glass, Teflon beakers (made by machining white bar stock) were employed in evaporating acid solutions rather than the commercial molded beakers which contain graphite. Special precautions viere taken in cleaning the apparatus ( I S ) . Significant amounts of lead contamination originate from the air; hence the following control measures were applied. Lead-laden dusts and aerosols were removed from the laboratory air by electrostatic precipitation and filtration; laboratory floors were flushed with m t e r twice a week and gelatin step pads were placed a t the laboratory entrances ; glassware and solutions were covered with “parafilm”; and solutions being heated and evaporated Irere enclosed in borosilicate glass or Teflon containers (Figures 1 and 2) I\ hich were continuously flushed with filtered nitrogen.
Table
Beaker Teflon
Borosilicate glass
Chemical Procedure. Remove visible clay and foreign material from t h e manganese nodules. Grind t h e sample t o a fine powder in a n agate mortar and dry a t 115’ C. t o constant w i g h t . To 0.2 gram of sample, add 15 nil. of concentrated hydrochloric
Lead Contamination from Air
Condition Open Sitrogen-flushed container Open Nitrogen-flushed container
EXPERIMENTAL
Contamination. All chemicals used in this study were analytical grade and were purified b y extraction with dithizone and/or recrystallization.
I.
The results of experiments conducted to determine the magnitude of lead contamination from the air are reported in Table I. I n these experiments, 500 ml. of 6W hydrochloric acid were introduced into the beakers and then 30 y of lead-206 tracer were added. The beakers containing this solution were taken to dryness in various environments in the time period listed in the table. The amount of lead contamination vias calculated from the change in the isotopic composition of the tracer, assuming that the contamination was modern common lead. The evaporations performed in the ordinary-air laboratory were in a Transite hood recently coated with Tygon paint. It was concluded that the amount of lead deposited in the open beaker was two or three times greater than that in the beaker in the nitrogen-flushed borosilicate glass container. This was true for both the ordinary- and purifiedair laboratories. It was also s h o m that air-borne contamination from ordinary air exceeded that from the purified-air laboratory by a factor of 10. The nitrogen-flushed borosilicate glass container alone will not eliminate the airborne contamination. Lead contamination deposited in an open beaker in ordinary air exceeded that from the nitrogen-flushed borosilicate glass container in the purifiedair laboratory by a factor of 20 or 30.
Nitrogen-flushed container
Laboratory Ordinal)-
Time, Days 8
iiniount of
Ordinar>-
8
1.13
Pure air Pure air
8 8
0.44 0.18
Pure air Pure air
1 1
0.02 0.03
VOL. 30 NO. 9, SEPTEMBER 1958
Lead,
y
4.07 2.32
0.13
1499
Made from sld. 4-liter b e a k e r
1
5' t i l t
3 p o s t s , equally s p a c e d , one i s short
z_L
- - - --- ------____ --
J
4
Made from std. 3-literbeaker
Condensate drain 'EEL
-
Flushinq g a s inlet
Figure 2.
J
Figure 1.
Borosilicate glass evaporator tank and cover
a n d 5 ml. of nitric acid. Heat t o boiling until t h e evolution of chlorine gas ceases. Cool the solution and centrifuge off t h e insoluble residue. Rinse the residue and retain the rinsings. Evaporate the solution to dryness a t 125' C. to dehydrate the silica. Dissolve the baked residue in 30 ml. of 3N hydrochloric acid by warming briefly and then cooling. Centrifuge off the silica. Dilute the resulting solution to 50 ml. in a volumetric flask. T o a 10-ml. aliquot, add 30 y of lead206 tracer for determining the lead concentration. Isolate the lead from the remaining 40 ml. of solution for determining the isotopic composition. Evaporate the solution until sirupy and add 30 ml. of concentrated nitric acid. Heat just to boiling and add 1.5 grams of potassiuni chlorate, a little at a time, waiting until the effervescence ceases before adding the next portion. Boil until yellowish fumes from the decomposition of the chlorate are no longer evolved. Nanganese dioxide separates as a fine brownish black precipitate. Cool the solution and centrifuge off the manganese dioxide. Evaporate the nitric acid solution to dryness. Dissolve the residue in 20 ml. of 6.5-4' hydrochloric acid. Shake with 20 ml. of diethyl ether for 2 minutes. Discard the ether phase which contains ferric chloride. Evaporate the aqueous layer to dryness and repeat the ether extraction to ensure the complete removal of iron. Evaporate the hydrochloric acid to moist cake. Add 5 ml. of 25% ammonium citrate solution and transfer the solution to a 125-ml. separatory funnel. Adjust the p H of the solution to 9 with ammonium hydroxide solution. Shake vigorously with 20 nil. of 0.002% dithizone in chloroform for 2 minutes. Draw off the chloroform layer into another separatory funnel, extracting the aqueous solution n-ith other portions of dithizone, adding these extracts to the first. The last extraction should show no reddish color of lead dithizonate. Shake the chloroform extract with 10 ml. of 1 to 100 nitric acid
1500
ANALYTICAL CHEMISTRY
solution to decompose the lead dithizonate. Transfer the aqueous solution which contains lead t o a separatory funnel and add 2 ml. of 1% potassium cyanide solution. Adjust the p H to 9. Add 5 ml. of chloroform and sufficient dithizone powder t o complex all the lead. Shake for 2 minutes and allow the two phases t o separate. Then evaporate the chloroform layer to dryness in a 5-ml. beaker. Add 1 ml. each of concentrated nitric and perchloric acids, and evaporate the solution to dryness a t 220" C. to destroy the organic matter. The white residue is lead chloride. I n a 1-ml. centrifuge tube, add 10 mg. of amnioniuni nitrate in 0.5 ml. of ivater. The p H of this solution should be about 3 or 4. Rinse out the lead chloride residue from the beaker with this solution using a capillary pipet. Transfer the solution to the centrifuge tube, pass filtered hydrogen sulfide into the solution until the lead sulfide precipitate coagulates, and then centrifuge. Fill the capillary pipet with about 10 y of lead sulfide together with 10 pl, of solution. Allow the lead sulfide to settle to the pipet tip and eject the lead sulfide, together with about 5 11. of solution, onto the surface of the tantalum filament. Evaporate the solution to dryness in open air by heating the filament with a current of about 1 ampere until the ammonium nitrate fuses. The sample is now ready to be mounted in the mass spectrometer. An alternative procedure for smaller samples might be the dissolution of the lead chloride in ammonium sulfate and the evaporation of this solution directly on the filament.
Mass Spectrometer. The mass spectrometer was a 60-degree sector single focusing instrument with a 12inch radius of curvature, constructed a t Caltech from a modified design of h1. G. Inghram of t h e University of Chicago. A detailed description is
Teflon evaporator tank and cover
t o be published elsewhere by C. R. McKinney (8). The ion source and collector nere housed in stainless steel chambers and were accessible by removing gasketed covers. The gaskets were made of pure silver and the vacuum-tight joint was achieved by means of a tongue and groove arrangement similar to that described by Walcher (24). By carefully tightening the flange bolts, the gaskets were re-used 40 to 50 times. The ion source (6) was operated to produce ions with a 5-k.e.v. energy. Although the source was constructed for multiple filament operation, only the center or ionization filament was used for the analysis of lead. Singly charged lead ions were produced Iiy thermal ionization of lead sulfide deposited on a tantalum filament (12). During the initial heating in the rnass spectrometer, lead sulfide was probably oxidized to lead sulfate, which is helieved to be the source of lead ions. The ions which arrived a t the collector passed through a 50% transmittance grid, through an externally adjustable defining slit, and finally impinged upon the conversion dynode of an electron multiplier. Entrance apertures were designed so that the signal produced by the grid was proportional to the sum of the intensities of the four lead ion beams. Because of difficulties in suppressing and/or collecting secondary electrons produced on the grid wires, the grid signal was not only a function of the ion beam intensity but also was dependent upon the position of the ion beam upon the grid. Nevertheless, the grid signal was used as a partial basis for evaluating ion beam stability. The grid signal was produced by passing the collected ion current through a 10"ohm resistor which was connected to the input of a n Applied Physics vibrating reed electrometer. The resolved ion beams impinged upon the conversion dynode of an electron multiplier operated to have a gain of about 900. The electron current produced in the multiplier mas passed through a 2 X 109-oh1n resistor connected across the input of a vibrating reed electrometer. Experience shon ed that acceptable datn could be collected if the least abundant lead-204 ion
current arriving a t the conversion dynode would produce a signal equal to or greater than 3 mv. across the 2 X 109ohm resistor. For common lead with a 204 abundance of 1.5%, the signal of 3 mv. was equivalent to a total ion ampere current of about 3 X arriving a t the grid. The output of the two vibrating reeds was connected to a dual pen strip chart recorder for simultaneous recording of the grid and collector signals. The range switches on the electrometers were on a 1-2-5-10 system to permit as large a pen deflection as possible consistent with a reasonable number of switching steps. I n the analysis of manganese nodule lead, which approximates modern common lead, it was possible to record the four ion beams between 60 and &O% of full scale This was attempted in all the analyses. The total lvidth of the resolved ion beam was shown to be approximately 0.013 inch, \+hich was about one fourth the mass dispersion in the lead region. K i t h the collector defining slit set a t 0.025 inch, flat-topped peaks were obtained. K i t h a uniforni scanning rate, about equaI time would be spent on the top of the peak and in the valley between the peaks. K'ormally, however, the scanning rate between peaks was accelerated to conserve the sample. At the standard operating pressure of mm. of mercury, the contribution of a given ion beam to an adjacent ion beam was less than 1 part in 1000 of the given beam. The electronics were considerably modified from those of Inghram, and the magnetic scanning circuit changes, in particular, have resulted in improved performance. A multiturn coil was placrd in the air gap of the analyzer magnet and n-as connected to a servo.cystem hich performed the function of changing the magnet current to induce a constant voltage in the coil. Over a limited mass range this resulted in a constant time rate of change of mass. The servo-system also was capable of changing the magnet current rapidly, so that a hen the direction of scan was reversed, the effect of the tail of the magnetic hysteresis loop upon the peak shape was eliminated.
Spectrometer Operation. Dried helium was admitted t o the mass spectrometer from a storage reservoir filled t o a predetermined pressure, such t h a t when the reservoir and spectrometer vacuum system were connected, the net pressure of helium n as slightly greater than atmospheric. The ion source was located at the lower end of the vertically
mounted analyzer tube and, in this position, it was possible to remove the cover from the source and have the analyzer tube remain filled with dried helium. The sample changing operation required about 10 minutes; approximately 1.5 hours were required to establish the operating pressure of 10-6 mm. of mercury. The filament temperature was raised by slowly increasing the current to about 0.5 ampere. After the loss of water and the decomposition of the ammonium nitrate, the filament current was slowly raised to approximately 1.2 amperes corresponding to a temperature of about 950" C. a t the center of the l/zinch long tantalum filament. Data were recorded when the following minimal conditions were satisfied: The minimum total ion current arriving a t the grid was 3 X ampere; the drift rate of the ion current was less than 0.25y0 per minute; short term intensity fluctuations in the ion current were less than 27,; the analyzer tube pressure was less than 10-6 mm. of mercury. Normally a t least 40 sets of intensity determinations were recorded by cyclical scanning over the four ion beams. Source Memory. Memory was considered t o exist when lead or lead compounds, deposited around the source slits from previous runs, m-ere so located t h a t they could contribute ions to those being produced from the sample. It was postulated t h a t this material would be vaporized and diffuse to the filament where it would be ionized. If ions were produced directly from the slits, they would not have the proper energy for collection a t the same position as ions of the same mass originating on the filament. Where there are two isotopically different materials producing ions, the ratio of the current due t o isotope i to that due to isotope j can be shown to be
Table II.
PbNe tracer Av. Pacific manganese nodule CIT shelf std. No. l a Modern common lead (Shoshone Plateau basalt)
Component Pbae tracer CIT shelf std. S o . 1
Component CIT shelf std. No. 1 Pbme tracer
+
~
For a n acceptable memory, K will be of the order of or and for the case where b , < a,, the above reduces to dRij = a,bi - a,b, dK a?
This ratio, defined as p , is a measure of the sensitivity of a particular isotope ratio to change by a memory component. For the case in point, manganese nodule lead, CIT shelf standard No. 1, and the lead-206 tracer are subject to intermixing. The composition of these leads and modern common lead (3) is listed in Table 11. The values of p in Table 111 were computed for the normally reported ratios for two conditions: when the major component was the lead-206 tracer to which a small amount of CIT shelf standard No. 1 was added; and for the inverse condition. The ratios and values for using manganese nodule lead will not be appreciably different. For the first condition, b, was not less than a,, and therefore, p was evaluated As can be for K = 10-3 and seen, these values are not appreciably different. The most sensitive ratio was not used because of the difficulties in making an accurate determination of the low abundance of lead-204. The next most sensitive Pb206'208 ratio was used to evaluate the memory. At the completion of a run, the fila-
Atom Per Cent Pb Pb207
Pb ?08
0.06 1 35 1 44
88.24 25 24 23 92
8.78 21 08 22 28
2.92 52 32 52 37
1.38
24 94
21 27
52 42
Obtained from Johnson, Matthey, and Co. Limited quantity available for diatribution.
Memory Sensitivity pb206I204
llemory
dRij = aibi - aibj dK ( a i KbiY
Isotopic Composition of Various Leads
Pbz04
Table 111. Major
where K = N B / N a , N a is the amount of substance A , and ad is the atom per cent of isotope i in substance A . Similar definitions hold for N B and bi from substance B. It can be seen that
K
Isotope Ratio 1470
10 -3
16.6
P
- 3 . 5 X lo4 - 3 . 3 x 104 60.7
Pb 206' 2 O i Isotope Ratio 10 1 1.1
VOL. 30,
Pb 206'2O8 Isotope Ratio
P
-22 8 -- 2 2 . 7 3.5
NO. 9,
30 2 0.5
SEPTEMBER 1958
P
-532 -514 1.7
1501
5 amperes for about 2 hours. The
These ratios were considered to be identical as the difference betryeen them was less than the sum of the standard deviations. One can show that K -
w2 a&, - a&,
- pa&,
nhere p is the difference between the ratios and, in this case, had a maximum value of 0.21. Using the appropriate values for the isotopic abundances, the maximum value of K mas found t o be 4 X Given proper operating conditions, memory less than this amount has been negligible for the purposes of this investigation. DATA ANALYSIS
The drift rate of the intensity of successive peaks of the same mass over a t least three sets of peaks was established by visual estimation. Within each sct of peaks, using the appropriate drift rate, the intensity of the peaks at masses 204, 207, and 208 was interpolated to the middle of the peak a t mass 206. These interpolated intensiTable IV.
Date of KO.of -4nalysis Ratios 1 10/20/56 34 2 10/22/56 37 3 10/24/56 20 4 10/25/56 45 5 10/28/56 44 6 10/31/56 46 11/ 1/56 48 11/ 2/56 45 9 11/11/56 48 10 11/16/56 40 Grand mean Std. dev. of grand mean 3 5 in yc of grand mean
Run No.
A
I074
ties minus the electrical zero were used to calculate the ratios 206/204, 2061207, and 2061208 for each set. The application of the appropriate scale factor, scale factor correction, and a velocity discrimination factor to the means of these ratios gave the corrected atom ratios for the run. Electrometer scale factor calibration was performed a t tJyo-week intervals over a period of one year. These calibrations showed no trend with time and thus the mean ITas applied to the year’s analyses. As has been summarized by Inghram and Hayden ( 7 ) , secondary electron production on the conversion dynode of a n electron multiplier is a function, among other things, of the velocity and mass of the impinging ion. The quantitative aspects of these two factors in the mass spectrometer were evaluated by Choiv and Patterson ( 2 ) using an isotopic mixture technique, details of \Thich will be reported elsewhere. It was found, as reported by others (Y), that the application of a correction equal to the square root of the mass
Isotopic Analysis of CIT Shelf Standard No. 1
E
204 16 65 16,675 16.62 16 67 16 59 16 64 16.69 16 64 16 64 16 60 16 64 0 015 0 090
1.073
206a 208 0 4561 0.4560 0.4575 0.45635 0.4569 0.4562 0.4563 0.4567 0.45705 0.4571 0.4566
0.0007
0.0003
0.065
0.07
206~ __
Q
0.06
0.03 0 05
0 0 0 0 0 0 0
05 04 06 04
05 05
06
207 1.073 1.072 1 074 1 072
1 0735 1 073 1 072 1 073 1 074 1 073
~
Q
0.003 0.002 0.003 0.002 0.002 0.002 0.002 0.002 0.002 0.003
For Single Run
(1
Average std. dev. 0 049 Average std. dev. in $To of grand mean 0 29 Maximum std. dev. in 70of grand mean 0.36 Corrected atom ratio.
1502
ANALYTICAL CHEMISTRY
0.0023
0.0011
0.21
0.24
0.28
0.33
Q
0.0015 0 0010 0.0012 0.0012 0.0011
0.0008
0.0010 0.0011 0.0009 0.0009
ratio was justified. Such a correction was used in these data. DETERMINATION OF STANDARD LEAD
A section of a bar of spectrographically pure lead metal (CIT shelf standard KO. 1) n-as dissolved and used as a source of lead to test the reproducibility of analysis by the mass spectrometer. The results of a series of ten runs extending over a period of almost one month are given in Table IT. The corrected atom ratios reported for each run n-cre calculated, as described, after the rejection of those values which satisfied Chauvenet’s criterion (15). Often there was experimental evidence for rejection, in that some of the rejected values were recorded immediately f o l i o ~ i n ga change in ion current. I n yiem of the considerable supeistructure that has been established for the treatment of normally distributed data, the chi-square test ryas used to evaluate quantitatively the closeness of fit of the 2061’208 data to a normal distribution. The class interval for the chi-square test was set a t 0.001 nhen using the uncorrected atom ratios. From the results given in Table I-, it mas concluded that the 206,’208 data fit a normal distribution quite well. The test for skewness, d z d i d not shorn a n y significant trend; however, the distribution of the data does appear to be somewhat flatter than a normal distribution, as 7 of the values of p2 are less than 3. From the homogeneity of the data, among other things, it was reasonable to assume that the 2061204 and 2061207 data were also normally distributed. The data for run 9, together with the fitted normal frequency distribution curves, are shov-n in Figure 3. The grand mean (16) was computed from the means of each run with a k value of 4. The grand mean coniputed with a k value of 1 was not appreciably different. These are believed to be the best values for the lead atom
Table
1 -
V.
Normal Distribution Tests on 2061208 Data”
33 _. 27
0.20
+0.74
3.14
14 i j O:52 i 0 . 2 5 2.20 6 . 9 19 0.99 -0.36 1.35 20 19 0.40 -0.01 2.09 5 9 . 5 13 0.73 -0.26 1.58 6 10.6 11 0.52 -0.53 3.06 7 6 . 9 15 0.96 -0.87 1.96 8 8 . 3 13 0.80 +0.21 2.25 9 19.8 11 0.04 +0.14 4 . 4 7 10 8 . 1 13 0.83 -0.18 2.12 If a hypothesis completely specifies the frequencies .fc to be expected in n classes, the goodness of fit of a sample providing frequencies can be tested by calculating chi square, x2 = z ( j o- fc)z/fo. n’ is the number of groups selected less the number of imposed conditions. Px2 is the chi-square probability for goodness of fit of a sample distribution as a function of x2 and n . The third moment, A = Z(z - ;)3/ nu3, is a measure of the sken-ness of the data relative to the normal distribution. For a strictly normal distribution z/is; = 2 3 4
5
0.
The fourth moment, p, = Z ( r - 2)4/ no4,is a measure of the flatness of the data relative to the normal distribution. For a strictly normal distribution & = 3.
ratios in the C I T shelf standard KO. 1. A tabulation of the properties of t h e errors in a single run are also given a t the bottom of Table IV. The assigned percentage error for each of the 3 ratios I\ as believed to be the maximum expected if the established operating conditions for the mass spectrometer \\ere satisfied and if the data were shown to be normally distributed. -4statistical basis for the comparison of the analjses of different samples or thc analyses of the same sample by different laboratories was believed t o have been established. RESULTS A N D DISCUSSION
.
The results of the analyses of 16 Pacific Ocean manganese nodules are give in Table VI. The nodules had a n average moisture content of 157,. The concentration of lead in these nodules approximates the determination made by Goldberg (j), although his results may h a r e been systematically lower than those reported here. The large sample size, the high lead concentration in these nodules, and the esisting contamination levels precluded any effect of contamination on these data. The analyses denoted by the letter d were made prior to the establishment of the spectrometer operating conditions. These four analyses have a mean
Table VI.
Lead Concentration and Isotopic Composition of Pacific Ocean Manganese Nodules
Specimen“ Horizon nodule MP-43-A
hIP-25-F2 MP-37-C
206c Pb,b __ P.P.M. 204 1120 18 63 (18 63 2050 18 74 2180 2080
MP-33-K
1940
LIP-5 core 2 Chubasco (34-92) \IP-26-A3 GA-3dredge7 hIP-43D LIP-3section11 MP-3 section 3 Henderson nodule Jasper PAS-19121 Wigwam-5
2090 27
2440 1500 1680 980 720
206c 207
2060 __
208 0.4828 0 03 1 193 0,001 0 0 7 ) d ( 1 192 0,007)d (0.4797 0.48265 0 03 1 1935 0.002 (18 70 0 13)d (1 194 0,007)d (0,4787 0.4802 18 68 0 04 1 194 0.002 0.4806 18 70 0 03 1 194 0.002 (18.72 0.17)d (1.196 0.009)d (0,4806 0.4822 18.71 0.03 1.195 0,002 0.007)d 10.4817 (1.197 (18.70 0 09)d , . 0.4811 1.195 0.002 18.71 0.04 0,4804 18.69 0.05 1.196 0.003 0.4823 1.197 0.002 18.625 0.05 0.4838 1.197 0.002 18.63 0.03 0.4831 1.198 0.003 18.73 0.05 0.4832 1.198 0.002 18.68 0.03 1.199 0.003 0 ,4833 18.67 0.05 U
1910 18.76 0.04 1.199 1.201 1180 18.76 0.05 1.201 1000 18.66 0.04 1,203 576 18.64 0.05 Same from Scripps Institution of Oceanography. * Concentration in dried material. c Corrected atom ratios. d Old analysis. See text for explanation.
I 7
0.002 0.002 0.003 0.003
U
0.0008 0.0039)d 0.0008 0 . 0032)d 0.0007
0.0009 0 .0045)d
0.0009 0.0030)d 0.0008 0.0014 0.0009 0,0008 0.0014 0.0008
0.0015
0.48185 0.4828 0.4842
0.0011
0.4836
0.0010
0.0010 0.0009
0
deviation 3 to 5 times greater than those 11-hich n-ere run after February 1957. This clearly demonstrates the improvement in the data that resulted from the use of the spectrometer operating conditions as outlined. The isotopic composition of RIP-25-F2 in Table VI was different from that reported by Patterson et al. (IO) in that the present analysis showed lead-206 to be 1.1% less abundant and lead-208 to be 0.657, more abundant. The geocheniical significance of the isotopic composition of lead in manganese nodules will be discussed elsewhere. ACKNOWLEDGMENI
The authors wish to express their appreciation for many invaluable suggestions received from C. C. Patterson. They are also indebted to E. D. Goldberg and Robert Rex of the Scripps Institution of Oceanographj- of the University of California a t La Jolla for providing the manganese nodules. The critical review of this paper by G. J. Rasserburg is gratefully acknowledged. LITERATURE CITED
(1) Buser, W.,Gruetter, A., Schweiz. mineral. petrog. Mitt. 36, 49 (1956). (2) Chow, T. J., Patterson, C. C., unpublished material.
(3) F a d . Henry, “Suclear Geology,” p. 290, Kilep, New York, 1954. ( 4 ) Goldberg, E. D., J . Geol. 62, 249 (19.54’1. \ - - - - I
( 5 ) Goldberg, E. D., Scripps Institution of Oceanography! La Jolla, Calif.,
personal communication.
(6) Inghram, AT. G., Chupka, IT. ,4., Rec. Sei. Inst?. 24. 518 11953).
( 7 ) Tnghram, 11.G., Hapden, R. J., .Yatl. Rcsearch Council S a t l . Acad. Sei. ( U . L ‘ ~ .Kuclear ), Scz Ser. Rept. Yo. 14
(1954). (8) h:cKinney, C. R., unpublished material. (9) Patterson, C. C., Geochim. et Cosmochzm. d c t a 10, 230 (1956). (10) Patterson, C. C., Goldberg, E. D., Inghram, 11.G., Bull. Geol. Soc. Anier. 64,1387 (1953). (111 Pettersson, Hans, Goteborgs Kyl. T- efenskaps-Vitterhets-Samhall.
Handl.
Ser. 2 , S o . 8 (1943). (12) Tilton, G. R., Sicolaysen, I,. O., Geochim. et Cosmochim. Acta 1 1 , 28 (1957). (13) Tilton, G. R., Patterson, C. C., Brown, H. S., Inghram, M. G., Hayden, R. J.. Hew. D. C.. Larson. E. S.. Bull. Geol. So;. - 4 u i e r . 66, 1131 (1955). ’ (14) Walcher, IT-.) S a t l . Bureau Stcls. C m . Yo. 522, 272 (1953). (15) Korthing, il. G Geffner, J., “Treatment of Experimental Data,” p. 197, Wiler, Sew I-ork, 1943. ~
RECEIVED for revieir December 11, 1957. ,.4ccepted April 12, 1958. Contribution A-0. 85C, Division of Geological Sciences, California Institute of Technology, Paeadena, Calif. Work supported by American Petroleum Institute Project S o . 53 and the U. S. Atomic Energy Commission Contract -4T( 11-1)-208.
VOL. 30, NO. 9,
SEPTEMBER 1958
1503
