V O L U M E 26, NO. 5, M A Y 1 9 5 4
909
PERCENT OF TOTAL COUNTS DUE TO HOLMIUM
dysprosium with little interference from holmium. The calculated error inadysprosium determination caused by varying amounts of holmium is plotted in Figure 3. CONCLUSIONS
This work has shown that europium can be determined in the presence of samarium, and dysprosium in the presence of holmium more readily by actiEu-Srn MIXTURE vation analysis techniques usDy-He MIXTURE ing appropriate bombardment times than by spectrophotometry. Other rare earth elements (excluding lutecium) mill PERCENT OF TOTAL COUNTS DUE TO SAMARIUM cause less than 1% error in Figure 3. Counting Rate Error Introduced by Low Cross-Section Component in Actithese activation determinations vation Analysis of Europiiiiii-Samari~imand Dysprosium-Holmium 3lixtures if present in amounts equal t o or less than that of the euroIrradiation time. Eu-Sm, 9.2 hours; also 1 hour Dy-Ho, 2.4 hours pium or dysprosium. It has Total sample weight 100 m g . been shown t h a t equal amounts of lutecium nould into the deterniinatioii of europium in :I sample containing equal cause a n error of about 5% in the determinations. amounts of samarium and europiuni. Figure 3 shows this error This type of analysis can be used very e a d y for folloming a calrulated for different niistures of the two elements. The process for separating rare earths, such as an ion exchange experimental results verified there calculations. The data preseparation. I n addition, this method can supplement the sented in this figure are dependent upon rariables such as sample Ppectrophotonietric method of analysis for rare earth elements thickness, length of irradiation, cro.-s-section value, and counting such as tl\-qproeium and europium. equipment used, hut give a good indication of the limits of the method. LITERATURE CITED 1Iaxinium sensitivity for the europium determination in the presence of sanimium is obtained for irradiations of the order (1) H o l l a n d e r . J. l f . , Perlnian, I., a n d Seaborg, G . T., Table of Isotopes, U n i v e r s i t y of California R a d i a t i o n L a b o r a t o r y R e p o r t , of 9 hours, a1t)hough shorter irradiation times can be used as shon-n UCRL-1928 revised, December 1952; Rm. M o d . Phys., 25, in Figure 3 with Fatisfactory results. K i t h the shorter irradia469 (1 953). tion time, however, 1e.s activity is obtained and the probable ( 2 ) H u g h e s , D. J., et al., S e u t r o n Cross Sections. U.8. Atomic E n e r g y error indicated in Figure 2 for the determination would be inC o n i m . , AECU 2040 (May 15, 1952); AECU 2040 Supplement 1 ( S o v . 20, 1952); AECU 2040, S u p p l e m e n t 2 ( J u n e 15, creased. Various inert (to activation analysis at this flux level) 1953). materials could lie present in the samples described in Figure 3 (3) X e i n k e , W. IT,, a n d .knderson, R . E., .\NAL. CKEM.,25, 778 but self-absorption effects must be considered if the sample (1953). weight exceeds .revera1 hundred milligrams. (4) Jloeller. T., a n d R r a n t l y , J. C . Ibid.,22,433 (1950). DYSPROSIUY . ~ S D HOLXIIX In the spectrophotometric (5) R o d d e n , C. J . , 6.Rescarclt S a t l . Bur. Standards, 26, 557 (1941). determination of dysprosium a t 910 1 1 1 ~holmium makes some (6) Ibid., 28, 265 (1942). contribution, but by taking readings at. two wave lengths and RECEIVEDfor review Soveniber 2 i , 1933. . I c c e p t e d January 28, 19*54. using simultaneous equations, the amounts of each can be deterThis work u-as generously supported by a grant from the Michigan Memorial niined. .kctivation anal~-sis permit. the determination of Plioenix Project.
-
---
High-Frequency Titration of Micro Quantities of Chloride and Sulfate GEORGE S. BlEN Scripps lnstitution of Oceanography, University o f California, La lolla, Calif.
-4
8 O S E method of studying the shalh1\- marine sediments of
the northern Gulf of Mexico, chloride and sulfate ions are being determined in the interstitial water. Some restriction 011 t h terhnique ~ re~ultsfrom the samples being often as small as 0.3 or 0.4 ml. in which the total quantities of chloride and sulfate do not exceed 5 and 1 mg., respectively. Furthermore, as the water is often muddy, the usual turbidimetric metbods of analysis are impractical. T h e titration of sulfate n-ith the help of a high-frequency or;cillator has been found successful for quantities of sulfate as
low a9 0.5 m g . (4). The method is geneially applicable for precipitation titrations. Jensen ( 2 ) titrated for the chloride in potassium chloride by using silver nitrate and silver acetate solutions and compared the end points. H e found that silver acetate gave a much qharpei end point. Jensen and Parrack (3) also found that the sharpness of the end points depends on the “nonpolarity” of the solvent. For some titrations, they used benzene with enough methanol t o maintain solubility and found much sharper end points. -411 these results indicate that reduced degrees of dissociation bring about sharper end points.
ANALYTICAL CHEMISTRY
910 Silver acetate and barium acetate have been wed as precipitating agents in the series of expeiiments to be described. The dielectric constant of the solvent, water, was lowered by various proportions of dioxane, which was chosen for this purpose because it has a dielectric constant as low as benzene and is miscible Nith water in all proportions. The author has been able to determine quantities as low as 0.5 & 0.01 mg. of chloiide and 0.15 =J= 0.003 mg. of sulfate nith a mavimum variation of 2% b e h e e n duplicate runs. Since the precipitants do not interfere with each other, it was possible to determine sulfate and chloride ions one after the other in the same sample and in the same titration cell. APPARATL S A h D RE iGEYTS
A Model V chemical oscillometer manufactured by E. H. Sargent and Co. was used for the titrations. Four titration cells with approximately the same cell constants were supplied i ~ i t h the instrument. Specially constructed syringe-type micropipets, calibrated to the desired volume, were used for pipetting the samples, and Gilmont ultramicroburets were used for the titrations. rill reagents used in this series of experiments were Baker analyzed quality with the evception of dioxane, which was technical grade, and silver acetate, which n?as prepared in this laboratory.
AD/AV is zero. Take the data of run I1 in Tahle I, and let V be x and AD/AF' be g; then,
x1 = 0.100 and r2 = 0.110 and yl = -300 and
~2
=
400
Substituting t h e v vnlueq into the usual for mula ror a straight line: (r
- 0.lOOj '(0.100
- 0,110) = ( g - 3001 '( -300 - 400)
Solving for z for z./ = 0. one obtains point.
Table 1.
D
3V
1111
of 0 0 3 2 8 3 5 H290r s o h )
-
AD'AV
AD
2'2,783 22,783 22,786 3 300 Vol. a t end point, ml. 0 1040 Norniality Ba(CzHaO?)? 0.1408 Variation from gravitnetric data (0.1403.Y~. yoo.21
0.090 0.100 0.110
0.1043, tr-hich in the end
Standardization of Barium kcetate by Oscillometer
(Against 0 2772 Run I
V
5 =
0.01 0.01 0.01
28,120 28,117
-5%:
-1;
D
23.121
R u n I1 AD AD AV -10 -1,000 -3 -300 400 0.1043 0.1404
0.07
PROCEDURES
Standardization and Calibrations. A11 volumetric apparatus was calibrated by weighing the water delivered. The pipets were found to have a maximum variation of 10.20/,. The total capacity of the Gilmont ultramicroburets was 1.0000 i 0.0001 ml. in each case. Sulfuric acid was standardized acidimetrically against sodium borate decahydrate as a primary standard. Silver acetate solutions were standardized against potassium chloride by the Vohr method, and barium acetate solutions was standardized gravimetrically. Analytical Procedure. About 0.3 ml. of the sample was accurately pipetted with a calibrated pipet into a flask and diluted with water, A drop of methyl red indicator was added to the solution, which was then acidified with 0.1N acetic acid and heated to boiling. After cooling to room temperature, it was transferred to a titration cell and 40 ml. of dioxane was added. Enough water (about 60 ml.) was added to bring the level in the cell to half an inch above the metal ring of the cell and then a drop a t a time was added until the dial reading was brought up to betn-een 600 to 700 units, so that a titration could be completed by turning the dial alone while no changes of the setting of the switches on the left would be necessary. For sulfate, seeding the precipitate with barium sulfate crystals has been recommended (1, 4);this was found unnecessary.
RESULTS
Barium acetate solution was first standardized by a gravimetric method and then checked with the oscillometer by titrating against standard sulfuric acid. The end points of these titrations were calculated algebraically according to the method described. The data pertinent to the cnlculation are shown in Table I.
in 2 0
C U R V E S O F SO4' A N D G I ' B Y 8 0 1 5 7 0 2 ~ A N DAP c2n302 S U C C E S S I V E L Y
5 0 0 b , p fTITRATION
c_ 3 z >
2
ON T H E O S C I L L O M E T E R 0
001
002
I S A M P L E OF I N T E R S T I T I A L W A T E R 2 0 , 4 0 0 \ ( o1 8 4 3 ~ ) ~ ~ - F R O M B C - 2 1 8 - 5 2 , 2 5 - 2 6 c m l MI
RolCZH30J1\
,
I
C.iLCUL.kTION OF END POINT
The usual method of obtaining the end point with a Model 1 ' oscillometer has been t'o plot the dial readings which relate the dielectric constant of the solution to the volume of reagent used. The end point is obtained graphically from either one of the three possibilities: a true minimum point,, the intersection of two curveg, and an inflection point. The case of the end point occurring a t an inflection point may be disregarded because by using the proper ratio of dioxane-water mixture, a minimum point can usually be obtained. Sometimes the titration curves are so steep that the end point is really the intersection of two curves. I n these cases one may assume that the intersection point is the minimum of a continuous curve. Unless very accurate results are necessary, it is generally sufficient to assume the minimum point exists. For a minimum point, AD/AV is zero. If AD/AV is plotted as a function of V , the portion of the curve between the points where AD/AV changes from negative to positive assumes a straight line. By means of the regular algebraic formula for a straight line, one can Rimply calculate the value of V7 for which
1
I 20,000
1
I
I 0 5
0
MI
ne czn,02
I
10
1 5
2 3
(004257~1
Figure 1. Typical Titration Curve
Silver acetate solution waq fii st standardiLed against weighed amounts of potassium chloi ide by the Llohr titration method. A standard potassium chloiide solution was used as the sample and titrated with the silvei acetate solution by uqing the oscillometer. Portions of 0.2772 nil. of 0.4763S potassium chloride solution were titrated aiitl .I cninpxiiqon of the results is given in Table 11.
V O L U M E 26, N O . 5, M A Y 1 9 5 4
911
s h o m in Table 111, indicate acceptable accuracy to as low a sulfate content as 0.15 mg. When the sulfate content is lower than 0.1 mg. the method is not sensitive enough. The difficulty, however, can be overcome by adding a definite volume of a sodium sulfate solution corresponding to a definite volume of the standard barium acetate solution and then titrating to the end point. The sulfate content was calculated from the difference between the total volume of acetate used and the volume equivalent to the sulfate added. .4 t>-pical titration curve is shown in Figure 1.
Table 11. Standardizatioii of Silver Acetate by Oscillometer Compared with JIohr Method (Xorniality of silver acetate soln = 0 05342A-) I I1 Run number 2.41 2.42 1-olume a t end point. nil. 0.05354 0.05332 Sorniality iZgCnHjO9 soln. 0,23 0.20 T-ariation f r o m M o h r method. Yo
Table 111. Analysis of Sea Water s04-I’iesent, 11g .
c1-
SO4 - -
round, IIg.
E r r o r , $7c 0.49
Present, Mg.
c1-
Found, 1Ig.
4 063 4.063
4.068
4.080 4.076
1.35
4.063 4.063 1.339 1 339 1 072 1 072
...
0.5838
0.80 0.40
1.2 0.22 0.71 0.41
1.69
1.079
4.012
Error, yo 0 10 1.4 0.50 0.40
1 341
0.15
1.336 1.073 1.074 1.070 0.5360
0.22 0.10
0.19 0.19
0.19
.4 sen-water sample having a chlorinity of 18.59 parts per thousand and a sulfate content of 2.56 parts per thousand --as analyzed by the procedure prescribed. More dilute sample. of known chloride and sulfate contents n-ere prepared by diluting the standard sea water nnd analyzing as before. The results,
ACKNOWLEDGMENT
The author is grateful to Sorris W.Rakestraw for suggesting the uqe of the oscillometer in this work. LITERATURE CITED (1) d n d e r s o n , L. J., a n d Revelle, R. R., ISD. ENG.CHEM.,;IXAL. ED.,19,264 (194T). ( 2 ) J e n s e n , F. IT.,Ibid., 18, 599 (1946). (3) J e n s e n , F. Y., a n d P a r r a c k , A. L.. Ibid., 18, 595 (1946). (4) J l i l n e , 0. I.. =ISAL. CHEM..24, 1247 (1952). RECEIVEDfor review July 29, 1953. Accepted January 2 8 . 1 9 j 4 . Contribution from the Scripps Institution of Oceanography, S e w Series, No. 691. This work is a part of the Anlerican Petroleum Institute Research Project 5 1 .
Determination of Bismuth in Pure Bismuth-Lead Eutectic Alloy Improved Phosphate Method LOUIS SILVERMAN and MARY SHIDELER Atomic Energy Research Department, North American Aviation, lnc., Downey, Calif.
B
I S l I U T H finds use as a constituent of alloys of low melting point. I t is frequently alloyed n i t h lead, cadmium, tin, and antimony, singly or in groups ( I ) . These alloys are generally of use in the solid state, but considerable engineering effort is being put forth to use alloys of low melting point as liquid coolants and heat transfer agents (6). In thi. connection extended corrosion studies, both static and dynamic, have been made for these Ion- melting alloy.. If the binary alloy bismuth-lead (55.5 to 44.5% by weight) is to be studied, a method for chemical analysis must be available to check the new mateiial as well as the alloy after it has been subjected to corrosion testing. Determination of either constituent would be satisfactory; the bismuth procedure was chosen. Many methods have been reported for the determination of traces of hisniuth (8, 1 2 ) and for small amounts of bismuth (3, 5, 11), a
