Table 111. Suitability of D.M.E. of Teflon for Showing Diffusion Control of Pb" Reaction PbfZ
e
Test solution. 1.0ni.If PbC1, in 1M HCI t , 3.24 seca m, 2.20 mg./sec.a P b n c k , 1.54 CITI." (di/dt)m,x h l / l j (di/dt),,,,, cm.'/2 pa./nun.
h,* em.
X 86
78 5
9 9 10 10 11
87 0 95 0 103 5 111 5 121 5 a
b
29 75 18 56 03
h'/z pa./min.
cm.-'/z
.i7.0
60 0
63 5 66 5 69 5 73 8
6.43 6 46 6 51 6 53 6 58 6 69
113 em. Corrected for P b a c k .
At h
=
time. This equation is the one used to correct for the back pressure of a glass capillary (5). Relation of Concentration, C, of Reducible Ion, Pb+*, to Diffusion Current, (id), and to Peak Height, (dildt) max, of First-Derivative Wave.
Plots were made of C us.
i d
and of C
us. (di/dt)max. In each case, the relation
is linear and the line passes through the origin. The data thus shon that I t is possible with the D.M.E. of Teflon to make quantitative polarographic nieasurements of C from plots of C us. either i d or (di,'dt),,,ax. ACKNOWLEDGMENT
Grateful acknowledgment is made to
P. F. Thomason, who supervised this study, and to I). J. Fisher, IT.L. I M e a , and R.Jf-. Stelzner for the advice they generously gave during the course of it.
LITERATURE CITED
(1) Belew, W. L., Analyt,ical Chemistry IXvision, Oak Ridge Kational Laboratory, Oak Ridge, Tenn., unpublished data. (2) Belew, W.L., Itaaen, H. P., J . Electroanal,. ('hem., 8, 4 i 5 (1964). (3) Brezina, LI., Zurnan, P., "Polarography in LIedicine, Biochemistry, and Pharmacy," p. 11, Interscience, Kew York, 1938. (4) Ibid., p. 735. ( 5 ) Kolthoff, I. M., Lingane, J. J., "Polarography," 2nd ed., 1-01, I, p. 86, Interscience, S e w York, 1952. (6) Ibid., p. 194. i i ' i Ibid.. 1-01. 11. D. 529. ( S j Lingane, J. i.,J . Am. Chem. SOC. 61, 2099 (1939). (9) Raaen, H. P., AXAL. CHEM. 3 6 , 2120 (1964). RECEIVED for revieF September 23, 1964. Accepted February 17, 1965. Research sponsored by the L-. S. Atomic Energy Commission under contract with the Union Carbide Corp.
High-Sensitivity Controlled-Potential Coulometric Titrator Controlled-Potential Coulometric Determination of Milli- a n d Microgram Quantities of Uranium a n d Iron H. C. JONES, W. D. SHULTS, and J. M. DALE Analyfical Chemisfry Division, Oak Ridge National Laborafory, Oak Ridge, Tenn.
b An instrument has been built specifically for the potentiostatic coulometric determination of small amounts (-0.010 to TOO peq.) of materials. Emphasis was placed on careful construction using unmodified amplifiers and conventional circuitry. Precise calibration circuitry i s incorporated into the instrument for convenience and also to provide a source of easily adjusted constant current for other electroanalytical applications. The instrument has been tested with and used for the determination of milli- and microgram quantities of iron and uranium over a period of several years. The procedures used for these determinations involve both reversible and irreversible systems, the use of either mercury or platinum as the controlled electrode, and both reduction and oxidation electrolyses. They are therefore representative of the procedures that are most often encountered in controlled - potential coulometry. This paper describes the instrument and procedures, and it presents typical analytical results.
I
i w m t year+. several electronic in\tiuiiicnt. that can be used for conti olled-l)otential coulometi I C analy-1. hnvc h e n de-crihed (1-6, 9, flN
680
ANALYTICAL CHEMISTRY
I S ) . Generally, these instruments have been designed and used for the determination of quantities of about 500 l e q . and up. The instrument described in this paper, designated ORKL Model Q-2564, was built specifically for the determination of sniall amounts of materials having large equivalent wightsthat is, for quantities of about 0.01 to about 100 l e q . The instrument is designed to be simple, stable, and easily maintained. Accordingly, t,he chassis layout and construction are inade carefully, with particular emphasis on the elimination of ground loops and switching transients. Provision is inade for internal absolute calibration of the integrator in coulombs per readout volt. (The internal calibration current may be used externally for other electroanalytical applications.) The principle of control of potential and of integration of cell current used in this instrument is essentially the same as that' described by 13ooman (1) and was selected for thip application because of its simplicity, espected ease of maintenance, and because the three G.IP/R ( I O ) US.1-3 chopper-stabilized operational amplifiers do not have to be modified in any way. Current amplifying stages are omitted. One G.IP/R R-10013 power supply furnishes the
regulated *300 volts d.c. necessary for the amplifiers. .I block diagram of the instrument is presented in Figure 1; a complete circuit diagram is presented in Figure 2 . DESCRIPTION OF INSTRUMENT
Current Amplifier. .-is seen in the block diagram (Figure l ) , one of the amplifiers ( S o . 2 ) i q used both as a control amplifier and current amplifier. .-implifier No. 2 maintains the controlled electrode, which is connected directly to the input of the amplifier, a t virtual ground potential. Because the total cell current flows through one of the microequivalent range resistors in the feedback path of amplifier KO. 2 , the voltage developed at the output of this amplifier is proportional to the cell current. This voltage is used as an input signal for amplifier No. 3, the integrating amplifier. Control Amplifier. The input of amplifier KO. 1 sees the difference between the control potential and the potential of the controlled electrode with respect to the reference electrode. .implifier To. 1 forces this difference t o be essentially zero by maintaining the counter electrode a t such a potential t h a t , by current
feedback through the electrochemical cell, the potential of the controlled electrode with respect to the reference electrode is equal to the control potential. The control potential is the potential selected for the desired electrorhemical reaction. The maximum cell current available from amplifiers KO, 1 and 2 is approximately =k8 ma. and is c.ntirely adequate for the present application. If greater current capability is desired, another version of this instrument could be constructed using a solid state amplifier such as the G.$P/R SI'656. The current capability of the 81'656 is about 20 ma. The heat dishipated by the SP656 is also much less than that dissipated by the US;\-3, and the SP656 should require less maintenance. Integrator. Amplifier Xo. 3 is connected as a time integrator. The high quality capacitor (Stabelex D , Industrial Condenser Corp., Chicago, Ill.) inserted in the feedback network of amplifier E o . 3 stores a n electrical charge-the charge flows from the output of amplifier S o . 2 through a 4megohm resistor into the input of amplifier No. 3-that is directly proportional to the tirile integral of the cell current. Hence. the output voltage of amplifier S o . 3 is a measure of that integral. The sensitivity of the integrator circuit is determined by the magnitude of the feedback resistor in amplifier E o . 2 circuit. This integrator circuit is extremely stable-e.g., the voltage on the capacitor will change less than 10 mv. in 15 minutes with 50 volts d.c. on the capacitor (-0.02% change), provided the amplifier bias is properly adjusted. Control Potential Supply. T h e con trol potential is supplied by a full wave bridge rectifier circuit operating from a 117-volt, 30-ma. isolation transformer. T h e transformer (Elcor Isoformer Model KO. XX120-30T, Elcor, Inc., Falls Church, Va.) was selected for its low interwinding capacitance. This minimizes the insertion of 60 c.p.s. and its harmonics into the control circuitry. The output of the bridge rectifier is well filtered and Zener diode regulated a t about 5.4 volts d.c.. X portion of this voltage is selected as the control potential by a Helipot. Sensitivity and Readout Provisions. Either of four sensitivity ranges (0 to 1, 0 to 10, 0 to 50, and 0 to 100 peq.) can be selected by switching resistors in the feedback loop of amplifier S o . 2. The cell current passing through the selected feedback resistor produces a lroltage a t the output of amplifier No. 2 which in turn causes a current to flow through a 4-megohm resistor into the input of the integrating amplifier. The output of the integrating amplifier is connected to two voltage dividers: one feeds an appropriate readout device
I EFERENCE /CMIITROL
ECTRODE
1
CONTROLLED CURRENT RANGE
WTENTIAL
*1.
D
ITOMATIC
E \----
M E T E R 0 RELAY
GAP/R USA-3
CONTROL AMPLIFIER
ZENER SUPPLY CONTROLLED POTENTIAL
imo/v Zma'v
?TROLLED
CURRENT
Olmolv
-
--
p Eq. RANGE
-vA
100
7
.
RESET
-50
10
I/
-1
RECORDER
~~
# 2 . CONTROL AND
# 3 INTEGRATOR
CURRENT A M P L I F I E R
Figure 1 .
High-sensitivity coulometric titrator,
(such as a Honeywell Pointerlite Potentiometer, Heiland Division, Honeywell. Denver, Colo.) and the other feeds a standard 10-mv. Brown recorder. Recorder readout is provided to make possible better interpretation of the integrator output and/or graphical correction for background currents a t high sensitivities. Readout switching is discussed in a following section. Calibration. T h e instrument is calibrated absolutely in coulombs (passed through the cell) per volt of readout. Calibration is achieved by operating the instrument in the cons t a n t current mode (see below) so t h a t the number of coulombs passed through the cell circuit can be calculated from the current magnitude and t h e time required to attain a suitable integrator readout voltage. The number of coulombs passed is then divided by the integrator readout voltage to give the electrical calibration factor, f:
f
=
it -
V
coulombs/volt
where
i
RUBICON POINTERLITE POTENTIOMETER
AMPLIFIER
magnitude of constant current, amperes t = time, seconds V = integrator readout voltage, volts =
Although the microequivalent ranges are exact multiples (10.05%) of each other, utmost accuracy requires individual calibration of each sensitivity range. Constant Current Mode. T h e constant current mode used in the cal-
ORNL Model (2-2564
ibration procedure is obtained by switching precision resistors (calibrated to k0.05y0) between the controlled electrode lead and the reference electrode lead. For instrument calibration the cell leads are removed from the cell, and the reference electrode lead and the counter electrode lead are connected together externally to complete the circuit. The above procedure causes the potential selected by the control potential dial to be impressed across any one of the four precision resistors available. The readout device is switched to read this potent'ial and thereby give an accurate indication of the current. The four current ranges are 0.1, 1, 2, and 5 ma. per volt. This constant current is also available between the reference electrode lead and the counter electrode lead for 11urposes other than calibration. Automatic Cut-Off and Current M e t e r Protection. The cell current meter, with lower-limit contacts for automatic cut-off, is provided with four ranges (50 pa.) 500 pa., 5 ma., 50 ma.). Each range has meter protection furnished by a shunt diode. .\ resistot. is placed in series with the curyent meter and current range switch on each range. The resistance is selected to cause the shunt diode to begin carrying an appreciable amount of the cell current a t and above full scale on the meter. The error in the current mpter reading is approximately 2y0 of full srak at full scale on the meter. The Ioiver-limit meter contacts are used to switch ~iower to a double pole relay having normally closed contacts that complete the reference electrode and counter elec.ttmlr VOL. 37, NO. 6, M A Y 1965
681
i tlll Ill
I L
682
ANALYTICAL CHEMISTRY
4 Figure 2. Circuit diagram, high-sensitivity coulometric titrator, ORNL Model
Q-2564
circuits. When actuated, the relay opens these leads to the cell thereby terminating the electrolysis. Readout Switching. T h e control amplifiers and integrating amplifier are capable of operating with either output, polarity without switching. A reduce-oxidize switch reverses t h e cell current meter, readout' device, and recorder connections. Switching is provided for connecting the readout device to a n y one of the five following places: the full output of the Yo. 2 amplifier, for adjustment of the amplifier bias; the full output of the integrating amplifier, for adjustment of the amplifier bias; a voltage divider on the output of the integrating amplifier, for observing accurately a voltage proportional to the charge on the integrating capacitor; across the per cent span potentiometer for calibration of the per cent span dial; or across any one of the precision resist,ors used in the constant current mode, for obtaining an accurate measurement of the constant current. Construction Details and Checkout. Careful wiring is practiced throughout this instrument,. Each amplifier and its associated circuitry has a separate ground bus returned to the common tie point in the R-IOOB power supply. I n addition, all a x . leads are shielded to minimize pickup. All rotary switches are standard size with ceramic insulation. A 5-ampere circuit breaker is used as a master power switch for the instrument. h p plication of 1 3 0 0 volts d.c. to the amplifiers is autoniatically delayed by a I-minute time-delay relay. A checkout and test procedure, ORNL ST-260, and a trouble shooting guide have been prepared and are available from the authors, for those who may wish to construct the instrument. EXPERIMENTAL EVALUATION
T o evaluate the performance of this instrument and to test the innovations incorporated into it, a thorough study of two controlled-potential coulometric titration procedures was made: the reduction of uranyl ion in 0.5F H2SO4a t a mercury pool electrode and the reduction-reoxidation of iron in 1F HC104 a t a Idatinurn gauze electrode. These two titrations are of particular practical interest a t ORNL; they are also representative of reversible and irreversible systems, require the use of both the mercury and the platinum electrode, and involve both reduction and oxidation electrolyses. Accordingly, they are typical of types of procedures that are often encountered in coulo-
metric titrimetry. This study then was designed to evaluate not only the performance of the instrument but also the procedures themselves (precision, accuracy, limit of detection) over the entire working range of the instrument and to establish which types of background corrections are necessary and how they are best applied. Because of the diversity of the two procedures that were studied, the results obtained should be generally indicative of the results that are to be expected of other controlled-potentia1 coulometric titrations involving small amounts of electroactive materials. Apparatus. Titration cells of two different sizes were used in this study. T h e basic design a n d pertinent dimensions are given in Figure 3 . The larger cell accommodated either a mercury pool or a platinum gauze controlled electrode and was operated with solution volumes of about 10 ml. in either case. When the mercury pool (7 to 8 ml. of Hg) mas used as the controlled electrode, the stirrer was located a t the mercury-solution interface and positioned to give maximum stirring of the solution and mercury surface without splashing; the stirrer was driven by an 1800-r.p.m. constant speed motor. Two 3/8-inch 0.d. Vycor tubes with unfired bottoms (No. 7930 glass, Corning Glass Works, Toledo, Ohio) were used as low resistance (100 ohms or less) salt bridges with negligibly small solution leakage. Each tube contained 0.5F H2S04. One contained an 8-inch length of 16-gauge platinum wire as counter electrode and the other contained a saturated calomel reference electrode (No. 39270, Beckman Instruments, Inc., Fullerton, Calif.). The mercury that was used as the controlled electrode for uranium titrations had been distilled once under vacuum and rinsed once with 0.5F H2S04 before admission to the cell. Finally, oxygen was sparged from all solutions before electrolysis and all electrolyses were made under a n oxygenfree atmosphere. High-purity (99.9%) nitrogen gas was used for that purpose and was further purified before entering the titration vessel by passage through two scrubbing towers that contained CrS04 solution and through one that contained 0.5F H2S04solution. Under these conditions, the ultimate current level attained at -0.325 volt us. S.C.E. was 5 to 10 pa. Under the conditions employed for the iron titration-a platinum gauze controlled electrode in the larger cell with 1 F HC104 as the medium-the final current levels were 8 pa. a t f0.295 volt us. S.C.E. (reduction) and 1 pa. a t +0.656 volt vs. S.C.E. (oxidation). The smaller cell (dimensions are given in Figure 3) was operated with 2 ml. of solution and 2 ml. of mercury. To minimize the occurrence of the reaction 2.M
+ 02 + 2HzS04 2-llS04
+ 2H20
where d l represents mercury or im-
purities in the mercury, the solution was sparged 5 minutes before the addition of mercury to the cell. For the same reason, the mercury was not rinsed with sulfuric acid solution prior to use. Sparging was continued 5 minutes after addit'ion of the mercury before prereducing the solution. High purity argon ( O . O O O l ~ o 0 2 ) was brought to the cell through an all-metal tubing system (to prevent diffusion of oxygen into the argon stream) and used as sparge gas without further purification. Reproducible background currents of 0.5 pa. were attainable. The stirring action caused a small amount of liquid to be entrapped under the mercury, until this problem was eliminated by making a small indentation in the bottom center of the weighing bottle. No titrations that utilized a platinum electrode were made in the smaller cell. Preparation of Standard Solutions. Standard uranyl sulfate solutions were prepared to contain U+6 a t concentration levels of 7 to 8 mg. per ml. in 0.5F H2S04; they were prepared from National Bureau of Standards primary standard U308 and also from highpurity (99.95%) uranium metal. Standard ferric perchlorate solutions were prepared from high-purity (99.94%) iron wire to contain Fe+3 a t a concentration level of 3 to 4 mg. per ml. in 1F HC104. Quantitative dilutions were then made, in 0.5F HzS04and I F HC104, respectively, to obtain less concentrated standard solutions of U+6 or Fe+3 as required for the titrations in the large coulometric cell. These dilutions were of such magnitude that sample test portions of 1000 pl. could be taken a t every concentration level that was studied. All pipetting was done at 20" 0.1' C. with calibrated micropipets (1000 pl.). For work with the small cell, special standard solutions of -50 pg. per ml. of U f 6 in 0.5F &So4 were prepared from 99.95% uranium metal and stored in polyethylene bottles. Test portions of the standard solution were weighed for analysis. The total uncertainty in the amount of uranium in a 1000-pl. test portion of the standard solution was calculated to be less than *O.l%. This included the uncertainties in the weighing of the uranium metal, dilution, measurement of the density of the solution, and final weighing of the test portion. As the test portion became smaller, the uncertainty in the amount of uranium taken progressively increased because of the increase in the uncertainty of the final weighing step, The uncertainty was still less than +0.4% for a 50-J. test portion that contained -2 pg. of uranium. Procedural Details. Performance d a t a were collected a t the 67-, 6.7-, 0.7-, 0.07-and 0.007- peq. levels to include the entire working range of the instrument. This was done by making a series of titrations of iron and of uranium a t each level in the larger cell. The iron titrations were made in 1P HCIOa medium a t a platinum electrode: reduction a t +0.295 volt vs. S.C.E. and coulometric reoxidation at f0.655 volt us. S.C.E. All uranium titrations were VOL. 37, NO. 6, MAY 1965
683
made in 0.5F H&04 medium a t a stirred mercury pool electrode. Two series of uranium titrations were run in the larger cell a t each level. I n the first series, a prereduction was made at +0.075 volt us. S.C.E. and then coulometric reduction of Ut6 to Ut4 was made at -0.325 volt us. S.C.E. These potentials are based upon the polarographic half-wave potential (-0.125 volt us. S.C.E.) for the reduction of uranium in 0.5F I n the second series of uranium titrations, the prereduction was made at f0.160 volt us. S.C.E. and the uranium reduction was made at -0.200 volt us. S.C.E. These latter potentials are based upon the coulogram for this reduction-i.e., a plot of integrated current or readout voltage us. zerocurrent electrode potential, a t various stages during the electrolysis. Finally, a series of uranium titrations was run a t the 0.4- and the 0.02-peq. levels in the smaller cell utilizing the most sensitive instrument settings. For these series, prereduction was made a t 0 volt us. S.C.E. and coulometric reduction of C+6 to U + 4 was made a t -0.250 volt us. S.C.E. Data were taken during these several series such that a comparison could be made between the results obtained by the potentiometer and recorder readout.
Table I.
RESULTS
Titration of Uranium, Large Cell. When 8 mg. or so (-67 peq.) of uranium were titrated, the current, limited a t 8.2 ma. initially, remained constant for approximately 15 minutes and then decreased exponentially with time to a constant value of 5 to 10 pa. Total electrolysis time was 20 minutes when U6 was reduced a t -0.325 volt us. S.C.E., and 25 minutes when U+6 was reduced a t -0.200 volt us. S.C.E. The precision was excellent a t this level, the relative standard deviation for a single observation being 0.1%. h slight positive bias was observed when standard UOzS04 solutions that had been prepared from LT308were used, but no bias was detected when the standard solutions were prepared from 99.95% uranium metal. Use of the recorder as readout device and extrapolation of the readout voltage back to zero time gave results that were 0.1 to 0.2% lower than those obtained when the potentiometer was used as readout device (after terminating the electrolysis a t 50-pa. current). This difference occurs because the graphical readout technique corrects for the continuous background current (5 to 10 pa. in the larger cell), while the
Results of Titration of U+6 in 0.5F H2S04, 8-rng. Level
Prereduction potential, +0.075 volt us. S.C.E. Reduction potential, -0.325 volt us. S.C.E. Blank correction, none. Solution volume, 10 ml. Results based on Results based on recorder potentiometer readout when readout, extrapolated to z = 50pa t = O Found, Error, Found, Error, Taken, mg. % 8, % mg. m6. % 8, 70 0.1 7.981 (0.1 7 982 8 006 +O 3 0 1 7 630 7 654 +O 3 0 1 larch 3, 1965. Research Sponsored by Y,S. Atomic Energy Commission under contract with 1,:nion Carbide Corp.
EIements
Application to Purification and Radiochemical Determination of Berkelium FLETCHER L. MOORE and W. THOMAS MULLINS Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
b A new, simple analytical radiochemical method for the purification and determination of berkelium tracer is based on a two-cycle liquid-liquid extraction system. Berkelium(1V) is extracted into 0.1 5 M di(2-ethylhexy1)orthophosphoric acid-heptane from 1 OM nitric acid followed by reduction and stripping into 11.8M lithium chloride-0.4M hydrochloric acid solution. Thirty per cent tricaprylamine-xylene is used in the second cycle to separate berkelium(lll) from cerium(lll) and to increase the decontamination from other elements. Excellent separation is effected from many elements including uranium, neptunium, plutonium, americium, curium, californium, lanthanide elements, cesium, strontium, barium, zirconium, niobium, ruthenium, nickel, iron, aluminum, silver, and molybdenum. Several useful analytical and process applications of this purification method are discussed.
A
which confronts the analytical radiochemist currently is the purification and determination of berkelium24g. I n some respects this is more difficult than that of the other heavy elements because of its unfamiliar chemistry and weak beta particle decay. Berkelium249 ( t l / z = 314 days), the major berkelium nuclide produced by high neutron flux reactors, decays >990/, by emission of low energy beta particles (E,,, = 125 k.e.v.). Therefore, separation from other radioactivities is necessary before measureCHALLEKGING PROBLEM
ment of this isotope is possible. Fortunately, it is the only transplutonium element with a stable tetravalent oxidation state in ordinary aqueous solution. The chemistry of berkelium(1V) is very similar to that of cerium(1V) (3). Previously, no simple method existed for the radiochemical determination of berkelium in mixtures of other transuranium elements and fission products. Early investigators utilized its relative elution position from ion exchange resins to isolate berkelium. Several resin cycles are required to separate berkelium from both actinides and fission products. Such procedures are time-consuming and not satisfactory for process control. Liquid-liquid extraction is a valuable method for the rapid purification and isolation of nuclides, which are relatively solid-free and suitable for beta or alpha counting. An early patent (4) in this area describes the use of tributyl phosphate in the purification of berkelium. Yields of 92y, berkelium containing 8% americium were obtained. No separation was effected from cerium, however. A definite advance was made by Peppard ( 7 ) in the application of di(2ethylhexy1)-orthophosphoric acid to separate berkelium from a number of elements. Again, no separation from cerium is effected. T o accomplish this difficult separation and enhance the decontamination of berkelium from many other elements, an adaption of the amine extraction technique ( I , 6)
has now been successfully applied. These two solvents provide a simple two-cycle liquid-liquid extraction system for the purification and determination of berkelium. EXPERIMENTAL
Apparatus. Internal sample methane proportional counter. Voltage settings of 2900 and 4300 were used for alpha counting and beta counting, respectively. N a I well-type gamma scintillation counter 13/4 X 2 inches. Reagents. Di(2-ethylhexyl)-orthophosphoric acid-heptane, 0.ltih’. Purify di(2-ethylhexyl)-orthophosphoric acid ( H D E H P ) , available from Union Carbide Chemicals Co., New York, N. Y by mixing gently with an equal volume portion of ethylene glycol. If mixed too vigorously, the phase separation is poor. Separate the phases by centrifugation. Weigh 48.33 grams and dilute to 1 liter with n-heptane. Equilibrate with an equal volume portion of freshly prepared 10M nitric acid0.1M potassium bromate for 3 minutes just before use. 10M Nitric acid-0.1M potassium bromate solution. Prepare fresh daily. %-Heptane. 11.8X lithium chloride-0.4JI hydrochloric acid solution. 30% (w./v.) Alamine 336-S-xylene. Alamine 3 3 6 4 (tricaprylaminej is a water insoluble, symmetrical, straight chain, saturated tertiary amine. The alkyl groups are a Cs-Clo mixture with the Cs carbon chain 1)redominating. I t is available in conimwcial quantities (99-100yo tertiary amine) from General Ahfills Co., Kankakee, Ill. Ililute 300 VOL. 37, NO. 6, M A Y 1965
687
