from this point until it reaches the stationary furnace, where it will be stopped by the limit switch. After standing for 5 minutes a t that point the first combustion is completed and the furnace is moved to the beginning of the track for starting the second combustion. For this operation the speed of the motor is set for approximately 1 inch travel per minute and the switch turned to direct drive. When the furnace reaches the end of its travel it is shut off and cooled for the next analysis, while the products of combustion are swept out of the tube. Twenty-five minutes are allowed to remove the water and carbon dioxide completely. The adsorption tubes are removed from the combustion train and placed on an aspirator system where they are flushed with 100 ml. of dry, carbon dioxide-free air to displace the oxygen. They are then wiped and weighed in the usual manner. ACCURACY A N D PRECISION
Table I1 shows data obtained on samples of known carbon and hydrogen content and indicates the precision and accuracy obtained by the automatic combustion procedure. The samples selected contained free carbon, carbon and hydrogen alone, and carbon and hydrogen with various other elements, including oxygen, nitrogen, sulfur, and halogens.
DISCUSSION
By using this procedure adequate contact time of the sample vapors with the copper oxide is ensured through control by the choking plug and pressure switch. The rate of flow of oxygen to the combustion tube may a t times exceed 4 t o 5 ml. per minute, because of excessive consumption of the gas by either direct oxidation of the sample or oxidation of reduced oxide formed during the combustion. However, the flow of gases from the exit end of the combustion tube will not exceed the prescribed rate established by the choking plug and pressure conditions in the combustion tube. Differences in pressure due to the resistance of the adsorption tubes are always equalized by adjustment of the hlariotte bottle instead of the pressure regulator. I n this way atmospheric pressure is always maintained a t the entrance end of the water absorption tube, ensuring equilibrium between the absorption and liberation of water by the rubber connection a t this point. The versatility of the apparatus makes it easily adaptable for various arrangements of equipment and suggests its use for other micromethods. The same principle of pressure control should be applicable to the microDumas method for determination of
nitrogrn, combustion methods for halogens and sulfur, oxygen by pyrolysis and reaction with carbon, and similar procedures. Work along this line is in progress. ACKNOWLEDGMENT
Tlic author thanks Joy Rae Hunter and Caroline Sherman who obtained many of the data shown in Table I1 and carried out numerous analyses to teEt the method. LITERATURE CITED
(1’1 Clark, R. O., Stillson, G. H., 1x11. EXG.CHEIM., ANAL.ED. 19, 423 (1947). (21 Fischer, F. O., A N ~ LCHEM.21, 827 (1049). (3, Ilallett, L. T., IND. ENG. CHEM., A ~ A LED. . 10, 101 (1938). ( 4 1 Horeischy, K , Dreher, I., Hoffmnnn,
O., Milcrochemae ver. Mikrocham. Acta 33, 221 (1948). ( 5 ) Reihlen, H., Ibid., 23, 285 (1937) (6) Royer, G. L., Norton, A. R., Sundberg, 0. E., IND.E m . CHEM., ANAL.ED. 12,688 (1940). ( 7 ) Steyermark, AI,Ibid., 17, 523 (1946).
RECEIVEDfor review June 20, 1968. -4ccepted February 6, 1959. Group session on rlnalytical Research, 23rd midyear meeting, Division of Refining, American Petroleum Institute, Los Angeles, C:xlif., May 1958.
Precise Electronic Titration Instrument Chlorinity Titration SIR: This titration instrument (a) is a vacuum tube millivolt meter of the null type for use in argentimetric titrations. Both of the instruments which we built have given trouble due to failure of 6SC7 tubes. After a tube has been in service for about 1 to 4 months it becomes unstable, as shown by random and often violent fluctuations of the null meter. This instability is associated with a marked increase in the grid current of the 6SC7. Typical grid current for a new tube in this circuit is - 3 x 10-10 ampere (6); for a used tube which has become unstable, - 2 x 10-7 ampere. This may be due to gas released by the tube elements after a period of use (metal tubes are difficult to “degas” during manufacture), to emission of electrons by the grid due to transfer of some of the cathode material to the grid wires which are very close t o the cathode in this type tube, or to a number of other causes (1, 6). This condition has been relieved by direct substitution of one of the “re1278
ANALYTICAL CHEMISTRY
liable” series of miniature tubes, Type 5751, for the 6SC7. The two sections of the 5751 are much better matched than those of the average 6SC7, so that tube selection is seldom necessary. The separate heater connections of the 5751 allow very close matching of the two sections by adjustment of the cathode temperatures. This is accomplished by a 6- to 10-ohm potentiometer connected as shown in Figure 1. This gives somewhat lower heater operating voltage, which results in longer tube life and lower grid current (4). This potentiometer has a screwdriver-slot shaft and is mounted through the chassis, near the tube socket. It is adjusted (with the front panel potentiometer at mid - range) when changing tubes and occasionally as tubes age. The grid current of the 5751 was -1.2 X 10-l0 ampere when installed and was within the same order of magnitude 4 months later. Voltage regulator tubes tend to be somewhat erratic when operated in the low current range (6). The dropping
5751 u. L
6toIOn
--w Figure 1. Base connection of miniature tube, Type 5751, with connections shown for cathode temperature a d justment potentiometer Potentiometer is set to compensate for difference in characteristics of the two triode sections
resistor, Rlo, was therefore reduced from 10 to 3 kilo-ohms. The quick heating, filament-type rectifier 51T-4 was replaced by the slon-er heating, cathode-type 5V4-G, so that the plate voltage would not be applied to the 5751 before its cathode had warmed. Cathode damage and consequent change of characteristics may
result from application of plate voltage before the cathode has reached operating temperature. Center-zero type 50-0-50 ha. meters have been substituted for the 0-50 meters with their reversing switches. The above modifications can be made on existing instruments with a minimum amount of work and result in greatly improved performance and convenience of operation. The 5751 tubes last twice as long as the 6SC7’s and do not require selection. There is still some zero-point instability in the instrument, apparently due to line voltage fluctuations. This is almost completely eliminated by plugging the meter into a Sorenson Model 150-S vacuum-tube line voltage regulator or a Sola Model 30805 constant voltage
transformer. Soine sort of line voltage regulation thus seems t o be required. Replacement of the power transformer by a Sola-Type 7104 voltage regulating power transformer (which costs only about twice as much as the regular power transformer) eliminates nearly all of the zero drift. ’ A completely redesigned instrument n-as built (3). LITERATURE CITED
(1) Elmore, TV. C., tronics,” pp. 180-3, York, 1949. (2) Harwell, K. E., 616-19 (1954). (3) Proctdr, C. hl.,
Sands, M., “ElecMcGraw-Hill, New Ax.4~. CHEM. 26,
dissertation, Texaa A&M College, January 1958. (4) Rider, J. F., “Vacuum-Tube Volt-
meters,” 2nd ed., pp. 148-51, 216, John F. Rider Publishers, Kew York,
1951. (5) Tomer, R. B., Electronics 29, No. 9, 218-30 (1956). (6) Valley, G. E., Wallman, H., “Vacuum Tube Amplifiers,” pp. 419-21, McGrawHill, New York, 1948.
CHARLES 31.PROCTOR 4676 Columbia Parkway Cincinnati 26, Ohio
CONTRIBUTION 142, Department of Oceanogra hy and Meteorology, Agricultural and Gechanical College of Texas, College Station, Tex., based in part on investigations conducted for the Texas A&M Research Foundation through the sponsorship of the Office of Kava1 Research (Project NR083 036, N70nr-487, T.O. 2’1. This communication constitutes Technical Report 56-37T (10-9-56).
Separation of Uranium and Bismuth with Ion Exchange Papers SIR: Methods for the separation of uranium from large amounts of bismuth have been investigated because of interest in Brookhaven National Laborntory’s Liquid Metal Fueled Reactor (1, 4). One method for this separation utilizes ion exchange-impregnated papers to separate uranium from 250 times as much bismuth. Tuckerman ( 5 ) has reported the use of the cationic form of these papers for the separation of basic amino acids. Little work has been done on inorganic applications. EXPERIMENTAL
A solution of bismuth and uranium mas prepared that contained 10 grams of bismuth and 40 mg. of uranium (as EOn++)in 25 ml. of a 12N nitric acid solution. Another solution contained 250 mg. of bismuth and 250 mg. of uranium. The papers n-ere washed with distilled water by allowing the water to ascend through the papers, simulating a chromatoqraphic separation. They were used as received from Rohm and Haas, IR.4-400 (Cl-) and IR-45 (OH-). After drying, a 10-pl. sample of the test solution was applied and the paper was allowed to dry. It was developed bv nicending chromatography with distilled water as the s o l ~ e n t for 45 minutes. The paper was treated with a 3% potassium ferrocyanide solution to 10cate the uranium and a saturated basic sodium sulfide solution to locate the bismuth. The uranium appears as a broil-n 5eck and the bismuth as a black streak. The IRA-400 paper contained some impurity, probably iron, which appeared with the ferrocyanide reagent. Figures 1 and 2 show the separ a t‘ions.
The weakly basic (IR-45) paper will separate small quantities of the elements, but it is not so effective as IR4400 for large amounts of bismuth. In comparison with this rapid chromatographic method, conventional separations are incomplete after 10 hours of development. Separations were tried on Whatman 3MM paper using butanol saturated with 1N hydrochloric and
nitric acids. After 11.5 hours the h y drochloric acid solvent had not caused any separation, the bismuth running from 15 to 120 mm. and the uranium a t 45 mm. After 9.5 hours in the nitric acid solvent separation was only partial, the uranium being located from 53 to 60 mm. and the bismuth from 12 to 58 mm. from the point of application.
1-
SOLVENT FRONT
-
SOLVENT FRONT
1-
IMPURITY
URANIUM FRONT I
-
BISMUTH FRONT
r”\
I-
UOz FRONT (10
Y)
POINT OF APPLICATION
Figure 1 . Separation of 4 0 y of uranium from 10 mg. of bismuth on Am berlit e IRA-4 00-im p regnoted pap e r
Figure 2. Separation of 10 y of uranium from 10 y of bismuth on Amberlite IR-45-impregnated p a p e r VOL. 31, NO. 7, JULY 1959
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