415
V O L U M E 2 6 , NO. 2, F E B R U A R Y 1 9 5 4 Tahle 111. Refractive Indices of Morpholine-Benzene Solutions Experimental Data Refractive index, Benzene, n D a t 25 00’ C. weight % ’
-
0
1 ,4528
10.9 23.0 31.2 40.3 50.6 63.7 71.7 85.2 92.2 100.0
1.4587 1,4647 1.4685 1,4727 1,4770 1.4828 1.4862 1.4920 1.4949 1.4979
~~~
Smoothed Values Refractive index, Benzene, weight % n g a t 25 00’ C. 0
1 ,4528
10 20 30 40 50 60 70 80 90 100
1.4582 1.4631 1.4679 1.4725 1.4768 1.4812 1.4855 1.4898 1,4940 1.4979
~~~
Table IV.
Refractive Indices of Morpholine-Ethyl Alcohol Solutions
Experimental Data Ethyl alcohol, Refractive index, weight % ’ n~ a t 25.00° C. 0 10.9 21.2 29.2 44.7 .53.4
60.2 70.8 80.1 89.1 100.0
Table V.
1.4528 1.4430 1.4337 1.4267 1.4121 1.4040 1 ,3973 1.3872 1.3786 1 ,3700 1.3593
4.5
9.0 12.9 17.1 20.9
25.2 29.7 34.7 38.3 49.5 60.1 71.1 80.2 92.5 100.0
0 10 20 30 40 50 60 70 80 90 100
1.4528 1.4441 1.4352 1,4260 1.4168 1.4071 1.3977 1.3880 1.3784 1.3688 1.3593
Refractive Indices of Morpholine-Water Solutions
Experimental Data Water, Refractive index, weight % nD a t 25.00° C.
n
Smoothed Yalues Ethyl alcohol, Refractive index, weight % ’ n D a t 25.00° C.
Smoothed Values Water, Refractive index, weight % R D a t 25.00° C.
1,4528 1.4514
0
1 ,4490
10 15
1.4471 1.4448 1.4407 1.4368 1.4313 1.4253 1 ,4208 1.4044 1.3899 1.3734 1.3600 1.3428 1.3321
5
20 30 40 50 60 70 80 90 100
1.4828 1.4508 1.4486 1.4456 1.4417 1.4310 1.4180 1.4040 1.3896 1.3754 1.3606 1,3464 1.3327
and i M . 0 mm., and 80.20” C. and 762.4 mm., respectively. \Vatcr used in the morpholine-water system was purified in a conductivity still and boiled under vacuum in order to ensure iwnoval of carbon dioxide. I(:thyl alcohol (Roesville Gold Shield alcohol, Coniinercial Solvcbnts Corp.) waa used without further purification.
Table I lists the refractive indices of the compounds used and the literature values are shown for comparison. PREPARATION O F SOLUTIONS AND REFRACTIVE INDEX DETERMINATIONS
Solutions of varying morpholine concentration were prepared by pipetting morpholine into 25-ml. glass-stoppered weighing bottles containing a weighed amount of the other component of the binary system. The actual amounts of each constituent added were determined by weighing to 0.1 mg. on an analytical balance. A Zeiss Abbe refractometer was used to measure refractive indices. According to the manufacturer, the refractometer readings are furnished with a degree of accuracy of about 2 units of the fourth decimal. A constant temperature bath and circulating pump maintained temperature a t 26.00”, with a variation of &O.0lo C. which was observed on a calibrated Beckman thermometer. A temperature control of no better than 1 0 . 2 ’ C. is required for an Abbe-type refractometer. The temperature of the refractometer prisms was measured by a calibrated thermometer, inserted in the prism jacket. Large scale plots of t’he refractive index data were prepared and values were obtained a t even composition increments, from smooth curves through the points. The maximum experimental deviation from the smoothed rurves was 4 X lo-‘ unit, corresponding to a composition difference of about 0.2% by weight. The general experimental deviation was 2 X unit, allowing for an accuracy of =kO.lOj, by weight in determining concentrations. I t is possible to use these reported data for the determination of concentrations of the binary morpholine solutions studied over the entire concentration range with one exception. I n the morpholine-mater system the refractive index of the mixture changes very slowly in the 0 to 20% by weight water region. This small change does not allow for accurate composition determinations by the refractive index method in this region. Experimental data and smoothed values are presented in Tables I1 to T:. LITERATURE CITED
(1) Dermer, V. II., and Dermer, 0. C., J . Am. Chem. Soc., 59, 1148
(1937). (2) Greenberg, R. B., U. S. Patent 2,313,537 (1943). (3) Smith, T. E., and Bonner, R. F., ANAL.CHEM.,24, 517 (1952). (4) Tilton, L. W., and Taylor, J. K., ,J. Research Natl. Bur. Standards, 20, 419 (1938). (5) Washburn, E. W.,Ed., “International Critical Tables,”’ Vol. VIL, New York, McGraw-Hill Book Co., 1929. (6) Wilson, A. L., Ind. Eng. Chem., 27, 867 (1935). (7) Wojciechowski, M., J . Rcsearch S a t l . RUT.Standards, 19, 347
(1937). RECEIVED for review July 17, 1953.
Accepted October 19. 1953.
Electronic Coulometer K E N N E T H W. K R A M E R ’ and ROBERT B. FISCHER Indiana University, Bloomington, lnd.
S
ISCE the enunciation of Faraday’s laws of electrolysis in
1832-33, several different types of coulometers have been devised. Among the more prominent ones have been weight coulometers using silver or copper, volume coulometers using mercury or which decompose water to hydrogen and oxygen, and titration coulometers of iodine, vanadium, and sodium. Although several of these have proved useful, even in extremely accurate work, recent developments in analytical chemistry have suggested the need for some more practical coulometers. One new electronic millicoulometer has been reported in the literature (f), in which current integration is achieved with a direct current motor whose armature oscillates, rather than rotates completely. The rate of angular motion of the armature is pro-
’ Present address, U. 6. 55,386,677, Detachment 2 , Army Chemical Center, hl d
portional to the current flowing through it; so the frequency of oscillation is proportional t o the current. The oscillations of the armature are registered on a commercial scaling unit. An electromechanical integrator has also been reported (2), in which a mechanical ball and disk integrator is controlled by a pen drive mechanism from a n ordinary recording potentiometer. The circuit diagram for another new type of electronic coulometer is shown in Figure 1. The circuit is basically a classical thyratron relaxation oscillator with a special frequency control such that the total number of discharges through the thyratron over a period of time is proportional to the total quantity (coulombs) of current flowing through a resistor during that period of time. The current to be summed up is passed through resistor RB,thus influencing the grid-cathode potential of the control tube, the 657. This grid-cathode potential determines the effective cathode-plate
ANALYTICAL CHEMISTRY
416 +824.1-
i
1
i P l
Figure 1.
1.1.).
+
- B3
I
Circuit Diagram
Bi. Battery, 22.5-volt Rz. Battery 7.5 volt B3. B batteiies i n series, 5-45-volt
Ci. Tubular capacitor, 0.5-mfd. C2. Tubular capacitor, 0.01-mfd.
Ri. Rz. Ra.
RI. Ra.
X.
Y. Not
Resistor, 1-megohm, 5-watt Resistor, O.Z-megohm, 0.5-watt See text Resistor, 50,000-ohm, 0.25-watt Potentiometer, 10,000-ohm T o current to be summed up, connected so that t h e electron flow i s to To scaler and counting device (such as Nuclear Instrument and Chemical Corp., Model 163) shown: 6.3-volt transformer t o supply heaters of both tubes
-
+
resistance of this tube; this relationship is linear if the tube possesses a linear transfer characteristic. Capacitor C1 charges from battery B3 through the control tube, so the plate-cathode resistance of the control tube determines the rate of charge of C,. The frequency of the discharges of C1 through the thyratron tube is determined by this charging rate, along with the capacitance of C1 and the grid voltage of the thyratron, both of which are maintained constant. Thus the number of discharges of C1 through the thyratron tube over any stated period of time is a measure of the quantity of current passing through R, during that period of time. The thyratron discharges are counted with a commercial scaling unit and mechanical register. The 657 tube was chosen as the control tube because of its sharp cutoff characteristics. An 885 tube could be substituted for the 884 with corresponding substitution of a heater supply of the proper voltage. The plate supply voltage, Ba, must be well regulated; othera-ise this factor will also influence the charging rate of Cl. Although batteries were used as B3 in the present apparatus, a conventional electronically regulated power supply should be adequate. The resistance of R3 must be such that the voltage drop across R3 with maximum current flow through it nil1 not exceed about 10 volts. Thus a value of 1000 ohms is suitable for current flows up to 10 m a , while 5 ohms is suitable for current flons up t o 2 amperes. The instrument was characterized first by determining the number of counts per minute with various known voltages applied between the control grid and cathode of the 6J7 tube. Data are shown in Figure 2, which represents essentially a transfer characteristic for the 657 tube. In this coulometer, linearity is essential, and a steep slope is desirable from the standpoint of sensitivity. The data plotted in Figure 2 were obtained with a load resistance, R1, of 1 megohm and are seen to fulfill these two requirements nicely. Greater sensitivity is achieved with a lower value of R1, but only a t the cost of decreased linearity in the cutoff region. The cutoff grid voltage is seen on Figure 2 to be about - 10.8 volts. Thus the useful range of operation would include voltage drops of zero to about 10 across Ra. I n practice, the grid potential should be adjusted with Rj to cutoff-Le., point a t which counting is just prevented-xith no current passing through R3. Then the current to be summed up is passed through ROin the direction such that the potential developed across R3 opposes that across Rg. The instrument was characterized next by passing known current flows through R8 for knolvn periods of time and determining the number of counts per coulomb for each. It was found that measurements were reproducible within 1 or 2 counts in a total of 2000 counts if no adjustments were made between replicate runs. As only a simple d'Arsonva1 current meter was used for the current measurements, it was not possible to make current readings accurately enough to make further instrument checke by this method.
Thirdly, and perhaps of most significance, the instrument was characterized by an experiment involving the electrodeposition of copper. I n effect, the instrument was thus checked against a copper weight coulometer. A manually controlled constant cathode potential deposition circuit ( 3 ) was employed for the electrolysis circuit, with resistor Rs in series with the electrolysis cell. Prior to each deposition, the 6J7 tube was adjusted to cutoff by means of Re with the deposition circuit completely assembled and connected, except that there was no copper in the solution in the electrolysis cell; thus any residual current flow through the electrolysis cell would not be counted. Then copper was added as copper sulfate and the deposition allowed t o proceed.
1. CALIBRATIONRUN. Copper was plated a t about 0.5 ampere for a short period of time from a solution containing a large excess of copper; 2229 counts were registered, and the weighed amount of copper deposited was 0.0874 gram. From the equation, counts registered Counts per coulomb = X 0.0003294 grams of copper deposited the number of counts Der coulomb was found to be 8.40. The factor 0.0003294 represents the number of grams of copper deposited per coulomb as calculated from the equivalent weight. 2. Copper was plated by the limited cathode potential method with the current flow ranging from 1 ampere a t start to 0.05 ampere when stopped; 12,210 counts were registered and the copper deposited weighed 0.4791 gram. From the total counts and the counts per coulomb factor determined in the calibration run, using the equation Grams of copper = counts registered X 0.0003204 counts per coulomb the calculated weight of copper was 0.4788. Thus the electronic coulometer data checks the copper gravimetric data well within 0.1%. 3. Copper was plated as in step 2 with the current flow ranging from 0.5 to 0.05 ampere; 2841 counts were registered and the copper deposited weighed 0.1121 gram; the weight of copper calculated from the total counts is 0.1114 gram. Thus the electronic coulometer data check the copper gravimetric data to about 0.6% even with this small amount of material and correspondingly fewer total counts. Greater accuracy in step 2 could be obtained with a larger value of RBand a corresponding calibration run. 1000,
Figure 2.
Ep
OK
6J7
Linearity Check of Instrument
This instrument thus does yield data that are measures of the quantity of electricity flowing through a fixed resistor. Measurements are accurate well within 1% over rather wide ranges of conditions, and can be much better over more limited ranges. LITERATURE CITED
(1) Bogan, S., Meites, L., Peters, E., and Sturtevant, J. &I., J . A m . Chem. Soc., 73, 1584 (1951). (2) Lingane, J. J., and Jones, S. I., h . 4 ~ CHEM., . 22, 1220 (1950). (3) Willard, H. H., Merritt, L. L., and Dean, J. A., "Instrumental Methods of Analysis," p. 246, Sew York, D. Van Nostrand Co., 1951. RECEIVED for review June 25, 1953. Bocepted September 1 1 , 1953. Publication 602 from Chemistry Department, Indiana University.
