2032
ANALYTICAL CHEMISTRY
’”ol 80
Power Supply for Zone Electrophoresis, Electrodialysis, and General Use Charles M. Proctor, Department of Oceanography, Agricultural and Mechanical College of Texas, College Station, Tex.
evaporation mill cause the resistance of I the stripelectrophoresis, to go down, because of an increase in concentration N ZONE
Figure 3.
b / d /C
/d
Calibration chart
e/
//
Figure 4. Protective mount for probe-type thermistors Thermistor Victory32.41 32.111,51.41, or Stantel F type Via-inch tubing flare nut,’long type. Water circulation slots cut with hack saw C. l/r-inch rubber grommet. Fits Victory, ream out f o r Stantel d. g/la-inch tubing X l/a-inch female IPS compression connector. N u t not used. Ream out f o r Stantel C. l/a-inch brass nipple. At least 4 inches long f o r Victory 32.411, 6 inches or longer f o r others. d and g sweat-soldered i o nipple f. Flexible grounding wire from shield t o hole in nipple U. ‘/,-inch tubing X l/s-incli female I P S compression connector with nut. Ream out t o fit cable rubber grommet. Trim edges t o fit inside nut h. ”a-inch Microphone cable, Beliien type 8422, two-conductor, shielded, \.inyl insulation a. b.
reset to within 0.02’ C. (test a t 42’ C). A year after the original calibration the instrument setting was rechecked a t several temperatures from 0’ to 80’ C. No change in calibration was observed. Line voltage changes from 100 to 130 volts have little effect on performance of the controller. LITER.ATURE CITED
(1) Geppert, V., “Basic Electron Tubes,’’ pp. 2i6-99, McGraw-Hill, New York, 1951. (2) International Rectifier Corp., El Segundo, Calif., Bull. H-2, (1954), “Hi-Voltage Selenium Rectifier Cartridges.” (3) Proctor, C. M., Dept. of Oceanography, A. and 31. College of Texas, College Station, Techn. Rept. Ref. 55-15T, ( L I s r c h 28, 1956). ( 4 ) Proctor, C. AI., Rev. Sci. Inslr. 22, 1023-4 (1951). (5) Richter, Walter, “Fundamentals of Industrial Electronic Circuits,” pp. 418-28,436-50, McGraw-Hill, New York, 194i. ( 6 ) Seely, Samuel, “Electron-Tube Circuits,” pp. 32-7, 281-9, McGraw-Hill, New York, 1950. (7) Walker, R. C., “Industrial Applications of Gas-filled Triodes (Thyratrons),” pp. 44-54, Chapman & Hall, London, 1950. CONTRIBUTIOK from t h e Department of Oceanography, Agricultural and Mechanical College of Texas, Oceanography a n d Meteorology Series No. Based in part on investigations conducted for t h e Texas A & M Research Foundation through the sponsorship of t h e Office of Naval Research (Project K R 083 036, N7onr-487 T.O. 2) and during the author’a tenure a s Dow Research Fellow in chemical Oceanography. 85.
of the supporting electrolyte. Constant current is therefore recommended for most applications, in order to limit heat dissipationin the strip [Raymond, Samuel, Science 120,677-8( 195413. The conditions are different in electrodialysis, where the cell resistance rises to a very high value as salts are removed from the solution. As dialysis progresses, the voltage across the cell should be increased to speed removal of the last traces of salt. Inverse current regulation is needed, hoFvever, to avoid overheating the cell. The power supply shown in Figure 1 was built for exploratory scale electrophoresis and electrodialysis studies.
A 6AG7 is used as regulator tube with switching for pentode operation to give constant current, triode operation for inverse current regulation, and the regulator tube made inoperative when the unit is used as a straight power supply with either choke or condenser input filter. The same basic circuit could be used for higher voltages and currents by selecting a larger tube and appropriate components. Circuit Design Considerations. The eight terminals a t the right of Figure 1 are connections to an octal socket on the front panel. Separate cords are used for regulated or unregulated output, and for condenser or choke input. The labels on the drawing indicate the pin jumpers that should be placed in the cord plug for various operating conditions. The no-load output from the filter is about 300 volts with choke input, 370 volts with condenser input. The 1-megohm resistor allows the first section of the filter condenser to charge, the time constant (RC) is 10 seconds, with no output plug in the socket. This prevents a current surge if an output cord is connected to the supply while the rectifier is operating. The regulator tube heats only when there is a plug jumper between terminals 2 and 3. Pentode Operation at Constant Current. The screen grid current of a pentode varies as an inverse function of the plate current. Cathode degeneration cannot be used for plate current regulation, if the screen return current flows through the cathode biasing resistor. A separate scrwn voltage supply is therefore neressnry for good regulation.
It is obtained from a small 115-volt, 15-ma. transformer with a 6.3 volt, 0.3-ampere heater winding. A 12AU7, with grids and plates connected together, is a satisfactory rectifier. ( A transformer such as Stancer PS-8415 and a 6 X 4 rectifier could be substituted.) The No. 48 lamp (2 volts, 0.06 ampere) serves as a screen current indicator and fuse. Under normal operation, the lamp will never show more than a barely perceptible glow. With the operation control switch in position 1, the screen supply transformer is connected to the power line, the regulator tube is pentode-connected, and the control grid potentiometer is connected to the bleeder resistor t o provide a positive reference potential for operation with cathode degeneration. A functional outline of the pentode-connected circuit is given in the lower right corner of Figure 1 for greater clarity. The 6.1G7 is rated for 9-watt plate dissipation. With a very small value of load resistance, the prate to cathode potential may reach 300 volts. The regulator is therefore designed for maximum operating current of 30 ma. This operating current is covered in two ranges: 0 to 10 ma. and 0 to 30 ma. With the range switch in “low” position, the cathode resistor is 8500 ohms and the meter operates with normal scale. When the range switch is moved to “high,” the value of the cathode resistor is reduced to 2500 ohms and a 3x shunt is connected across the meter. For the various models of panel mount, 10-ma. meters are currently being listed in the radio supply catalogs; those made by Triplett have a nominal resistance of 3.1 ohms; by Simpson, 10 ohms. The shunt should be one half of the meter resistance. The load current us. voltage curves are shown in Figure 2.
2033
V O L U M E 28, NO. 12, D E C E M B E R 1 9 5 6 JUvlPER FILTER COND 4 8 - 7 FOR COND INPUT
9Hy -
CHOKE ,INPbT SlDE
-08-
6 FOR CHOKE INPUT
8- REGULATED
I
UMPER 2 - 3 USING
B
/
b+
-
WHEN
REGULATOR
UNREGULATED
OUTLINEE O F CIRCUIT. CONNECTED
d PENTOOE
E,
Figure 1.
Circuit of regulated power supply
This power supply gives constant or inverse current regulation at the turn of A switch. I t may also be used unrrgulatrd f o r plate and heater supply. A safety interlock switch may be connected a t point S. T h e potentiometer is Ohmite-type CB 5031, with switch.
The powcr supply regulation curve, measured a t the output of the filter, is given a t the right of the figure. With the 4-pf. condenser across the load, the ripple a t 300-volt output is less than 0 . 0 1 as ~ ~estimated with the aid of an oscilloscope. Voltage regulation of the screen supply is rather poor. The performance could be improved by using a voltage regulator tube in the screen supply, but the degree of regulation shown in Figure 2 is adequate for present use. If the load circuit were opened while the power supply is on, cathode bias would be removed. Screen current would then soar, burning out the No. 48 lamp. The 0.47-megohm resistor would limit the control grid current to a safe value. The only damage to the circuit would thus be one burned-out bulb. Triode Operation, Inverse Current Regulation. For triode operation the control switch is set in position 2, the screen supply is turned off, the tube is triode-connected, and the grid potentiometer is connected for variable cathode bias. The allowable plate voltage for triode connection is higher with the suppressor grid tied to the plate than if it were a t cathode potential. Power dissipation by the screen should also be lower. The 1.5-kiloohm resistor in series with the grid potentiometer provides a minimum grid bias when the potentiometer is in full range position. The 0-10- and 0- 30-ma. range switch functionsas before.
41
0’
0
I
50
100
-Li--L-150 200
250
300
1
I
350
400
LOAD VOLTAGE
Figure 2.
Pentocle operation a t constant current
The triode operating curves are given in Figure 3. For each setting of the grid potentiometer, the load resistance was increased iri six to ten steps, starting from zero. Current through the load varies inversely with the voltage drop across it. The dotted curves show the calculated load power dissipation for each of the current-voltage curves. In actual operation with an electrodialysis cell, load resistance and load voltage will start not a t zero but a t some point along an operating curve. -4s dialysis proceeds, the current-voltage relations can be predicted from these curves. Unregulated Operation. With the operation control switch in position 3 and no connection between pins 2 and 3 of the cable plug, the unit acts as a choke or condenser input power supply, depending on the connection of pin 8. The output voltage-current curve for condenser input operation is the same as the supply voltage curve shown a t the right of Figures 2 and 3. Maximum output current from the specified transformer is 40 ma. of which the bleeder takes 10.
For each curve, the current-control (grid bias) potentiometer was set with zero load resistance. T h e load resistance was then increased until the current dropped sharply. T h e maximum usable \ d u e of load resistance is given beside the break in each current ciisve. The supply voltage changes with load current, vertical curve a t the right of the figure, and was measured between terminals 4 and 6.
With choke input connection: the no-load voltage drops t o 300, regulation improves considerably, maximum available output current is 45 ma. (Langford-Smith, F., “Radiotron Designer’s Handbook,” 3rd ed., chap. 22, 23, RCA, Harrison, N. J., 1945) and filtering efficiency much lower. NOTES AND COMLMENTS
For convenience in handling, the unit was built into a 6 X 9 X 5 inch steel cabinet. The cabinet should be large enough to provide a compartment for storage of output cables with the various plug connections.
ANALYTICAL CHEMISTRY
2034
and a monthly sulfate determination. In this laboratorj- a method has been developed involving the titration to a pH of 3.5 for nitric acid content, a continued titration to a p H of 7.0 for the aluminum salt content, and an ion exchange method for the determination of sodium sulfate. This method eliminates the long and tedious gravimetric procedures previously used, without sacrifice of accuracy. Ion exchange has been used for total cation determination in inorganic analysis (Samuelson, O., "Ion Exchangers in Analytical Chemistry,'' Wiley, Yew York, 1935), and recently a method n-as brought to the authors' attention in which the ion exchange principle was applied to the analysis of iron pickle liquor [Fisher, S., Kunin, R., ANAL.CHEM.27, 1649 (195511.
-113200
- 2 3
-0
53
Figure 3.
100
150 200 250 LOA0 VOLTAGE
300
350
400
Triode operation, inverse current regulated
As the load resistance is increased froni zero, the load voltage rises and current drops. The power dissipation in t h e load is shown by dashed lines. Supply voltage curve is as for Figure 2.
An unexpected use for the current-regulated supply wis found in deterniinirig the closing and opening currents of a group of plate circuit, relays. For safety in the chemical laboratory, no part of the circuit should be connected t o the chassis. The chassis should be grounded; 300 volt,s a t 30 ma. can be very uncomfortable and can be dangerous !Then the hands are wet. For this reason a safety-interlock sivitch is provided on most commercial electrophoresis cells, so that power is removed when the cell cover is opened. This safety switch should be connected between the fuse and the power switch. The filter can be permanently connected for condenser input, leaving socket terminals i and 8 for the safety switch leads. For less critical current control t8heseparate screen supply may be omitted and screen volt'age obtained from the high voltage supply through a 25-kilo-ohm, lO-m,att dropping resistor. The cont,rol grid is conneckd to B - and cathode bias iised. The cathode rcaistor may consist of two 4-watt wire-nyound potentiometers iii series, a 5000 ohm and a 500 ohm for coarse and fine control, respectively. The current drop n-it,h increasing load is about 5 times as great with this modification. When half-wave rectification is used for the plate supply the ripple is only about 0.02%. The above circuit may thus be adapted for operation up to about 1200 volts by using a t,ype 5R4GY as half-wave rectifier with a good quality receiver-type transformer for the plate supply and using an 807 (or higher voltage) transmitting type pentode for the regulator tube. Adequate precautions against shock are mandatory. CONTRIBCTION from Department of Oceanography, Agricultural and hlechanical College of Texas, Oceanography and Meteorology Series No. 66 Based in part on investigations conducted for the Texas A & M Research Foundation through sponsorship of the O E c e of Naval Research (Project N R 083 036, Sionr-487, T. 0 . 2 ) .
Analysis of Pickling Bath Solution Using Ion Exchange Florence Nesh and Edward C. Haas, Naval Material Laboratory, New York Naval Shipyard, New York, N. Y.
reagent control of pickling bath solutions used to clean the surfaces of aluminum and aluminum alloys preparatory t o spot welding is effected by a weekly titration for acid content THE
The cleaner is composed of 15% by volume of 42" Baumk nitric acid, 13 ounces per gallon of sodium sulfate decahydrate (Glauber's salt), and the balance water. The solution, when in use, is maintained a t a temperature of 180" t o 190" F. The ion exchange column used consisted of 40 grams of the cation resin Amberlite IR-100, the hydrogen form, packed in a 100-ml. buret with a plug of glass wool a t the bottom. The total exchange capacity of this resin i j 1.7 meq. per gram and 0.6 meq. per ml. It was determined by experiment that 24 meq. of sodium ion would saturate 25 grams of resin. The following procedure is recommended for the analysis of prespot weld aluminum pickling bath solution. Take 5 ml. of the pickling bath solution and dilute to 250 mi. in a volumetric flask. Take a 25-m1. aliquot of the diluted solution and titrate to a p H of 3.5 (or t o a methyl orange end point); continue titrating to a pH of 7.0 (or to a phenolphthalein end point). Take another 25-ml. aliquot of the diluted solution and pass it through the ion exchange column. The figure a t pH 3.5 gives the nitric acid content and the figure at p R 3.5 to 7.0 gives the aluminum salt content. The total of these two figures subtracted from the eluate figure gives the sodium sulfate content. To verify the procedure, a solution was prepared from accurately weighed amounts of pure anhydrous sodium sulfate. nitric acid (specific gravity 1.42) and pure aluminum wire and the whole was diluted to simulate a partially depleted pickling bath. This synthetic solution was analyzed, with the follon.ing results. hfeq. in Aliquot 1.37 2.20 0.110
Meq. Found 1.32 2.15 0 104
THEopinions or assertions contained in this paper are the private ones of the authors and are not t o be construed as official or reflecting the m e w s of the Naval Service a t large.
Buret Pump for Handling Two-Phase liquids in Quantitative Analysis W. R. Dunnavant, Chemistry Research Branch, Aeronautical Research laboratory, Directorate of Research, Wright Air Development Center, Wright-Patterson Air Force Base, Ohio
is sometimes necessary to standardize I-usolutions whichworkareit unstable in contact with air. These ACALYTICAL '
solutions are commonly stored under a protective layer of a lew dense immiscible liquid and are handled during titration by means of an apparatus requiring an inert gaseous atmosphere, or an evacuated system in order to prevent decomposition. These types of systems generally use a buret connected to the supply of solution to be titrated and frequently result in titrations of solution contained only in the connecting tube and not truly representative of the bulk of the solution, regardless of how well it has been mixed. The pump described is a rapid, convenient, and accurate means of titrating unstable solutions or liquids which have been
