Adaptable Circuit for Constant Temperature Baths. Ernest Levens' and Richard S. Cass, Frederick S. Bacon Laboratories, Watertown 7 2 , Mass.
laboratory atmosphere; neverthelese, anticipating component failures, a simple thermal overload fuse for oil baths, or a lowwater cutoff for 11-ater baths (Figures 8 and 9), is routinely included. I n its most elaborate form the circuit shown in Figure 6 provides automatic on-off for intermittent use a t preset intervals (time-clock): rapid temperature rise a t line voltage from a cold start, with automatic return t o balanced heater input preset temperature; thermoregulator control current of less than 10 pa. a t 10 volts; corrosion-resistant contacts, not injured by relay chatter, carrying up to 3300 watts a t 110 volts; reliable hightemperature, or lowwater, safety cutoff.
'
research laboratory operations frequently require a variety of constant temperature baths, of greater or lesser complexity depending on the degree of control expected. Commercially available baths are, in general, too expensive, or need extensive modification. Some circuits recently described ( 1 -3, 6, 6) seemed unnecessarily complicated or were not readily adapted to frequently changing requirements. For several years the authors have adopted the easily modified on-off control circuit for alternating current operation (Figures 1 to 7). This circuit has proved to be rugged, durable, and yet sensitive in baths used almost continuously for 5 years. No exposed contacts are used, which is important in a corrosive HEJIICAL
1
Two water baths, using the circuits of Figures 5 and 6 (glass battery jars, one of 4.5-gallon, the other of 7-gallon capacity) enclosed in boxes of 0.5-inch plywood with 3 inches of glass wool lagging (except for cover) have operated with fluctuations of +0.005" C. or less (Beckmann differential thermometer) and
Present address American Potash B- Chemical Corp., Los Angeles, Calif. H-2
rn H-l
STIRRING MOTOR
H-2
9 6
7 18
FIG I
N-2 V.
T R. TO THERMOREGULATOR
TO V.TR
5-2
s -3
5-4
s-3
FIG. 2 s-l
Figure 1 (Middle). Basic Circuit. Figure 2 (Right). Addition of Continuously Adjustable Autotransformer and Constant-Voltage Transformer to Heater H-1. Figure 3 ( L e f t ) . Addition of Continuously Adjustable Autotransformer to Heater H - 2 C. CR-1. CR-2. C. T', H-1, H - 2 . x - 1 , 5.-2, 5 - 3 . P-1.
P-2. P-3. P-4. P-5.
P.B.
8-mfd. 250-volt condeneer Coilsfor R-1, R-2. R-3, R 4 i n parallel, 115 volts,60Coil for R-5, 115 volts, 60Constant-voltage transformer, resonant frequency type Heaters. Size depends on both volume and operating temperature S e o n bulbs 5000-ohm 5-watt resistor 51-megohm, 0.5-watt resistor 1bO-ohm, 2-watt resistor 200-ohin, 10-watt resistor 51,000-ohm. 0.5-watt resistor Push switch, spring return, normally open
R-1, R-2. R-3, R-4.
R-5. s-1. 9-2, s-3, s - 4 . T-1, T-2.
T-3. TS.
T'.
H-l
v.
T.R.
Mercury plunger relay tube normally open (H. B. Instrument Co. No. 7020) Mercury plunger relay tube normally closed (H. B. Instrument Co., NO. 7250) Mercury plunger relay tube (normally open or normallv closed a s reauired bv thermoreeulatori Double-poie single-throi t h e r m i l overload i w i t c h ' Single-pole single-throw switches Variable autotransformers (General Radio Co. Variac) 6.3-volt 1-ampere filament transformer Time switch 2D21 vacuum tube Vacuum tube relay (see detail diagram, Figure 7)
?-2
Wwr
CR-I PB
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Figure 4. Rapid Rise (Automatic) with Fixed Voltage Operation
Figure 5. Rapid Rise (Automatic) w-ith Variable Voltage Control on Heater H-1 1685
Figure 6. Rapid Rise (Automatic) with Variable Voltage Control and Time Sw-itch
1686
ANALYTICAL CHEMISTRY
TO H-2 OR VARIABLE AUTO-TRANSFORMER
‘
t
or lower temperatures-for example, various combinations of bismuth, lead, tin, cadmium, copper, and antimony melt from 65.5” C. (Wood’s metal) to 327” C. (chemical lead), a practical range for baths using water or organic fluids.
Microswitch SPOT # B Z - Z R L
Stopper wired on
9CKNOB LEDGMENT
+
I
VOLTAGE
A portion of this nork was sponsored by the Instrumentation Laboratory a t the Massachusetts Institute ot Technology, and permission to p u b Iiih this p a p e ~i i giatefullj achnov 1etlgrd.
i
SOURCE
Figure 7 . Vacuum Tube Relay Wiring Circuit
Figure 8.
Low-Water Cutoff
LI’TI3KYrURE CITED
(1) Baldeschwieler and Wilcox, ISD. ESG.
CHEM.,A x n . ED., 11, 221 (1939). with no drifting. Operation near room temperature may require a cooling coil to balance pump or stirrer heat input; this can be done either a t constant coolant flow rate through a pressure regulator, or with a solenoid-operated injection system. The authors have used constant flow cooling (Fisher Scientific Co. S o . 15529 water pressure regulator) in a pump-stirred bath below 50” C. with excellent results; a propeller is less troublesome than the pump, aq it delivers less hPat to the system. Efficient agitation ip extremely important.
3-hole stormer
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roclor 1260 ( M o n s o n t o igh dielectric non-volatile)
12 B 8 S ga. bare copper wire 3 m m i.d. pyrex tubing
50/50 cored solder- 1/8 in. dia wire r n p 225Oc
Figure 9.
High Temperature Cutoff
The vacuum-tube relay (Figure 7) is a conventional trigger circuit actuating a high current-carrying relay. lThe mercury plunger relay tube, R-5, may be either normally open or noi,mally closed (H. B. Instrument Co.; No. 7020 normally open, S o . 7250 normally closed) as needed for the thermoregulator used; (AmericanInstrument Go., Metastatic, or H. B. Instrument Co. s Red-top mercury thermoregulators require R-5 to be normally open; bimetallic thermoregulators like Cenco de Khotinsky or Fenwal require R-5 to be normally closed.) Because of a possible slight shock hazard if the thermoregulator leads were shorted t o ground, Figure 7 may be modified by replacing the 51,000-ohm resistor, P-5, with a 25,000-ohm resistor and adding a 25,000-ohm resistor in the thermoregulator lead coming from resistor P-2. Each lead would then have a high resistance, reducing any shock hazard. Heater input is split so the major load is carried by one continuously operating heater, H-1, set to deliver just insufficient power to maintain the temperature setting (about 80% of total power input). The second heater, H-2, controlled by the thermoregulator, supplies the deficiency a t such a rate that it is on about 50% of the time. Over- and undershoot are t’hereby minimized. Heater combinations of 500 nratts H-1, plus 300 watts, H-2, for operation up to 100” C. in a 7-gallon bath, and 1000 watts plus 300 watts for use up to 200” C. in a 10-gallon bath have proved satisfactory; adjustment with autotransiormers (Variac, Powerstat) permits operation between room temperature and the maximum. The weighted float (Figure 8) used as a low-w-ater cutoff, operates when the level drops about 1 inch; many modifications are possible. The fusible link (Figure 9), used as a high tempet’ature fuse in oil baths, was designed by Cass when no commercial item of this type could be found. The 50-50 lead-tin solder link melts at 225’ C.; other alloys can be obtained or mad? (4)for higher
(2) Hawes. I h i d . , 11, 222 (1939). (3) Hersh, Fry, and Fenske. Ind. E n y . Chem., 30, 363 (1938). (4) Hodgmaii, C. D., “Handbook of Cheniisfry and Physics,” Chemical Ruhher Publishing Co., 35th ed., Cleveland, 1951. (5) Muller, 1x0. Esc. CHEU.,-4x.k~.ED.,12, 571 (1940). (6) Sturtevant, “Temperature Control,” in Weissberger, “Technique of Organic Chemistry Physical Methods,” 5’01. 1, P a r t I, 2nd
ed., Xew York, Interscience Publishers, 1949.
Apparatus for Distillation and Stirring. Sornian S.Radin, Biochemical Institute, Universit.y of Texas and the Clayton Foundation for Research, Austin, Tex. RIsT-action type of swirling can readily be imparted to liquids by the inexpensive apparatus pictured in the right side of the diagram. This type of motion permits use of the apparatus for vacuum distillations without a capillary leak and for Iiiixiug without the use of a propeller or magnetic bar. The swirling motion is produced in flask A (which can also be an Erlenmeyer) by the “handle,” B, which is moved by a size 12 rubber stopper, C. The stopper contains a ‘/g inch diameter hole, wetted with glycerol, and rotates by means of a pair of closely fitting cork borers. The inner borer is inserted into the center of the stopper and serves as shaft; the outer borer is sawed short and serves as bearing. The stopper is driven by a variable speed mot,or, using a ‘/r-inch steel rod tipped by a short piece of rubber tubing, D. The weight, of t,he flask is supported flexibly by two lengths of rubber tubing, E, which are twisted about six times and held at the ends by t’wo buret clamps. Additional clamps are necessary a t points F . B is made by sealing 3 inches of heavywalled capillary tubing to the stoppering tube and then sealing the opening. With the same apparatus flask sizes of 50 t o 1000 1111. have been used, as n-ell as test tubes. The remainder of the diagram illustrates application to solrc~nt removal under vacuum.
F
I
IF
The condenser, G, is a %-liter flask with a side arm sealed 011, and is cooled by a stream of water and suspended at the neck by a short loop of rubber tubing. Condenser and distilling flask are connected by a 10-inch length of 1/2-inch (inside diameter) pressure tubing, H. The relative inflexibility of this tubing makes necessary the free suspension of the condenser. By raising the condenser above the level of the distilling flask, unwanted solvcsnt is automatically disposed of into the aspirator water.
