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 i t 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.
V O L U M E 2 4 , NO. 10, O C T O B E R 1 9 5 2
1687
For smaller samples. or where a lower distillation temperature is wanted, it is desirable to use a mechanical vacuum pump, a trap, and a stationary condenser (cooled by dry ice) which is attached t o the moving flask A, by a 10-inch length of l/l-inch (inside diameter) rubber tubing. The condenser design of Flosdorf is used ( 2 ) . The vacuum should be applied slowly to minimize splashing during the deaeration. This apparatuq, when used for solvent removal, i.i similar t o that of Craig et al. ( 1 ) in that capillaries are avoided and quantitative recovery of solute is simplified. The latter design has the advantage of being all-glass and requiring less adjustment with ench use. However, the apparatus described here is more verq:ttile, is easier and cheaper t o build, can be disassembled for storage more readily, and the distilling flask can be filled more completely. When used for stirring, the “ s w i r l d ’ has the advantage over magnetic and propeller stirrers in t h a t quantitative recovery of solution can be iiiade without adding rinse solvent. As JTith magnetic stirrers, gas-tight stirring is easily performed. LITERATURE CITED
Scale for Rapid Determination of Chromatographic R/ Values. Ralph 51. Settleton, Jr., and ROVB. Ilefferd, Jr., Southwest Foundation for Researrh and Education and Trinity Cniversit!, San Antonio, Tex. widespread use of paper chromatography in chemical and biological laboratories has resulted in an ever-increasing degree of standardization in methods. This in turn has permitt d the application of these method5 to many problems hitherto
T
W Figure 2.
Spiral Rj Scale
Formnla: r = Ic(a
( I ) C‘iaig, L. C.. Giegory, J. D., and Hausmann, W,, - 4 ~ 4 CHEv., ~ . 22, 1462 (1950);, ( 2 ) Flosdorf, E. W., Freeze-Drying,” p. 17G, Yew York, Reinhold Publishing Corp., 1949.
ITC
into tcn proportional parts and lines parallel to the h>-potenuse arc constructed from each point. -4special scale designed in this manner, but combining three triangles on one scale and, therefore, capablc of being used over a wider range of wlvrnt advances, is shown in Figure 1.
.
Figure 1.
+ Ir
fi sin
(9
A very useful scale may be constructed by plotting any of several possible spirals or involutes upon polar coordinate graph paper. An equation that has been found in this lahoratory t o be useful for the construction of such a scale is:
where r is the distance from the origin to the spiral a t an angle e, k represents the R f value and varies in steps of 0.1 from 0 to 1.0,a is the minimum height of solvent advance to be employed in any determination, b is the difference between a and the maximum height the solvent will be allowed to advance in any determination, and 1.414( 425 is a correction factor. -4specific example
Special Triangular R f Scale
Plotting details. Base line extends 20 and 2.5 inches t o left and right of origin, respectively; perpendicular line extends 5 inches above origin: 10-inch line parallel t o , and 5 inches above base line, t o left and intercepting perpendicular line. Terminal points of these lines are connected. and 10 equidistant parallel lines are drawn a s shown.
considered impracticable because of the large numbers of sample- and determinations involved. The determination of R/ vdues (ratio of the distance the given unknown has advanced upon the paper t o the distance the solvent has advanced) becomes laborious and time-consuming where large numbers of c.hromatogranis are made. Two measuring devices have been prcviously described [Phillips, D. M. P., .Vatwe, 162, 29 (1948); Rockland, L. B., and Dunn, AT. S., Sczence, 111, 332-3 (1950)], an elastic band method and a geometric proportional divider called a partogrid. A simple scale has been developed in this laboratory which eliminates the measurements and computations involved, and enables an accurate direct reading of Rf values. It is believed it will find application in other laboratories. Two general types of scales have been used, both based on the same principle. The simpler one involves the construction of a right triangle with the long and short axes equal in length t o the maximum and minimum height, respectively, of solvent advance to be used in different determinations. The long axis is divided
will serve to illustrate the method of constructing the scale, assuming several different chromatographic methods are used in which the solvent map be allowed to advance any distance between 2 and 18 inches. A family of one parameter curves is plotted in one quadrant of polar coordinate paper in which? varies from 0 to 1.0 by steps of 0.1 and e varies from 0” t o 90 . In this case, a is 2 and b is 16. Figure 2 shows the curves which result. -4reverse negative of a full scale photograph yields a very acceptable transparent scale.
For use, either scale is laid with its origin or the vertex of the right angle directly over the point a t which the unknown was placed on the chromatogram, and then rotated until its outer edge coincides with the solvent front directly above the unknown. The developed spots above the unknown are located under the transparent scale and the R f values may be read directly to the nearest one hundredth. The R f values of the various constituents in an unknovin can be determined and recorded in a feu seconds. Fewer errors are noted and the scale can be uscd by several workers with highly reproducible results.
