AIDS F O R THE A N A L Y S T The siphon was suspended from one end of a balance beam equipped with two small mercury mitches near the pivot and a counterbalance a t the other end. S n additional weight perpendicular to and above the mid-point of the beam Tas used to raise the center of gravity, thus placing the balance in metastable equilibrium. To maintain the siphon in vertical position the siphon holder \vas pivoted. I n operating the unit,. the posit,ion of the counterbalance is adjusted so that the siphon arm of the balance tips downward when the siphon is half full. (In practice 1 drop of solvent is sufficient to put the balance in either extreme position, its swing being limited by mechanical stops.) I n the downward position the motor circuit is closed. The motor turns two cams; one indexes the table by engaging pins projecting from it, and the other cam closes the microswitch momentarily. Closing this microswitch circuit even momentarill- is sufficient to break the motor circuit, thus stopping the motor. This circuit is kept open by means of the mechanical catch within the latch relay until the siphon empties and the balance beam tips upward. This operation disengages the catch and the motor circuit is simultaneously closed within the relay and opened within the mercury switch on the balance arm to revert to the initial starting conditions. The motor indexes the table one tube only when the siphon tips downward.
Constant-Volume Fraction Collectors J. W i l f r i d Hahn and Melvin Nyman’, Rheumatic Fever Research Institute, Northwestern University Medical School, Chicago, 111.
of the column chromatogi aphic separation of D urinary . studies steroids inexpensive fraction collectors were needed URISG
to collect definite volunies of solvent. As a siphon constructed with an air escape vent (4)gavr vel!- good reproducibility (in a typical case, the volume of hrnzene determined by six weighings was 6.05 =t0.01 nil.) it was decided to use this as a basis for the modification of a tinier-actuated collertor (manufactured b!C . R. Stryker, S o r d k , Conn.) ahead? in use in the laboratory and the conPtructjon of a photoelectricall)- cbontrolled collector. The modification of the timer-actuated collector to deliver constant volumes is offered as a general solution of this prohlem for collectors that require hut a single impulse to index the table. T h e second collector was constructed on the basis that more light is transmitted across glasP tubing fillrd with solvent than empty tuhing . GRAVITY-.~CTI~ATEl) COLLECTOR
A lower limit of volume of about 1.5 ml. appears to be necessary for successful operation of this equipment. This limitation may be serious where microanalytical procedures are necessary. The minimum volume seems to he determined by the mercury switches and by frictional forces in the ball bearing employed as a pivot. This disadvantage can probably be minimized by the use of corrosionproof pivot points and by replacement of the mercury switches by a photoelectric cell arrangement to indicate t,he posi-
The addition of a latch relay and a siphon on a balance arm to t h e motor-driven turntable of the tinier-actuated collector modified the apparatus to provide for constant volume collections (Figure 1). The principle used is essentially that described by Brimley and Snox ( I ) , Chapon ( 2 ) >and &der and Alader ( 6 ) . Certain modifications of a mechanical and electrical nature have been adopted to ensure ruggedness of the instrument, reasonable sensibility, a free interchange of aiphoiis, and safe operation in t h e presence of flammable solvents. The use of hall bearings in place of knife-edges for pivots by kinematic principles provides for movement of the balance arm and the siphon in the desired plane of motion with very little friction and considerable ruggedness. 1 Present address. Southwest Foundation f o r Research a n d Education. San Antonio, Tex.
Figure 2. Y.
Figure 1.
H.b.
Schematic diagram of gravityactuated collector
B. CI. C1.
C8.
ca. c;, Cs , C6.
A . hlercury switches, microswitch B . Counterbalance weights C . Potter-Brumfield latch relay D . Siphon E . Motor F . hfotor s h a f t G . Ball bearing pivots H . Snap action microswitch J. Pins projecting from table K . Test tube rack P . Cam
E.
FI.
Fz.
L1, Lz. Pi.
PZ.
RI.
Cs.
Electronic circuit for optically controlled collector
Battery, 22.5volts 15 mfd., 150 volts. elect. 0.1 mid., 200 volts 1 mid., 200 volts 10 mfd., 150 volts, elect. 2 mfd. 200 volts Mazd~flaslilightbulb P R 6 Selenium rectifier Mallory 6S100 Selenium rectifier Federal 1002 Relay, Potter-Brumfield LhfJ, 10,000 ohms Potentiometer I R C 11-139, 2 megohms Potentiometer I R C 11-143, 10 megohms 2700 ohms (all 0.5watt)
330
Rz. Ra, Rij. R4. Rr, 1 1 1 2 % Ria. R6, Ri. R8.
Rs.
RlO. Rii. R14.
Ti. T2. VI.
Vz .
vs. Va .
1 megohm 10 megohms 240,000 ohms 0 5 megohm 100 ohms 150,000ohms 3 megohms Transformer, Sola 30498 Transformer, U T C S 54 FSL7GT 12SH7 5692 lPJ2
V O L U M E 2 7 , NO, 2, F E B R U A R Y 1 9 5 5 tion of the balance, a system which would not interfere with the h l a n c e properties of the beam itself. OPTICALLY-CONTROLLED COLLECTOR
I n the second collector the same type of siphon was employed. Instead of using the weight of the solvent and the movement of :t balance arm to initiate the action, the siphon was fixed in a position so that the delivery arm interrupted a light beam impinging on a phototube. Because the siphon is fixed, provision can be made to minimize evaporation of the solvent by the technique of Mader and Mader ( 7 )or under more serious conditions by the use of refrigeration coils. When the siphon delivers, and solvent passes through the delivery tuhe, more light is transmitted onto the phototube. This effect, suitably amplified, energizes a solenoid-ratchet device to turn the table (Figure 2). Intensification of the light which falls on the phototube, V-4, makes the control grid of VO more negative. This causes the potential a t b and correspondingly at d to become more positive, permitting a fiow of current through one half of the 5692 h b e . 7’3, to close the L3fS relay, L1. With the relay closed, grid f of the other half of the 5692 tube is now connected to the positive power supply and current flows through the tube to close relay LOand consequently energize the electromagnet, S . The electromagnet is maintained in this condition as long as liquid is passing t,hrough the delivery arm of the siphon and for an additional time (to alloiv complete drainage of the solvent) determined by the R-C con&nt,s of the syst,em, Cs, C,, GI,, Rls.Iflr, and PO, through which the grid is grounded. The time delay can be varied by adjustment of PO. Final release of the electromagnet causes a spring-driven mechanism similar to that described by Schram and Bigwood (8) t,o rotate the table to its nest position. Pl is adjusted by trial and error with the siphon in posit,ion, so that the presence or absence of solvent, will determine the opening and closing of relay L,. The circuit described is essentially that of Johnson ( 5 ) . I t has been modified by the addition of the 6SLiGT tube, VI, n i t h its own separately biased grid potential as a “caseode” amplifier (3), t o provide a constant load for the 12SHi tube with a result,ant increase in gain and stability. The system works very well in this case, where the relays must he operated by small differences iri light intensity relative to the light levels used. It was not necessary to change the settings during 6 months when the collector \vas in nearly constant operation. ACKh-OWLEDGXIENT
The expense of this investigation was covered by a grant from The Helen Hay Whitney Foundation, which is gratefully acknoivledged. LITERATURE CITED
Brimley, 11. C . , and Snow, -\. J., J . Sci.Iustr., 26, 73 (1949). (2) Chapon, L., Bztll. SOC. chim.,1952, 53s.
(1)
Gray, J. W.,“Direct-Coupled ;iniplifiers.” in “Vacuum Tube .%niplifiers,” Vol. IS, Radiation Laboratory Series, L. S . Ridenour, ed., p. 439, RIcGraw-Hill Book Co.. Kew York, 1948. ( 4 ) James, d.T., Martin, A . J. P., and Randall, S. S., Biochem. J . , 49, (3)
293 (1951).
Johnson, Marvin, University of Wisconsin. private communication. (6) l l a d e r . C., and l l a d e r , G., ASAL.CHEIZ..25, 1423 (1953). ( i )Ihid.,p. 1556. (8) Schrain, Eric, and Bigwood, E. J., Ihid.,25, 1424 (1953). (5)
Fermentation of Sugars by an Ultramicrotechnique Prior to Paper Chromatography Kenneth T. Williams and Arthur Bevenue, Western Utilization Research Branch, Agricultural Research Service, U. S. Department of Agriculture, Albany 6, Calif.
authors, continuing work on the unfermentable sugars in T”” vegetahles [Killiams, K. T., Potter, E. F., and Bevenue, A ,
J . Assoc. O#c. Agr. Chemists, 35, 484 (1952)], have developed a technique for fermenting very small volumes of sugar solutions
331 with commercial baker’s yeast. h recent article liy Porter and Hoban on enzymatic hydrolysis [Porter, W. L., and Hoban, Xancy, ASAL. CHEJI.,26, 1846 (1954)] has prompted a description of the procedure as a further supplement to ult,ramierotechniques for paper chromatography.
h melting point t,uhe (1+ mm. by 100 mm.) was heated a t the center and drawn into two test tubes Jvith a head formed on the bottom of each tube. Medicine droppers were modified t)y drawing the tips to a capil!ary to fit easily into the micro test tubes. Holes a b o u t 2 mm. in diameter were drilled into wooden or metal hlocks to support the test tubes in an upright position. Small stirrers were made from draxvn glass rod. Three milliliters of acetate buffer and 8 ml. of 0.2M potassium tlihydrogen phosphate were included in 100 nil. of a 10% washtxd baker’s yeast suspension [Wi!liams, I
