V O L U M E 2 5 , N O , 9, S E P T E M B E R 1 9 5 3 Thc action of the escapement, together r i t h construction principle?, i p shown in Figure 2. As in Figure 1, A is the disk, with pins, B, and C is tho fork of the escapement.. Pallet 1 of C must be filed or ground to present an a r c of a circle centered on screw Q to B; pallet 2 of C is less critical, but should he cut so a8 to engage B when the solenoid, S, is energized. S is wound on a glass tube, bent to form an arc of a circle centered on Q (armature P is also bent on this arc). 0 is soft iron, and ~ e r v to e ~complete the magnet,ic circuit.. R is stop pins to limit the movement of C. C, 0, and S are mounted bv means of vooden blocks on a wooden
to A , so that pallet 1 of C @events rotation of A &en the salenoid is inactive, and pallet 2 of C checks A on actuation of the solenoid and also restores pallet 1 of C to position upon deactivation of the coil. Weight I (Figure 1 ) and the voltage supplied to the solenoid are adiusted to eive reliable oneration. The authors' solenoid is wouid nzith KO. 26 enameled copper wire, and has a resistance of 34 ohms. When a weight of 94 grams is used,
The current supplied to the solenoid for actuation of eseapement is controlled by the timer shown in Figure 3. The timer is driven by a small rvnchronous motor, A , turning
1427 but it should be easy to increase the c;lpacit,y with only .z slight, increase in size of the escapement. LITERATURE CITED
(1) Baggs, L. A., Cuendet. L. S.. DuBois. M., and Smit! CHEM.,24, 1148 (1952). ( 2 ) James, A. T.,Martin, A. J. P.. and Randall, S. S., YYICIIIIII. .,., 49, 293 (1951). (3) Schroeder, W. A., and Core?. R. B., AXAL.CHEW..23, 1723 (1951). (4) Stein, W. H., and Moore. S.. J . Bid. Chem.. 176, 337 (1948).
Photoelectric Volume-Measuring Accessory. Herbert J. Dutton and Francis d. Castle, Nort.hern Regional Roscxreh Laboratory, Peoria 5, Ill. are frequent occasions when fractions of specified T"" volume between 5 and 20 ml. need to be collected auto,RE
matically. In many instances of chromatography, distillation and liquid-liquid extraction rates of flow may vary too greatly to permit the use of "tim4ow" mechanisms or may he too rapid for drop-counting mechanisms. The following apparatus may be assembled from parts readily available or constructed in most, laboratories. A "plug-in" method of connecting this From Column
1
The weighi of t,be 'glass fram&ork, axlei and &heel provides enough friction far the disk to drive the wheel. Wire E, cementid to the d e , turns mith it, and the two ends of E pass, once per revolution, through the mercury cups, F , dosing a circuit to actuate a relav IH-B relav Tvoe SS-5). modified to operate normally open).' -The relapin "(urn co&ols the current into % variable transformer, which supplies the solenoid.
6
A slightly modified timer of this sort has been operated reliably using a cheap spring-driven alarm clock to turn the disk. It should therefore be possible, by using direct current from storage batteries to operat,e the escapement, t o conduct fractionations completely independent of the ordinary building u t i l i t i e e which is a point of importance in regions vhere electrical supply is unreliable.
Figure 3
A schematic repmsmtntion of this aceesso~yis given in Figure 1.
This fraction collector and timer was built a t a cost for parts (other than the relay and veriable transformer) of less than $10. Using only hand tools, a duplicate could he built by one person in between 2 and 3 days; if power tools for cutting the disks and the iron parts of the escapement mechanism were available, this time could be considerably reduced. The device has performed well and reliably, mainly for isolations. It should be readily adaptable to analytioal operations, as, a t the flow rates used, very little material is lost in drops while the distributor arm is moving from one receiver to another. The simplicity and cheapness of the appaxatus should recommend it to the smaller laboratory, or for isolation procedures generally. Its only drawback a t present appear8 to be its limited endurance-it would operate only 6 hours without attention if 10-minute fractions were collected-
A is a.light BOUTCB; B , a slit; and C, a photoelectric relay. A Fisher-Serfass photoelecbrie relay and a Worner Products relay have been used successfully. In general, photoelectric relays of high light sensitivity are preferable because they permit more leeway for narrowing the light beam, far using lower intensity light sources, et,c. D is a normally closed singlep$e, single-throw relay; E a normally open double-pale, smgle-throw relay; and F, 8. Christmas tree blinker. A button type which fits into a light socket was used, rated for 60 watts. G is a solenoid coil from a 110-volt mercury relay or solenoid valve, and H is a 60-watt light bulb. The glass float, I, is blaun to have thin walls and is silvered internally before sealing off. The reservoir, J , is constructed from a borosilicate glass 25-ml. Mohr pipet. At its lower end is ground a surface to seat a steel ball bearing, K . This surface is.ground with the aid of silicon carbide and a hall bearing of t,he size of K , welded to B steel rod and rotat.ed in a Inthe.
ANALYTICAL CHEMISTRY
1428 OPERATION
The sequence of events completing one cycle is as follows:
switch which is fo&d inside thk collector and is operated by a cam driven by the motor. This switch, in closing, actuates double-pale relay E. One pole of the reley Serves to “latch in” the relay; the other pole opens the solenoid valve to drain the reservoir and to apply current to the heater of the tbermoswitch or Christmas tree blinker. During the heating phase of the thermoswitch, approximately 5 seconds depending on the siee of bulb used, the motor rotation completes moving up the new tube to receiving position and then opens the cam switch t o stoo the motor. the float is lowered, thus causing the ohato-
~
~
valve and cornpiit& the cycle. The volume delivered to each collection tube e m be set by raising or lowering the light source and photocell with respect to the reservoir tube. As all the electrical leads required are available a t the socket, L, on the Technicon collector, this aocessory can be connected and powered by means of a plug. No internal modifications of the collector are required; only a toggle switch located on the left side of the collector needs to be thrown t o use this accessory or to return the collector t o its normal time-flow operation. T m mention of products does not imply that they &re endorsed or reo-
during 8 to 24 hours. The two models (Figures 1 and 2) described have given excellent service during the pest 2 yeam in the course of methylation-structure studies on dextrans and determinations of the composition of hydro1 obtained in dextrose manufacture. The new features of these fraction collectors provide several advantages over previous designs. The use of continuous movement of the table, in contrast to the usus1 stepwise movement, minimizes the number of electrical and mechanical parts while retaining the use of an electrical drive. Limitation of the eleetrim1 component to a small synchronous motor eliminates the expense as well as the possibilities of failure of relays, timing devices, and escapements used in most fraction eallectors. Previously, continuous movement apparently had been used only with a moving effluent-distributor arm and stationary receivers poggs, L. A,, Cuendet, L. S., Dubois, M., and Smith, F., ANAL. CEEM., 24, 1148 (1952)l. The present movement of the table eliminates the long fragile didribntor arm and avoids diffieulties in maintaining its position relative to the circle of receivers. These advantages are particularly significant with a large table, mch as a 62-inch diameter table carrying 200 tubes, 16 X 150 mm., in the outer row. A gear drive, with several change gear combinations, provides positive movement of the table with selection from B wide range of periods of rotation.
ommended by the Department of Amioulture over others of Similar natnre not mentioned.
Fraction Collector with Continuously Rotating TurnraDle ana mproved Receiver Assemblies. R. J. Dimler, J. W. Van Cleve, Edna M. Montgomery, L. R. Bair, F. J. Castle, and J. A. Whitehead, Northern Regional Research Laboratory, Peoria,
Ill. chromatography has become a mo8t useful technique C for the separation of a wide variety of mixtures, for both qualitative and quantitative analysis. For the collection of OLUMN
fractions of the effluent, mechanical methods of diverting the flow from one receiver t o the next usually itre essential. As different performance requirements are placed on the fraction collectors by the various applications of column chromatography, a number of different designs must he available. Work with
For the collection of fractions, two simple and dependable arrangements were devised t o transfer the flow of effluent from the chromatographic column to the continuously moving test tube receivers without loss of solution between tubes. A navel feature of these two assemblies is the use of a glbfis insert in the test tubes, instead of a modified test tube, as a principal part of the control of the transfer from one tube to the next. As B result standard test tubes of unimpaired mechanical strength are used 8 s receivers. The inserts me sturdy and easily cleaned. The use of the inserts minimizes the number of special glass parts required, as the fractions can be retained in the test tubes during further examination while the inserts are transferred to new tubes. The cast of a fraction collector of this type is relatively low, The materials and parts, including the motor, for the driving mechanism cost ahout $30, and this can be reduced by using salvaged parts. The additional cost of the turntable itself will depend on its siee and material of construction. Turntable Drive Mechanism. A general view of the motor and gear box assembly used for driving the turntable is s h a m in Figure 3. Considerable variation is possible in the choice of
