The omission of the mineral oil results in low recoveries of the pesticides. Obviously, modifications of the basic evaporator design may be desirable, depending on the particular application. The block can be made larger or smaller to hold more or less tubes of greater or lesser capacity, For tubes of different diameters, holes of different size or shape will be required; or less liquid bealso, special tubes can be made to hold low the heating zone. A cartridge heater may be placed in one of the holes if additional heat is required. High temperature heating tape could be used instead of constructing a heater. The same principles applied here might be useful
with the Kuderna-Danish concentrator (3)-i.e,, use a heating mantle with a hole in bottom-to evaporate larger volumes of solvent to approximately 10 ml, which could then be concentrated further in the present device. The device should be useful for concentrating chromatographic or other fractions. RECEIVED for review December 27, 1966. Accepted April 10, 1966. Mention of proprietary Products is for identification only and does not constitute endorsement by the U. S. Department Of *griculture. (3) F. A. Gunther, R. c. Blinn, M. J. Kolbezen, and J. H. Barkley, ANAL.CHEM., 23, 1835 (1951).
Design and Construction of a Multipurpose Digital Delay Timer William J. Eider, Jr., and Peter D. Klein Dicision of Biological and Medical Research, Argonne National Laboratory, Argonne, Ill. AT PRESENT, there are no timers commercially available for controlling laboratory equipment in which a 4- to 24-hour interval can be set with a precision of less than 15 minutes. The need for such a timer became apparent in studies of isotopically labeled amino acids on ion exchange columns ( I ) , where it was necessary to divide the emerging peak into 20 or 30 fractions, each fraction representing 0.25 to 0.50 ml, collected at intervals of 0.5 to 1.0 minutes. Because the volume of buffer required to reach the start of the peak was never less than 100 ml, and often greater than 250 ml, collection of all the intervening fractions would have required a fraction-collector capacity which was 8 to 10 times greater than the capacity of existing available equipment. An alternative method was to bypass the column effluent through the halted fraction collector until the peak was about to emerge, and then to collect only those fractions which were required. This method presupposed that the delay interval could be specified with a precision equal to that of a single fraction, or about 30 seconds, for a period up to 15 hours. Such an interval timer has been designed; two of these timers have been incorporated into a single control unit to provide simultaneous control over the buffer pump and fraction collector. Figure 1 is a schematic diagram of the complete instrument. Timing pulses are generated every 10 seconds by a 6-rpm synchronous clock motor, M , which has a small bar magnet mechanically linked to its shaft. The field of the rotating magnet activates a magnetically sensitive reed switch, SW2 (Gordos magnetic reed switch MR 406, Allied Electronics), that pulses Sodeco registers, T2 and T3 (Sodeco registers, Landis and Gyr, Inc., 45 West 45th St., New York, N. Y.). The Sodeco register is an electromagnetic predetermining device that provides a visual digital readout and control in a single unit. At the end of a predetermined run, the counter actuates a contact that ends the operation. The counter can be manually preset from 1 to 9999. Depression of the manual reset push button returns the counter to its initial preset. Two models are available that have resolving times of either 10 or 25 counts per second, Push button, SW3, starts the timing sequence by applying (1) P. D. Klein and P. A. Szczepanik, unpublished work, Argonne, Ill., 1967.
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Figure 1. Circuit diagram of timer power to relays RY1 and RY2. Both relays control continuity through the driving power supply, and are serieslocked through both their own contacts and the predetermining register contacts. They also control power to the output circuits. As each register is pulsed, it counts down to zero from its preset digits, and then deactivates RY1 and RY2. The power control of these relays is now reversed. SW4 and SW5 are manual bypass switches for RYl and RY2. This design has the advantage of using a simple, rugged, reliable timing unit, whose basic time increment can be altered at will by substitution of the appropriate low rpm motor. The Sodeco registers permit the total interval to be specified as a multiple of the basic time unit by simply dialing the numbers into the register. The modular nature of the registers, together with a common timing impulse for all registers, permits the design of a wide variety of logic sequences in which each step is separated by a precisely determined, yet completely flexible interval. In use, the dual timer control unit has proved to be versatile in its application, simple to operate, and remarkably free of mechanical or electronic difficulties. Besides providing the desired time precision, it has effected considerable economy in the use of glassware and scintillation vials. RECEIVED for review March 6, 1967. Accepted April 28, 1967. Work supported by the U. S. Atomic Energy Commission. VOL. 39, NO. 10, AUGUST 1967
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