attached to the apparatus. Khen equilibrium has been attained and the initial hydrogen volume is recorded, the sample capillary is broken by gently pushing the glass rod, B , against tlit: glass a.hic.ll exerts force agailist tile file inark arid ilreaks the capillary, The glass rod is al\vays \rit,hdra\vn to its original position, so as not to alter thr
initial hydrogen volume. The remainder of the hydrogenation is carried out in the conventional manner. This metliod of sample introchwtion wnrks very well for volatik samples that require a sample weight up to 30 mg. For volatile samples requiring a larger
sample size, introduction of the sample \Tith a hypodermic syringe works well. A gum rubber serum cap is placed over the stopcock opening and when initial equilibrium has been attained, the sample is inserted with syringe. The accuracy obtainable with this te.c.hnique is within 2%.
Two-Piece Centrifuge Crucible for Handling Microchemical Precipitates Cyrus Feldman and Janus Y. Ellenburg, Oak Ridge National Laboratory, Oak Ridge, Tenn. 7o
m of the operations in the isolation and treatment of a very small precipitate can seriously reduce analytical accuracy. If the precipitate is to be dried or ignited, considerable losses may occur in the transfer from centrifuge or filter to crucible. The danger of contamination, especially by common elements, becomes greater, the greater the amount of handling. If a precipitate is filtered on filter paper and ignited, the filter paper ash often contributes a blank of some elements greater than the amount originally present. It was felt that if a precipitate could be processed completely without changing containers, these losses and contamination would be greatly reduced or eliminated.
53
A device designed to make this possihle consists of a centrifuge tube which, after centrifugation, can be drained and separated into two parts. The lower part, which receives the precipitate, can be used as a container for drying, ignition, or dissolution. Leakage of liquid during centrifugation is prevented by the self-sealing action of centrifugal force on the beveled edge. A short rubber sleeve around the joint prevents accidental disassembly. The upper portion consists of a cylinder whose lower edge is beveled and ground. The lower portion has the shape of a crucible; its upper edge is beveled to fit the upper section. Its bottom may be flattened t o permit it to stand alone. A lid is provided to cover
the crucible during storage or ignition Before the device is used, ljoth beveled surfaces are coated lightly nith Silicone or Lubriseal stopcock grease. The pieces are pressed together and the joint is secured with a thin rubber sleeve. The centrifuge tube thus assembled is filled IT ith the liquid sample. After the wmplc has been rentrifuged and n ashcd, the supernatant liquor is decanted or drawn off until the liquid level is beloir the joint. The upper section is then removed. If desired, the remaining supernatant fluid can then be drawn off or evaporated, and the precipitate can be dissolved. dried, or ignited. The shape, size, and material of construction can be varied according to usage. The design shown fits a standard 50-ml. centrifuge cup. The models used in this laboratory are made from fused quartz, in order to permit ignition of precipitates in the crucible a t muffle temperatures. Glass. metal, plastic, or other materials can be used if thr subsequent treatment of the precipitate is to be less severe. The device was tested by dissolving a small quantity of acidified europium solution containing europium-154-5 tracer in approximately 50 ml. of water. This solution was transferred to the assembled crucible. Approximately 0.5 gram of sodium carbonate and 1.0 gram of sodium orthophosphate (XaoP0410 H L O ) w r t l thrn added and dissolved. The solution nas centrifuged immediately. The supernatant solution was then dtcanted, the sample n as naihed thrrc
Table I. Distribution of Europium-1545 Tracer after Centrifuging, Washing, and Drying To of Eu Tracer Found 1:u Taken, i
I00 10
In
In supernatant
pircipitate ‘19 0 95 2
qolution 0 0 4 7
times with water, and the washings were combined with the supernatant solution. The centrifuge crucible was then disassembled and the precipitate was dissolved in acid. The recovery of eurnpium-154 tracer was measured with a gamma ray scintillation spectrometer. Table I s h o w that this device permitq precipitates as small as 10 t o 100 y to be isolated from gram quantities of salts, in a form suitable for neighing or igniting, with little or no low.
Reduced-Scale Auxiliary Recording of Infrared Spectra Fred Stitt and Glen F. Bailey, Agricultural Research Service, United States Department of Agriculture, Albany 10, Calif.
R
produced by commercial, direct-reading recording spectrophotometers are rather bulky. The need for reduced-scale infrared spectral curves has been met using an recording system for producing reduced-scale curve simultaneousb with the standard instrument record ( 1 , 2 ) . This work describes a ECORDS
simple, convenient auxiliary recording system in use with a Beckman Model IR-3 spectrophotometer and adaptable for use with other instruments. A Varian Model G-10 recorder, 1second full-scale response, with the same range as the recorder of the spectrophotometer (50 mv.), is used to prepare the reduced-scale record. Because the
input resistance of the auxiliary recorder is high compared to that of the spectroa input photometer signal can be used for both recorders without significantly affecting the spectrophotometer record. Under these conditions the transmittance scale of the smaller record is 5 inches long. This scale can be shortened by increasing the input signal range of the auxiliary VOL. 29, NO. 10, OCTOBER 1957
1557
recorder, by reducing the input signal, or by reducing pen travel through use of smaller pulleys in the drive mechanism. The last of these methods was chosen to produce a 2-inch transmittance scale because the dead zone of the recorder is then proportionately reduced. In this way reducedscale transmittance readings are obtained which differ from those of the spectrophotometer record by not over 1%. The zero and calihratiou adjustments of the auxiliary recorder are used to adjust its transmittance scale to exact agreement with that of the spectrophotometer. Where the auxiliary recorder must also he used intermittently for other purposes, reduction of the input signal may he preferred to produce an auxiliary transmittance scale shorter than 5 inches despite the relatively increased dead zone. For this purpose a voltage divider of 50,000-ohm total resistance across the input to the spectrophotometer recorder was found to he sufficiently high to eliminate any effect on the original record. The chart drive shaft of the auxiliary recorder is connected hy a flexible shaft (automobile speedometer cable) and sear train to the chart drive motor shaft of the spectrophotometer. For this purpose 'a pinion gear inserted in the motor shaft drives the flexible shaft through a spur gear. The flexible shaft is connected to the auxiliary chart drive shaft through a Brown recorder chart drive gear train and simple friction clutch which are mounted on a base plate along with the auxiliary recorder (see figure). A choice of auxiliary chart wave length scales is provided by the change gears available for the gear train. Ample flexibility for swinging out the recorder chassis of the spectrophotometer without disconnecting the flexihle shaft is nrovided bv a IOODin the cable and holes'suitabiy Ideated $or passage of the cahle to the auxiliary recorder. A wave length scale of 0.5 inch per micron aud a 2-inch transmittance scale have been adopted for the reducedscale recordings. This yields a spectrum for the 2- to 15.micron region suitable in size for recording on IBM cards. The width of the pen trace limits the wave Y
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~
~~~~~
length accuracy of these records to about 0.02 micron and results in merging of peaks separated by less than 0.03 micron. The cards, containing a printed transmittance-wave length grid, are held by spring clamps against an alignment bar on a metalplate 5inches wide, one edge of which has regularly spaced slots cut to mesh with the teeth of one of the auxiliary recorder chart drive sprockets. This platen is pressed against an alignment bar fastened to the recorder by a spring-loaded idler wheel as indicated in the figure. The spring clamps simplify exact positioning of the wave length scale of the card on the platen. As the chart drive shaft of the auxiliary recorder is free to be turned forward but not backward, it is essential that the clutch he disengaged when the spectrophotometer chart drive is reversed in direction. The platen of the auxiliary recorder is easily positioned by hand, the platen being moved sidewise to disengage the edge drive slots when it is desired to move it backwards,
engage the clutch and flexihle shaft, r e move the platen and its alignment bar, and replae one of the two retaining plates which prevent the regular chart from becoming disengaged from the chart drive sprockets. Replacement of the pulleys of the pen drive mechanism may also he required if these have been changed. An anxiliary signal controlled hy coupling a potentiometer to the pen drive of the spectrophotometer recorder can be used as input to the auxiliary recorder for spectrophotometers in which an input signal suitable for direct auxiliary recording is not available ( 1 , $1.
In addition to employing readily available components, requiring comparatively little machine work, and providing flexihility in choice of transmittance and wave length scales, this anxiliary recording system permits the auxiliary recorder to be readily removed and used for other purposes when desirable. To do this it is necessary to dis-
11) Olsen A. L., Johnson, D. J., Pierson, ,R. H.,J . Opt. SOC.Arne?. 46, 354 (1956). 1 2) Strauss, F. B., Thompson, A. E., Chemistry & Industw 1955, 1402.
ACKNOWLEDGMENl
The authors wish to acknowledge the assistance of John Correia who did the machine work involved. LITERATURE CITED
~
MENTION of manufacturers and commercia1 products does not imply they are endorsedorrecommendedby theDepartment of Agriculture over others of & similar nature not mentioned.
Constant Rate Flow Device for Electrolyte Eluents in Column Chromatography Raymond K. Main, Leonard J. Cole, Leroy M. Bryant, and Stanley
K.
Morris,
Biologicol and Medical Sciences Division, United States Nova1 Radiological Defense Laboratory, Son Fronscisco 24, Calif. URING
investigations concerned with
D gradient elution column chromatography (8), a device was needed to control accuratelv the flow of eluent (an electrolyte lolution) through the column. This had to he capable of delivering a fixed volume of electrolyte (within the range of 3 t o 5 ml.) per hour, a t a constant rate, for periods of unattended operation up to 2 weeks.
1558
ANALYTICAL CHEMISTRY
The column material did not afford sufficientresistance to flow in some cases to limit the rate to that desired. Because the concentration of electrolyte was constantly changing in this instance, control devices based upon the principle of capillary throttle brought abont either by the use of a Mariotte bottle and capillary bore tubing (3, 4, 61, a partially closed glass stopcock, a Teflon
needle valve, or tubing packed with sized glass powder ( I ) , failed to control the rate of flow satisfactorily over relatively long periods of time.
The device, shown in Figure meets cons.ts the foregoing of a cylindrical, flat-hottomed glass vessel, A , provided with a small outlet connected by suitable flexible tubing to a capillary bore glass tubing gooseneck-
