V O L U M E 27, NO. 4, A P R I L 1 9 5 5
so1
relative percentages of sulfide sulfur in the Light Mara and Heavy Mara of Venezuela, the Light Eastern and Heavy Eastern of Venezuela, and the Santa Maria Valley and Wilmington crudes of California. This method should prove valuable ih following the course of the isolation or concentration of aliphatic sulfides from crude petroleum by techniques such as chromatography and thermal diffusion, and should be helpful in characterizing crude petroleum prior to refinery operations. ACKNOWLEDGMENT
The authors wish to express their appreciation to the Multiple Fellowship on Petroleum sustained a t Mellon Institute by the
Gulf Research & Development Co., which has supported the work described herein, for permission to publish this material. LITERATURE CITED (1) Andrews, L. J., and Keefer, R. M., J . A m . Chem. Soc., 74, 4500 (1962). (2) Ball, J. S.,U. S. Bur. Mines, Rept. Inrest. 3591 (1941). (3) Blake, K. W., Winston, H . , and P a t t e r s o n , J. A., J . Am. Chem. Soc., 7 3 , 4 3 3 7 (1951). (4) Hastings. S. H., ANAL.C H E M . ,25, 420 (1953). (5) Hastings, S. H., and Johnson, B. H . , I b i d . , in press. ( 6 ) Hildebrand, J. H . , a n d Scott, R. L., “Solubility of Non-Electrolytes,” 3rd ed., p. 274, Reinhold, New York, 1950. (7) K a r r , Clarence, Jr., Weatherford, W.D., Jr., a n d Capell, R. G . , AN.4L. CHEM., 2 6 , 2 5 2 (1954). RECEIVED for review August 12, 1954. Accepted December 15, 1954.
Manual and Continuous Recording Attachments for the Beckman Model DU Spectrophotometer G. L. ROYER, H. C. LAWRENCE, and S. P. KODAMA American Cyanamid Co., Bound Brook,
N. 1.
and C. W. WARREN W a r r e n Electronics, Inc., Bound Brook,
N. 1.
The Beckman iModel DU spectrophotometer has found wide application in the field of visual and ultraviolet spectrophotometry. To reduce the time required to plot a spectral curve with this instrument, the authors built a manual plotting attachment which would record the data from the spectrophotometer directly on a plotting paper. This saves time but suffers from the inherent disadvantages of point-by-point plotting in that one can only obtain spaced points on the curve. The continuous recording attachment described in this paper has the advantage of giving a complete record of the per cent transmittancy at all wave lengths through which the instrument is operated.
T
H E Beckman Model DU spectrophotometer was first described by Cary and Beckman in 1941 ( 5 ) . Since that time about 10,000 instruments have been built for use in the field of visual and ultraviolet spectrophotometry. The authors believe this large use has resulted because, as stated by Gibson and Balcom (9) of the U. S. Bureau of Standards in 1947, “The instrument is capable of precise and accurate measurement of spectral transmittance or transmittancy.” The Beckman Model DU instrument was one of the instruments used by Haupt ( 1 0 ) of the Bureau of Standards for establishing an alkaline solution of potassium chromate as a transmittancy standard in the ultraviolet. This solution along with a Tropex neutral glass filter was used by Brode, Gould, Khitney, and Wyman (d), also of the Bureau of Standards, to carry out a comparative survey of Beckman Model DU instruments located in a number of cooperating laboratories. They report that, in general, the results show good agreement among the spectrophotometers. A paper by Caster (6) presents and discusses data on the variability in the Beckman Model DU spectrophotometer and refers to a number of publications which report the precision of both the instrument and the over-all analytical methods in iyhich the instrument is used. The performance of the Beckman Model D U instrument, as indicated by these reports and the
experience in many laboratories, has made it a required analytical tool for chemical research and process control. Its reasonable cost has also made it available within the budget of the average laboratory. Because of the wide availability of the Beckman Model DU, a number of systems for the automatic recording of spectral data which incorporate this instrument have been devised and described in the literature. Coor and Smith ( 7 ) have described an automatic recording spectrophotometer which gave high-speed recording of per cent transmittancy. This instrument was reported to have Lyorked satisfactorily for a number of years, but it has the disadvantage that the “correction device” is not readily adjustable. The Beckman Model D K recording spectrophotometer is based on the design originally made by Kaye, Canon, and Devaney (11) and Kaye and Devaney (12) of the Tennessee Eastman Co. With change in light sources and detectors and by a change in the Beckman Model D U Spectrophotometer itself, it is possible to cover the range of 200 to 2700 mp. Etzel (8) has also decribed a single detector split-beam automatic recording instrument nhich incorporated the Beckman Model DU spectrophotometer. Per cent transmittancy versus wave-length data have been recorded automatically in the region 205 to 400 mp with the hydrogen lamp as a source and 320 to 700 mp with a tungsten lamp as a source. Beckman ( 1 ) has described a means of recording for process control the per cent transmittancy a t a set wave length using the Beckman hlodel DU spertrophotometer as a source of monochromatic light. Cahn and Gale have described ( 4 )the Beckman automatic operator, which can be attached to the Beckman Model DU spectrophotometer to produce point-by-point plots. The time for obtaining a normal curve of 22 points is about 3 minutes, and for a curve of 400 points about 60 minutes. The Model D U spectrophotometer can also be used for manual operation by the usual procedure. Recently, Muller ( 1 4 ) described the Process and Instruments recording spectrophotometer which a,lso incorporates the Beckman Model DU monochromator. A tenfold increase in resolution and low scattered light over the
ANALYTICAL CHEMISTRY
502 manual operation is claimed through the use of a photomultiplier. Curves can be drawn a t speeds of S to SO minutes for the spectrum of 215 to 700 mg. The apparatus referred to above indicates the importance of tools of this type. In this article two attachments are described, which have been built and found useful in the authors' laboratories. MANUAL PLOTTING ATTACHMENT
The relatively time-consuming nature of taking and iecording data from the Beckman Model DU led the authors to build a manual plotting attachment (3) which would record the data from the spectrophotometer directly on plotting paper as soon 8s the halance was obtained. Figure 1 shows a photograph of the attachment as combined with the Beckman Model DU. Figure 2 shows the same instrument with the cover removed.
Figure 3. Detail of cam meehaniam of manual plotting attachment
Bs1.000 CM. to30 M6.A.
'
.
'...,.,.. . :.n , . . ..
.'
!
250
350
WAVBENGM MILLIMICRONS
Figure 4. Ultraviolet spectrum of chromotrnpie acid in 0.1N hydrochloric acid plotted by manual plotting attachment
Figure 1. Manual plotting attachment combined with Beckman Model DU spectrophotometer
the usual case when the data. are being recorded for later use. In actual practice, the wave-length paints which are taken are dictated bv by the comdexitv complexity of the mrve curve hrine being menrlmd. measured, the choice of wave-length soacine: being made bv the ooerator who ~~
~
~
~~~~~~
~~
. ~~ ~.. ..~.~~~ ~
eter. B y m e a n ~of cables this is coupled to a cam mechaniam shown in the upper right of Figure 2 and then to the horizontal
tion of the usefblness of the log absorhsncy typeof plot can 6e found in the hook by Mellon (18). In operating the manual plotting attachment, the instrument is balanced in the usual manner employed with the Beckman Model DU. After proper balance has been obtained, the pushbutton switch mounted on top of the cover just to the right of the transmittance knob is closed momentarily. This excites a
not necessary t o adjust (he d i d of the spectrophotometel precisely to a given wave-length value before each reading, as is
Figure 5. Over-all view of continuing recording instrument with Beckman DU monochromator in position
V O L U M E 27, NO.
503
4, A P R I L 1 9 5 5
__
m ,
sm"aU,IFID
___
Bolenoid which causes the pen to strike the plot5 mmz Ilmr, a*."* II *."> s i * 10 Ejla ..,a ting paper, thus marking a dot on the paper a t the proper wave-length and transmittancy m_l.t:, values which correspond t o the settings of the wavelength and transmittance dials of the instrument. The wave-length knob is moved to the next position, balance is carried out, and the next point is recorded. This is continued until enough points are obtained to produce B spect r d curve over the range desired. This attachment does not shorten the time necessary t o balance the spectrophotometer, but it eliminates the time for reading bath wave-length and transmittance scales. In addition, it has the Figure 8. Block d i a g r a m of ratio-recording system advantage that the spectral curve is obtained directly, platted with the log absorbancy ordinate which zllows for ready interpretation of spectral data. Thus considerable time is saved, and the data. do not W l r l IYII," have to be subsequently plotted by hand from the recorded transmittancy and wave-length values. Figure 4 shows the ultraviolet curve of chromotropic acid plotted by this manual attachment. The approximately 75 points were made m about 25 nunutea or about 20 second? per point. This point-by-pomt attachment was hulk inexpenslvely and ir finding considerable use in the authors' laboratories, since it has speeded up the recording of entire spectral curves plotted with an ordinate which is desired for use in spectrophotometry. ./.-
t
.il
:
"*/.,-
1/.,1*
ll"l.sE
CONTINUOUS RECORDING ATTACHMENT
Automatic continuous recording has many advantages over the point-by-point method of the Beckman Model DU or the manual point-by-point plotting attachment. It gives a complete record of the per cent transmittancy a t all wave lengths through which the instrument is operated. I n view of the advantages, one of the authors (C. W. Warren) proposed the general optical and electronic layouts of an automatic attachment and several physical modifications have been built in the American Cyanamid hborittories a t Bound Brook. I n t h k paper the authors' latest continuous recording attachment for the Beckman Model DU apectrophotometer is described from the point of view of eonstruction, operation, and performance.
- .*" ,"...._.", .L.Tr*
.L.lS*
"
Part No.
Deaoription
P a r t No.
Deecription
voltage hdjust 47 K 2500 ohm 20 watts (Ohmite Bro& D e d ) Ra 2500 ohm 20 watts (Ohmite Brodm Devil) Ru 2 K, 10 watts (Ohmite Brown D e d ) Rid 1 K, 10 watts (Ohmite Brown Devil) Ra 100 ohm, 10 watts (adjustable Ohmite) Ria 5G K Rzi 100 K Ris 100 K R I ~ 330 K Rm 150 K Ru 100 K Rm 120 K R I ~ 47 K RM 6 8 K Rs 500ohms 5wStts h Alden 446-5FH 5 amp. Fa Alden 440-5FH: ,/a smp. SWz DPST. on-05 SW, DPST. interlock S W . DPST. interloek PLx Cornish cord set
Ru Rn
chromator
I
Yll,Y."
Power CI
Figure 6 . Unit containing pbotomulti-
.O,D"
2 ]&F.%
Figure 9.
pliers, cell chambers, mirrors, and cylindrical shutter a t t a c h e d to end plate of mono-
,.El0
~
All resistors o.s.w*tt less otherwise specified.
+ lO%\.Up-
40-40 mid.. 450 volts (Mallory FP-238) C, 0.5 mfd., 600 volts (C-D P J GP5) C8 0.5 mid., GOO mlts (C-D P J 5P5) C6 30 mfd.. 350 volts (Mallow FP-135) Ca 30 mfd.. 350 volts (MsJlorv FP-135) C. 0.1 mid., 400 volts (C-D PJ-4P1) CI 1.0 mid., 1500 volts (C-D TJU-15010j Cs 1.0 mid.. 1000 volta (C-D TJU-10010) C. 1.0 mfd., 400 volts (C-D PJ-4W1) Cxo 1.0 mid. 400 volts (C-D PJ4wi) Clr 1.0 mid. 400 volts (C-D pwwi) VI 5R4GY V* BAS70 Vz lZAU6 V. 6 x 5 Vs OB2 Amperite 2x2 VI Viotoreen 5841 Vg 12AU6 Vu 5687 TI Sterling T-1378A T, Thordarson T22P.40 TI Stanoor PM-8418 TI Etanoor PM-8418 T. Stanoor PM-8418 CHI Chioam RC-12150 CRz Thoidarson T2OC53 8 1 CJS-324-CCT-K S, Amphenol 61-P AC reoeptack 8s Amphenol 61-F AC reoep-
v,
t d e
504
ANALYTICAL CHEMISTRY
CONSTRUCTION AND OPERATION
Figure 5 shows the over-all view of the instrument with the Beckman monochromator in position. The regular Beckman cell chamber H.V. and photocell compartment have been V2a V2b removed from the Model DU, but the Beckman hydrogen or tungsten source is retained. T h e s e p a r a t e monochromator portion without any electrical circuits of the Beckman Model DU was obtained for use with the recording attachment, but the attachment can be placed directly on the regular Model DU spectrophotometer, since the original electrical circuits are not used with the attachment. In GND placing the recording attachment on I t h e Model D U , o n l y t w o new B I S (-105V) mechanical connections are necessary. 0 0 TO - O B V ( A D J U S T ZERO CONTROL) SIG.CUT The wave-length drive is connected to the wave-length knob and the slit drive to the slit knob on the Beckman OCFIL.(lS V D C I Xlodel DU. The cell chamber and photocell compartment of the original Model DU are removed and instead Figure 10. Signal amplifier for ratio recording system there is attached to the monochroPart No. Description Part No. Description mator end-plate a unit containing the p h o t o mu1t i p l i er s , c e l l chambers, 68 K RI Rle 10 K , 5 watts 120 K Ra Rl7 100 meg., 5 % (Victoreen) mirrors, and cylindrical shutter. This R,*ZiYK-10 watts Ea -I.~ is shown with the cover removed in 5 K, '10watts (Ohmite Dividohm) Rza 100 IC R4 Figure 6. Figure 7 is a schematic view 100 K R5 0.005 mfd., 200 volts (Gudeman XFHCI 1.2 K,2 watts 2535) Re of the instrument. R7 VI Electrometer tube (Victoreen 5803) Sample Cell and Detector CompartVz 12AU7 Re ments. The beam from the exit slit RQ Va 5879 FSi Fanning strip (C-J 7-160-A-R) R10 of the monochromator is interrupted 1P28 photomultiplier tubes (matched Rii a t 60 cycles per second in order to pair) E12 provide an alternating current signal Ria AlJ resistors k IO%, 0.5-watt unless otherwise RI4 for the electronic system. This beam specified. Rls is then split into sample and reference beams by means of a classical reflectance type of beam splitter which samples all portions of the beam for each of the two beams tiometer as required for balance. A rate generator coupled to the pen balance motor develops a feedback signal which is used into which it is split. It is folded into two parallel beams by two concave spherical mirrors. These two beams pass to stabilize the ratio recording pen system. A variable control in this feedback loop allows adjustment to suit the operator. through the reference and sample compartments which hold standard cylindrical-type absorption cells up to a maximum Slit Control. Continuous control of the slits of the monolight-path length of 10 cm. The holder could be readily adapted chromator to maintain signals of a reasonably constant level from to the use of the square 1-cm. cells if desirable. The beams the photomultipliers through the wavelength region being then fall upon selected IP28 photomultiplier tubes which are scanned is accomplished automatically by the slit servo. The reference signal is compared a t the slit summing amplifier with mounted integrally with their associated voltage dividers and amplifiers. The Model DU spectrophotometer can be removed a constant reference voltage, the slits being opened or closed by readily and be reassembled with the regular Beckman accessories the slit drive motor as necessary to maintain the ratio between for other uses since no changes were made to the spectrophophotomultiplier signal and reference voltage reasonably contometer. stant. Varying the reference voltage potentiometer varies the Ratio Recording. Ratio recording is accomplished by a slit width and provides control of resolution. An over-all control of sensitivity is obtained by varying the high voltage supply to unique circuit for which patent claims have been allowed (16). the photomultipliers. Figure 8 shows a block diagram of the recording system and Figures 9, 10, and 11 are the diagrams and parts lists of the Recording Platen. The recording platen is mechanically power supply, signal amplifier, and pen or slit servo-amplifier, connected to the wavelength knob of the Beckman monorespectively. In the system under discussion a portion of the chromator through cable drives and is driven by a continuously reference signal is added to the sample channel as necessary to variable-speed motor. While any wave-length range can be raise the sample channel level to equal the reference channel. chosen, it was decided to standardize on two, one covering 220 At zero per cent transmission all of the reference signal is used to to 385 mp and the other 300 to 750 mp. oppose itself to raise the sample channel to the reference channeI Adjustment of the Zero and 100% T Lines. The level of the level and the noise in the reference channel cancels because of zero line is adjusted electrically by means of a potentiometer the opposite sign. The signal from the reference amplifier is fed control. The adjustment is made with radiation falling on the reference photomultiplier only, the shutter in the sample t o the summing amplifier and also across a balance potentiometer which is connected to the recording pen and pen drive motor. beam being closed. The zero line has been found to be stable a t the level a t which it is set. The differential compensator attenuates the sample signal and consists of a single potentiometer with two mechanical inputs The level of the 100% T line is also adjusted electrically by arranged in differential fashion. One input is from an adjustthe balance control potentiometer with radiation falling on both able cam which is traversed by the wave-length drive. This insample and reference photomultiplier tubes. The position of put controls the flatness of the 100% line by compensating for the 100% T balance point was found to be stable a t the level spectral differences in detectors and mismatch of cells. The to which it is set. The lOOyo T line can be made straight over other input is a manual control which applies a bias to the anguthe entire spectral range bv means of the adjustable cam differential compensator. The differential compensator cam is conlar osition of the potentiometer body t o raise or lower the overall Eve1 of the 100% line. This input is called the balance connected to the wave-length scanning mechanism. The adjusttrol. A portion of the reference signal is then added to the sample able cam consists of a flexible metal band which is backed up by signal by the balance potentiometer, and the sum is fed to the screws which can be adjusted to determine its shape. These summing amplifier. If, a t this point, the sum of the sample screws, which can be seen along the back of the platen in Figure 5 and along the front of the platen in Figure 7 , are adjusted a t signal plus part of the reference signal does not equal the refereach of these wave-length settings to give a correct 1 0 0 ~rending o ence signal, the pen motor drives the pen and balance poten-
1 5 -3
V O L U M E 27, NO. 4, A P R I L 1 9 5 5
505
VI-
V8b
v2n
V2 b
,
slowest speed gives a complete ultraviolet spectrum in approximately 14 minutes. Scanning speeds outside this region can be obtained by changing the scanning gear ratios.
i
OUT v3n
I
V3b
Bt(t2X)V)
CHASSIS
GND
PERFORMANCE
ADAPTER
Resolution. The resolution of the recording attachment was observed by measuring benzene vapor a t the increasingly narrow slit widths R-hich are possible as the photomultiplier dynode voltages are increased. Figures 13, 14, and 15 present three curves of benzene vapor recorded with mechanical slit widths of 0.3, 0.1, and 0.033 mm. at 250 nip. The slit widths at other wave lengths are shown in Table I. The slit widths of 0.3 mm. used in Figure 13 are representative of the smallest slit used within the workable sensitivity range of the normal Beckman photocell operation. Figures 14 and 15 show curves for increasingly narrower slits which are possible with the use of photomultiplier tubes. The secondary absorption peaks on the side of the main absorption bands definitely become resolved at the narrower slits. illso, as the slits are made narrower, the intensity of the narrow absorption bands is gradually increased. The limit of the resolution of Beckman monochromator in the ultraviolet region appears to be easily approached without an excessive noise level.
PLUGS
Figure 11. Pen or slit servo-amplifier for ratio recording system Part No. Description RI 1 Aleg., 1% (IRC-DCF) 1 hleg., 1% (IRC-DCF) R2 R3 68 K, 1% (IRC-DCF) 47 K, 1 % (IRC-DCF) R4 R6 680 K 180 K Rs Ri 10 K (IRC Type Q) (phase) l K R8 Ra 500 K (IRC Type Q) (gain) 47 K, 1 watt Rio 27 K , 1 watt Rii 390 K RL2 10 K (IRC Type Q ) (Tach) El3 1 Meg. R14 22 K , 1 watt R16 100 Ii Ris 100 K RII 10 K , 1 watt Ria 2.7 K Ri B 680 K Rzo 100 K R21 500 Ohm, 5 watts Rzz 1 K Rr3
All resistors & l o % , 0.5-watt unless otherwise specified.
Part No. Description 220 Ohm R24 1 K R16 1 Meg. R26 22 K R27 2 7 Meg., 5% R?E RES 150 K a . 15 Mfd, 450 volts (Mallory FP-343.5) C1 b. 15 Mfd., 450 volts (Mallory FP-345.5) e 40 Mfd 95 volts (Mallory FP-345.5) a: 20 Mfd:: 1450 volts (Mallory FP-426) CZ b. 15 Mfd 450 volts (Mallory FP-426) c. 20 Mfd:: 25 volts (RIallory FP-426) d. 20 Mfd., 25 volts (Mallory FP-426) 0.1 Mfd. c3 0.1 Mfd. C4 0.01 Mfd., 1% C6 0.01 Mfd., 1% Ca 0.5 Rlfd. C8 0.01 Mfd. Ce 0. i Mfd.ClO 0.5 Mfd. c 1 1 11-Pin plug (Amphenol 86RCP-11) P1 8-Pin plug (Amphenol 86CP-8) Pz 8-Pin plug (Amphenol 86CP-8) Pa 12AX7 Pen service, 12AU7 slit service VI 12AX7 Pen service, 12AU7 slit service V2 v3 5687
under any desired cell conditions. As the instrument scans through the wave-length range, the follower on the adjustable cam actuates the differential compensator potentiometer, so that the balance point is maintained at 100% T over the entire spectral range being scanned. A 100% line which was flat to z t l . O % 2’ cnn be plotted even with mismatched absorption cells in the sample and reference beams as shown in Figure 12. While this rompensator accomplished the results shown in Figure 12, it was difficult to adjust and for routine laboratory use electrical compensation might be more desirable. Scanning Time. The ultraviolet region from 220 t o 385 mp can be scanned in a continuously variable range of speeds. At the fastest speed, the scanning time is 1 * / 3 minutes, while the
100:
o
, 270 265
I ‘“t
TI
, 260
Figure 13.
255 250 245 240 WAVELENGTH MILLIMICRONS
235
230
Spectrum of benzene vapor
Recorded with mechanical slit width of 0.3 mm. a t 250 mr
Table I.
- i t 0
I
Slit Width Settings
Wave Length
Figure 8
270
0.23
260 250
240 230
0.26
0.30 0.37 0.48
For Curve on Figure g 0.080 0.085 0.10 0.12 0.17
Figure 10 0.024 0.099
0.033 0,040
0.053
506
ANALYTICAL CHEMISTRY
Linearity of Photometric Scale. .4 series of National Bureau of Standards calibrated gray glass filters was measured a t a wave length of 530 mp. Table I1 presents the comparison of the measured values with the calibrated values for each of the twelve filters or combinations. These data confirm the linearity of the photometric scale.
Table 11. Photometric Scale Checked with Neutral Gray Filters Value Found
Calibrated Value 2.0 3.8 7.1 10.0 19.1 26.5 30.3 37.0 41.2 52.2 55.8 71.4
,
01
270 265
Difference
260
,
Figure 15.
255 250 245 240 WAVELM"S MILLIMICRONS
235
230
Spectrum of benzene vapor
Recorded with mechanical slit width of 0.033 mm. at 250 mu
-LLD
Iw-
-
lo-
-
Stability during Continuous Operation. The balance point
at 100% 5" was found to remain fixed within =t0,5% during 18 hours of continuous recording a t a fixed wave length of 300 mfi with air in the sample and reference beams as seen in Table 111. As was shown in another test the balance point is little if any affected by line voltage changes as great as 30 volts or by small frequency changes. It is believed that the relatively small variations which occurred during the continuous operation test are more likely to be due t o changes in ambient temperatures. Reproducibility. The reproducibility of plotting a spectrum was checked by the use of the ultraviolet curve of benzene in iso-octane solution. The ultraviolet curve was plotted on the
-Lo
-
;3 0 -
f
UI-
-
-
-
I I I I I I
;',,,ww
Mc
,x
s o IO
I
,m
I
*a
I I I I I
tw In
no
le0
1 111
1
=
1
I.,
1
tUI
I 235
I
*XI
I 121
same plotting paper repeatedly, first a t slow and then a t fast scanning speed. The slow speed was at the rate of 14.5 minutes for the ultraviolet range of 385 t o 220 mp, while the fast speed was 2 minutes. The curves were found to be superimposed over each other within the width of the pen line, or approximately 0.1% T as shown in Figure 16, which shows that the instrument can be operated satisfactorily a t high speeds. LITERATURE CITED I
OY!'
265
260
235
255 250 245 240 WAVELENGTH MILLIMICRONS
Figure 14.
Spectrum of benzene vapor
Recorded with mechanical slit width of 0.1 mm. a t 250 mp
Table 111. Continuous Stability Run Hours 0
2 4
6 8 10 12 14 16 18 Maximum variation
%
Transmittance 100.0 99.8. 100.1 100.4 100.5 100.3 100.4 100.2 100.2 100.0 i0.5Yo
230
Beckrnan, -4.O., Brown Instrumentation, 1 , 16 (1945). Brode, W. R., Gould, J. H., Whitney, J. E., and W y m a n , G. M., J . O p t . SOC.Amer., 4 3 , 8 6 2 (1953). Butler, G. D . , and Lawrence, H. C., patent applied for. Cahn, L., and Gale, G . , Symposium on Molecular Structure and Spectroscopy, J u n e 1953, Columbus, Ohio. C a r y , H . H., and Beckman, A. O., J . Opt. SOC.Amer., 31, 682 (1941). Caster, 77'. O., A s . 4 ~ CHEM., . 23, 1236 (1951). Coor, T., Jr., and Smith, D. C., Rev. Sci. Instr., 18, 173 (1947). Eteel, H. W., J . O p t . SOC.Amer., 43, 87 (1953). Gibson, K. S., and Balcorn, AI. SI., J . Research Satl. Bur. Standards, 38,601 (1947). H a u p t , G. W., J . O p t . SOC.Amer., 42, 441 (1952). K a y e , W., Canon, C., and Devaney, R. G . , Ibid., 4 1 , 658 (1951). Kaye, W., and Devaney, R. G., Ibid., 42, 567 (1952). Mellon, hI. G., "Analytical Absorption Spectroscopy," pp. 104, 307, Wiley, S e w York, 1950. Mtiller, R. H., ASAL. CHEM.,25, KO.7, 2 3 9 (1953). Warren, C. W,, patent applied for. RECEIVEDfor review February 16, 1954. Accepted January 3, 1955. Presented before the Division of Analytical Chemistry a t the 124th Meeting of the A M E R I C h x CHEMICAL SOCIETY,Chicago, 111.
