Figure 2. Recorder trace of absorption of water vapor in atmosphere
:# PI
E
1K
5 K
dark current fluctuations by incorpor8tion of relatively expensive systems of light modulation, alternating current amplification, and rectification.
50 K
2% K
m
I
Rl
.R 5
T o Potentiometer or Recorder
Figure 1.
Detector circuit
PbS Cell.
Beckman R-92163, approx. 30,000 ohms, Beckman Instruments Inc., Fullerton, Calif. E. 1.5-volt No. 6 dry cells; larger E, with corresponding higher setting of resistor Pt, results in larger potential drop (signal) across load resistors Ri
p1.
PaSW.
RI
- R4.
-
Rs
Fine dark current control and measuring resistor, Helipot, 10 turns, 5000 ohms, Type A, and Duodial Coarse dark current control, Helipot, 10 turns 50,000 ohms, Type A, and Duodial Sensitivity control, rotary switch (nonshorting), 1 -circuit, 5-position Wire-wound resistors
a l-mv. recorder and a dark current bucking potential, E , of 9 volts. Despite the simplicity of the present system, the dark current changes only very slowly during a scan (Figure 2). Changes in the dark current are due to environmental temperature changes and are negligible a t the large slit widths and the correspondingly low sensitivity settings normally used for liquid spectra. Previous modifications (2-4, 6) have avoided the effects of
The cell and allied components, with the exception of batteries, are housed in a small box equipped with a shutter and with sensitivity range and dark current controls. The box is interchangeable with the phototube housing of the Beckman DU, so that the standard accessories (reflectance, flame, hydrogen lamp, etc.) may be used without modification. The long cell holder supplied with the Beckman D U is used with the PbS detector because longer sample paths are generally used in the near-infrared region than in the ultraviolet or visible regions. The tungsten lamp source of the Beckman DU is used with the PbS detector. A lens of approximately 30-mm. focal length mounted on the detector box concentrates the radiation in a small area (6). Use of the dials of Helipots PI and P p permits manual balancing with a potentiometer if a recording of the spectrum is not desired-e.g., for quantitative analysis at a fixed wave length. In the cell in-cell out technique, the difference in dial reading for the sample solution and the reference solution is proportional to the per cent absorption by the sample. Although the wave length scale of the Beckman DU is graduated t o only 2000 mp, rotation of the adjustment screw on the collimating mirror of the monochromator extends the range to about 2700 mp
W A V E LENGTH DRIVE
The wave length drive used for automatic scanning of spectra is a 3-r.p.m. Rodine motor enclcsed in a small cabinet and equipped with a worm gear. One or more drive gears are mounted on an extension to the vertical wave length scale shaft of the instrument. The motor cabinet is attached to the instrument by a single pin that projects from one corner of the cabinet through a shelf flush with the Beckman DU housing. Effectively the box is hinged by this pin, and a small coil spring maintains contact of the worm gear and the drive gear. Thus, the wave length scale can be rotated manually to the desired spectral region in a matter of seconds by applying sufficient force to overcome the spring tension. LITERATURE CITED
(1) Beckman Instruments, Inc., ANAL. CHEW29, 3A (December 1957). (2) Cahn, Lee, Zbid., 28, 141 (1956). (3) Coor, T., Jr., Smith, D. C., Rev. Sci. Znstr. 18. 173 (1947). (4) Kaye, 'Wilbur, J.' Opt. SOC.Am. 41, 277 (1951). (5) Kaye, - - - -Wilbur, - -. Spectrochim. Acta 7, 181 (1Y56-56). (6) Kaye, Wilbur, Canon, C., Devaney, R. G., J . Opt. SOC.Am. 41,658 (1951). (7) Waggener, W. C., J. Phys. Chem. 62, 382 (1958). I
. INFORMATION developed during work
under contract AT(07-2)-1 with the Atomic EnergV Commission.
Cell Arrrangement for Increased Utilization of Infrared Spectrophotometers in Process Studies C. E. Day, Polychemicals Department, E. t. du Pont d e Nemours & Co., Inc., Wilmington, Del.
N ADDITION
to application in batch
T analysis, laboratory spectrophotom-
eters are broadly useful for continuous analyses of gaseous and liquid process streams in semiworks and larger scale operations. Frequently a single instrument alternately monitors several components in one or more process streams. Determinations of major and trace components may require two or more sample cells of greatly different thickness to pbtain usable absorbances
for the analytical bands. Manual exchange of cells is time-consuming and inconvenient, leading to considerable lost instrument time. Two cells can be arranged in series to facilitate suchmeasurements. The figure shows a convenient scheme employed on a gas stream for analyses of components a t levels of approximately 50% and less than O.Ol%, respectively. A single-beam spectrophotometer (PerkinElmer, Model 112) is fitted with a
specially designed l-cm. cell and a 10meter, folded-path, gas cell (PerkinElmer, Model 127-1160) in series optically. Only minor adjustments are necessary to allow space for both cells and to achieve optimum optical alignment. Although transmission of the folded-path gas cell is lower than that of the l-cm. cell, the slit width of the spectrophotometer is easily adjusted to provide a satisfactory signal-noise ratio with relatively small sacrifice in resolution. VOL. 3 1 , NO. 9 , SEPTEMBER 1959
1605
,
The valves are arranged so that either cell can be flushed with dry nitrogen while the appropriate sample passes through the other cell. The intensity of the infrared absorption band (at constant wave length) indicates the concentration of the component and is recorded on the strip chart of the instrument. Background absorption is determined at the analytical wave lengths with nitrogen flowing through both cells. The usual precautions must be taken when a gas is polar and may be adsorbed on the walls of the larger cell.
SOURCE
MIRROR
ONE CENTIMETER
TOR
/ SAMPLE METER
The flexibility of this technique makes it widely applicable to multiple component analysis. The entire operation can be made automatic by using suitable timers and valves.
NITROGEN EXHAUST
SAMPLE NITROGEN
1
4
EXHAUST
I
Determination of Nitrogen in Uranium Nitrides Joan Lathouse,
F. E. Huber,
Jr., and D. L. Chase, Battelle Memorial Institute, Columbus, Ohio
interest was shown in deR termining nitrogen in UN and UzN3. A search of the literature reECENTLY,
vealed only a note (6) on the use of a modified Dumas technique, in which the sample is burned with exactly the right amount of potassium chlorate to give satisfactory results. This seems to indicate that a balance of errors might be operative, as a small excess of chlorate gave high nitrogen values while slightly less than optimum amounts gave lorn results. Therefore, it was decided to investigate various modifications of the Kjeldah1 procedure. Several digestion methods xere tried, using in all cases a sample ryeight of approximately 100 mg. Method 1. The sample was fumed with concentrated sulfuric acid. Potassium sulfate, copper selenate, and 30% hydrogen peroxide were added, alone and in combination. All these variations gave low nitrogen recovery on both UN and UzN3. Method 2. The sample was heated with 1 to 1 hydrochloricacid. Various amounts of hydrofluosilicic acid, hydrofluoric acid, and 30% hydrogen peroxide
Table I .
were added. Using 25 ml. of 1 to 1 hydrochloric acid, 1 ml. each of hydrofluoric and hydrofluosilicic acids, and 4 ml. of 30% hydrogen peroxide gave acceDtable results for UN. but low values for u ~ N ~ . Method 3. This was the Friedrich method ( 6 ) . which gave acceptable results for' CN. NiGogen recovery on UzN3 was more nearly complete than the previous methods, but still lower than the theoretical value. Recommended Method. The digestion mixture consisted of 1 to 1 hydrochloric acid with additions of copper selenate and hydrofluosilicic acid. Acceptable results were obtained on both GX and U2N3. APPARATUS A N D REAGENTS
DISTILLATION APPARATUS. The Parnas-JJ7agner (4) type was modified by addition of a n electrically heated steam generator consisting of a 2-liter reaction vessel with immersion heater, and a three-way stopcock placed betm-een steam generator and still. This allows the steam to be exhausted to the drain and the still emptied without interrupting the heat supply. The rest of the glassware is conventional laboratory equipment, and all
Per Cent Nitrogen in Uranium Nitrides
Method Sample
1 2.6
UN U4Na
2 5.5
No Samplewt decomposed sample Lot 2 Sample not 6.9 decomposed Values are average of a t least four determinations. Lot 1
1606
ANALYTICAL CHEMISTRY
chemicals are reagent grade. The sodium hydroxide solution is made up by dissolving 1.5 pounds of sodium hydroxide in 2 liters of distilled water, adding 0.5 gram of Devarda's alloy, and boiling until volume is 1.8 liters. The mixed indicator of Ma and Zuazaga ( 2 ) is used. PROCEDURE
Weigh about 100 mg. of sample into a 50-ml. beaker, and add 25 ml. of 1 to 1 hydrochloric acid and 1 ml. of hydrofluosilicic acid. Cover with a watch glass and heat just below boiling for 30 minutes. Add about 200 mg. of copper selenate. Digest until solution is complete. Transfer the cooling sample solution to the Parnas-Vagner still and add 25 ml. of sodium hydroxide solution. Distill and collect the condensate in a 50-ml. Erlenmeyer flask containing 4 drops of mixed indicator solution, with 5 ml. each of 4% boric acid solution and distilled water. Adjust the heat input by a variable transformer so that 5 minutes after distillation begins, 10 ml. of condensate will have been collected. The boric acid solution ('7) need not be accurately measured. Titrate the collected ammonia with standard acid (about 0.07N), and make a blank determination using the same amount of reagents as in the sample determination. RESULTS A N D DISCUSSION
5.5
Recommended 5.5
Theoretical 5.6
NO
8.3
8.1
sample 7.3
8.6
8.1
3
The preliminary work was performed on two samples of UzN3 and one of UN. The results given in Table I show that several digestion methods are suitable for analyzing UN. However, only the recommended procedure gives complete recovery of nitrogen in UzN3. To test the recommended procedures further two more samples of uranium
