of 12-mesh stainless steel gauze a t measured intervals, were inserted into the sample cylinder, which was then coupled tightly to the flange. The replacement inlet system was evacuated through the conventional mass spectrometer inlet system, then isolated by closing both Hoke vacuum valves. The transistors, whose locations within the sample cylinder were known from their positions on the wire gauze, were crushed bv squeezing the steel cylinder against the wooden block on which it rested, with a C-clamp. The strain produced by this action was insulated from the rest of the system by two retaining brackets and the flexible glass bellows. In use this system proved most satisfactory, permitting rapid interchange of samples, positive crushing of the samples, and freedom from leaks. After completion of the work, it was found that Norton [Rev. Sci. Instr. 26, 238 (1955)l had anticipated this design in a system used for sampling the gas in
fi
T R 4,N S I S T O R
A S S BELLOWS
.INDER
vacuum tubes. However, the system described here is superior to Norton’s in three ways. Most important, use of a stopcock and consequent selective adsorption by its grease are avoided. Second, this system permits simpler,
more rapid interchange of samples. Third, samples can be crushed and analyzed immediately, while Xorton’s required removal of the sample tube to a vise for crushing of the electron tubes contained n ithin the sample tube.
Modified Molecular Pot Still H. E. Ungnade, University of California, Los Alamos Scientific Laboratory, Los Alamos, N. M.
of the coniinercially molecular pot still designed by Hickman [Hickman, K. C. D., Sandford, C. R., J . Phys. Chem. 34, 637 (1930); Morton, A. A,, “Laboratory Technique in Organic Chemistry,” p. 120, NcGrarv-Hill, Xew York, 19381 has been used for some time in these laboratories. It has advantages over other modifications [Riegel, B., Beiswanger, J., Lanzl, G.. IKD.EKG.CHEW, AKAL.ED. 15, 417 (1943); Groves, K., Legault, R. R., AKAL. CHEM. 29, 1724 (1957)l. MODIFICATION
A available
cleaning of the equipment after distillation. Standard-taper ground joints are satisfactory for stills up to 70 mm. in diameter; spherical joints or flanges are preferred for larger stills. [A 3-inch demountable pot still with flanges is available from Distillation Products, Inc. (“Information on High Vacuum Distillation,” p. 5, Type MS4-5, KO. 8203).] The design of the vacuum line prevents the loss of distillate observed r i t h some commercial models. The smallest still (Figure 1) is used
3
The three most useful models of the molecular pot still vary in capacity from 0.1 to 30.0 grams, and in outside diameter from 20 to 70 mm. A larger and more uniform distilling surface is provided by use of a flat bottom (a flat disk is sealed into the bottom), controlled heating by a Dural block equipped with cartridge heater (J/sinch diameter Chromalox C-414A cartridge heater, E. L. Wiegand Co., 7500 Thomas Blvd., Pittsburgh 8, Pa.) for the small stills, and a Glas-Col mantle (Glas-Col Bulletin 4, p. 22, No. 0-592. 150 W-110 V) or a Dural block for the 70-mm. still. The disadvantages of the common commercial still (Fisher Scientific Co., catalog No. 111, p. 366, No. 9-124) have been overcome by use of a ground-joint cooling finger and a sharply bent vacuum line. Cooling surfaces which may be rotated and removed permit the return of distillate during the degassing phase, and 1 126
ANALYTICAL CHEMISTRY
k
69 mm
primarily for distillation of analytical samples. It is equipped with a Dural heating block 29 mm. in outside diameter and a receiver holding a screw-cap vial. The distillation temperature is estimated by a direct-reading tliermocouple which fits into the l/s-inch hole in the block just below the heating surface. The cooling finger has a clearance of preferably 1.5 to 2 mm. from the malls of the still, and is cooled by running water, ice, or dry ice. A further modification has been suggested (K.C.
--
~-
Figure 1.
Semimicro molecular pot still
Figure 2. Molecular pot still 36 mm. in outside diameter and larger
D. Hickman, Distillation Products Industries, Rochester 3, K. Y., private communication) which permits the distillate-collecting tube to rotate with the stopper, so that the receiving spout can be turned upside down n-hen required. The larger molecular pot stills (36
and
io
mm. in diameter) have a male
7 19/38 ground joint (Figure 2 ) for
a receiving flask or fraction cutter. When a heating mantle is used with the 70-mm. still, the distillation temperature can be estimated from a dial thermometer inserted between the mantle and the wall of the still.
The molecular pot stills have been particularly useful for the distillation of thermally sensitive substances such as nitro compounds. WORKperformed under the auspices of the U. S. Atomic Energy Commission.
High Resolution Infrared Ammonia Spectrum Wilbur Kaye, Beckman Instruments, Inc., Fullerton, Calif. SPECTRUM
of ammonia can now be
A obtained on a commercial instrument with a resolution, over portions
of the spectrum, exceeding anything that has been reported in the literature ( I , 4). Such a spectrum has been obtained on a Beckman IR-7 prism-grating spectrophotometer ( 2 ) . If sufficient path length is available, ammonia shows sharp absorption bands throughout the conventional rock salt region of the spectrum. Thus this gas spectrum can be used as a measure of instrument resolution by either examining the separation of closely spaced bands or measuring the half-band width of single isolated lines. I n the spectrum reported ( 2 ) the ammonia sample unfortunately contained a small amount of water vapor, whose spectrum became apparent in regions where ammonia absorbed weakly. Essentially all the bands above 3585 ern.' were due to water vapor. There were a few around 1400 and 1830 cm.-l Pressure-broadening effects were particularly noticeable in the spectrum. The width of the absorption bands a t approximately 1% of the maximum absorbance is greatly enhanced by pressure
effects, while the peak intensity does not appear to be so greatly affected. The instrument does not have sufficient resolution to measure true peak intensities of low pressure gases. Even a t a pressure of 7 5 mm. the base of the strong Q branch a t 965 cm.-' extended as far as 985 cm.-l The influence of ammonia molecules on broadening the water vapor spectrum was apparent a t 3622 cm The spectrum was scanned with relatively little operator attention. The scanning speed was adjusted so each panel was scanned in 24 hours. For low pressure runs the cell was refilled every day, because it leaked about 2 mm. per day. The monochromator was purged with dry air to eliminate the effects of atmospheric absorption bands. The cell was an adjustable path length multireflection 10-meter Beckman cell (3). Its optical efficiency depends on the number of internal reflections. -4screen was introduced into the reference beam to compensate for reflection losses in the cell. A maximum path length of 8.2 meters was used, because the reflection loss required to achieve
10-meter path length overcame the justification of the 22% increase in path length. A slit width schedule was used that yielded a single beam-double beam ratio of 0.5, which effectively increased the time constant of the filter to G4 seconds. Resolution mas limited by slit width in the region from 600 to 2000 cm.-l and by scanning speed from 2000 to 4000 cm. The particular presentation used was selected to fit into the existing order changes of the instrument (1100, 2000, and 3000 cm.-l). The frequency scale is believed to be accurate n-ithin the limits of easy readability. At a future date it is hoped that the frequencies of absorption bands can be tabulated with accuracy for frequency calibration use. LITERATURE CITED
(1) Barker, E. F., Phys. Rev. 55, 667-62 1103R'I. --, \ -
(2) Beckman Instruments, Inc., Data File L-56-39(1958). (3) White, J. U., illpert, Y. L., J . O p t . SOC AWL.48,460-2 (1968). (4) Kood. D. L.. Bell. E. E.. Sielsen. H. H., Proc. .Vatl. h a d . Sci. 36, 497-501 (1950). \
,
New Indicator for the Mercurimetric Chloride Determination in Potable Water Eugene Goldman, Sanitary Engineering Division, Los Angeles Department of Water and Power, Los Angeles, Calif. MODIFICATION has
been made in the
A indicator used in the mercurimetric
chloride procedure. A single measured addition of indicator allows automatic p H adjustment to the optimum range for most potable waters. The diphenylcarbazone end point is sharpened, resulting in a precise and more rapid method than those requiring colorimetric pH adjustment. The method is useful in field work. The indicator is prepared by dissolving 0.25 gram of crystalline diphenylcarbazone, 4.0 ml. of concentrated nitric acid, and 0.06 gram of xylene cyano1 FF in 100 ml. of 95y0 ethyl alcohol. This
reagent is not stable indefinitely. Deterioration causes a slow end point and high results; stored in a refrigerator in a dark bottle the indicator is stable for 2 months. Procedure. Use a 100-ml. water sample or smaller aliquot, so that the chloride content is less than 10 mg. When 1.0 ml. of indicator is added to 100 ml. of water, the color of the solution should be blue-green. A light green indicates a pH of less than 2.0; a deep blue indicates a pH of more than 3.8. For most potable waters the p H after this addition will be 2.5 i 0.2, found optimum for the titration. Titrate the treated sample with standard mercuric nitrate to a definite
purple end point. The solution mill turn from green-blue to blue a few drops from the end point. Determine a blank by titrating 100 ml. of distilled water containing 10 to 20 mg. of sodium bicarbonate. In standardizing mercuric nitrate, use replicates containing 5 to 10 mg. of sodium chloride and 10 t o 20 mg. of sodium bicarbonate diluted t o 100 ml. with distilled water. ACKNOWLEDGMENT
The author thanks C. S. Ung, Los Angeles Department of Water and Power, for laboratory work on the indicator.
VOL. 31, NO. 6, JUNE 1959
1127
