microns and 2.72 microns, corrected to 760 mm. us. grams of KzC03 per 50 ml. These are smooth curves. Analysis of Samples. Pipet 50 ml. of sample into the reactor flask and proceed as in the calibration. If the pressure release valve is activated during a n analysis, a smaller sample is run. I n t h a t event, the volume is kept constant by adding additional solvent or water until 50 ml. is reached. Correct absorbances t o 760 mm. by using the pressure-absorbance curves and determine grams of K2CO3 per 50 ml. by the calibration curve. DISCUSSION
CO, Generation as Function of Time. As the data of Table I indicate, the reaction reaches apparent maximum COZ formation in 5 minutes. Thus, a n interval of 5 minutes is the recommended minimal residence time in this procedure. G a s Flow Is Dependent on Proper Evacuation of Apparatus. It is important t o evacuate only that part of the system beyond the reactor flask, namely, the manometer, infrared cell, and associated tubing and connections. Should the reactor and separatory funnel be evacuated, the generated COz will not flow readily when value A is then opened. As part of the system is not evacuated, a partial pressure in the reactor due to air, water, and hydrochloric acid is common to the calibration and analysis. This partial pressure is 676 to 678 mm. registered when 20 ml. of 1 to 1 HCl are delivered into a blank sample. I t is not subtracted from standard calibration blends or samples. Calibration of the apparatus for CO, analyses over a specific concentration range minimizes such errors as solubility of the gas in the conhing liquid and variations in molecular volume. Sample pressures are corrected to 760 mm.
Table 1.
COz Formation a s Function of Time Absorbances at 4.32 p in Minutes 7.5-cm. cell
i.*L/
m a S Q m
I
ob
1 200
1 400
.
1
600
800
1000
PRESSURE, mm. Hp
Figure 2. Pressure-absorbance curves of generated C o t Curve A, at 4.32 p Curve B, at 2.72 I.(
by reference to the standard pressureabsorbance curves established in the calibration. Under normal laboratory conditions, temperature corrections are ignored. Accuracy a n d Repeatability. Carbonate analyses by the infrared method agree with those obtained by the gas evolution-absorption tube method (Table 11). At the 0.4yG KzC03 level in solvent, the one sigma repeatability figure is 0.04YG. This is based on 11 replicate analyses from one sample. The generation of COZ over an aqueous acid solution does not produce significant etching of the NaCl windows of the gas cells. After 250 analyses in the IR gas cell, the slight etching of the NaCl windows does not warrant any polishing of the plates. Applicability. This procedure has been developed for soluble carbonates. It has not been applied to those carbonates in natural mineral deposits, such as magnesite and dolomite, which are decomposed slowly by cold dilute acid (4). The apparatus will be used for measuring
a
0.25 0.292 2 0.532 5 0.620 10 0.620 15 0.629 20 0.639 30 0.623 0.302 g. of KzC03 per 50 ml.
Table II. Comparison of IR Method with Absorption Method for Carbonates KZCOI, Wt. % Theory Infrared Absorption 0.16
Unknown 0.80 1.06
0.22 0.81 0.90 1.10
0.22 0.78 0.91 1 06
gases generated in other chemical reactions. ACKNOWLEDGMENT
The author acknowledges the technical assistance of Francis T. FitzSimmons. LITERATURE CITED \
1) Loveland. J. IT..Adams. R. ,
W..Kine.
H. H., Sowak, F.’A., Cali, L. J.,’ANAI:
CHEM. 31, 1008 (1959). (2) Lundell, G. E. F., Bright, H. A.,
Hofmann, J. I., “Applied Inorganic Analysis,” Chap. 50, %ley, New York,
1953. (3) Pierson, R. H., Fletcher, A. N., Gante, E. S t . Clair, ANAL. CHEM.28, 1218 (1956). (4) Treadwell, F. B., Hall, W. T., “-4na-
lytical Chemistry,” Vol. 11, Chap. VIII, Wiley, New York, 1947.
Room Temperature Oxidation of Silicone High Vacuum Grease Robert H. Linnell, Harold J. Wimette, and Frederic W. Gross, Scott Research Laboratories, Inc., P. 0. Box 66, Perkasie, Pa. gas samples containing Ipounds low concentrations of organic comwe use a 40-meter pathlength N ANALYZING
absorption cell and a Perkin-Elmer Model 21 infrared spectrometer. Our 40-meter cell has a volume of 57 liters. We frequently find it convenient to sweep gas samples into this evacuated cell with either prepurified nitrogen or dry, COz-free air. Gas samples are collected in borosilicate glass flasks of 600- to 1500-mi. volume with a stopcock at each end. We have been using Dow Corning high vacuum grease on the stopcocks. It is stated that this grease is oxidation resistant and that the grease can be removed by rinsing with
kerosene and then cleaning with warm chromic acid solution. We have run into trouble with contamination of our gas samples and it has been definitely established that this is due to the reaction of chromic acid with the silicone grease. It had been our practice to clean our borosilicate glass sampling flasks by filling them with chromic acid cleaning solution (at room temperature), letting them stand a few minutes, flushing out the residual chromic acid with tap water, cleaning with Alconox, flushing with tap water, and finally rinsing several times with distilled water. Prior to use, each sample flask is evacuated to 50 microns
and filled with either dry, COz-free air or prepurified Nz and this procedure is repeated three times. After collecting a gas sample, the sample is flushed into the long-path infrared cell and the spectrum recorded. Bands appearing a t 3.32, 7.90, 9.15, 9.63, and 12.27 microns made us suspect contamination from the sample flask. A flask was cleaned as described and flushed with our dry, Coz-free air into the long-path cell and the same unknown bands appeared. The bands are tentatively identified as follows: 3.32 microns, C-H stretch; 7.90 microns, Si-CH8, deformation; 9.15 microns, Si-0 stretch (cyclic tetramer) ; 9.65 microns, Si-0 stretch VOL. 34, NO. 7, JUNE 1962
879
(cyclic trimer) and 12.27 microns, Si(CH& methyl rocking mode (Bellamy, L. J. "The Infrared Spectra of Complex Molecules," pp. 334-9, Wiley, New York, 1960). If the flask were rinsed with benzene-CCL prior to the chromic acid treatment and then cleaned as described, the hands increased in intensity.
This is probably due to increased chromic acid oxidation of the very thin film of silicone grease deposited on the flask walls. To eliminate these infrared hands i t was necessary to remove the stopcock plugs and clean thoroughly the silicone grease from the stopcocks and then fill the flask with chromic acid
cleaning solution and allow it to soak several hours and finally complete the cleaning as described previously. We also find that with Kel-F grease i t is not necessary to remove all the grease from the stopcocks prior to chromic acid cleaning, and in no case " have . extraneous infrared bar . .
Dark-Field Microscopy at Elevated Temperatures on the Kofler Hot Stage Clinton D. Felton.' Stamford Research Laboratories, American Cyanamid Co., Stamford, Conn. HE
most common microscope hot
T stage in use in laboratories is the
Kofler hot stage. Usually the behavior of materials a t elevated temperatures on this hot stage is observed microscopically by bright-field and by polarized, transmitted illumination. Some systems, however, contain certain components which are not visible by such illumination due to transparency, size, isotropy, etc. Frequently these optical discontinuities may readily be made visible by transmitted, dark-field illumination. Yet dark-field is not generally used with the Kofler hot stage simply because it has not been considered or because the difficulties presented by the physical.design of the hot stage seem to preclude its use-Le., its small viewing port, the thickness of the heating block separating condenser and specimen, and the thickness of tkle heating chamber, requiring the use of long working distance objectives. These difficulties were overcome 1-,Y use of the basic central-stop methcId for obtaining dark-field illuminati0n. First, the simple condenser in the h
