Microanalvsis of Gases J
A Combined Toepler Pump and McLeod Gage Designed for Microanalysis with Dry Reagents W. L. HADEN, JR.', AND E. S . LUTTROPP2 University of North Carolina, Chapel Hill, N. C.
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X CONNECTION with some work on the photolysis of gaseous ('), a new method was desired for measurement and analysis of gas samples Of the Order Of to 500 cu. mm. (at atmospheric pressure). While no exhaustive tests have been made as to the accuracy or versatility of the apparatus, since accuracy better than about 1 per cent was not required, the method seems Of SUffiCientinterest to Warrant publication. Difficulty had been experienced in using a horizontal microburet, in the dry method of analysis of Blacet, MacDonald, and Leighton ( I ) , Partic'-llarlY with the smaller samples. This difficulty appeared to be due to appreciable quantities of air carried into the sample with the pellet used to absorb components of the gas. order to eliminate this source of error, as well as others Of less importance, the aPparatus shown in Figure 1 was constructed, combining the usual Toepler pump and a n analysis system into one fairly compact unit.
Procedure The apparatus is evacuated through J and N while separated from the reaction system by the mercury cutoff. The stopcocks to the vacuum line are then closed, the mercury cutoff to the reaction system is opened, and the gas to be measured and analyzed diffuses into A and B from the reaction system through tube M . Air admitted through stopcock G causes the mercury in the reservoir to rise, forcing the gas in A up into chamber B , Stopcock C is then closed and the mercury is lowered so that another portion of the gas may fill A and be umped into B.
$:: Thep sample , f p ~ ~ ~ h ~f ~ ~ ~ g:2 ~~ ~, $" o, " z, e ~~~ & ~~ ~ ~ . p u m p 9 is measured by lowering the mercur to point K and allowing the gas in B to fill the large bulb, A . Aosing stopcock c causes all except about 0.4per cent of the sample to be closed off in the large bulb, a loss which may be corrected for if desired. The mercury is then run up to one of the calibration marks, E, F . The pressure of the gas is given by the difference in height between the calibration mark used and the mercury column in H . Knowing the volume from the calibration and the pressure from observation, the quantity of sample is determined. Analysis of the sample is carried out by using a dry absorbing agent such as those em loyed in the method of Blacet, Mac8onald, and Leighton (1). The ground-glass plug, L, is removed from the chamber and a pellet of the absorbing agent-. g., silver oxide for carbon monoxide absorption-is attached to the tip of the plug by picein or in any other convenient manner. The use of severa1 interchangeable plugs, one for each reagent, facilitates this operation. With the plug and reagent inserted in the chamber, air is removed by opening stopcock N to the vacuum line. When evacuation is complete, the sample is again forced into the chamber where absorption takes place. The residue is measured in the same manner as the original sample.
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Apparatus The apparatus, which is of all-glass construction, consists essentially of a double-range McLeod gage of about 500-cc. volume with accurately calibrated volumes of 1 and 0.1 cc. marked at E and F. A chamber, B, of about 1.5 to 2 cc., is connected to the top of the age by an oblique-bore 1.5-mm. capilfary stopcock. This chamber, which holds the sample and reagents, is closed by a ground-glass plug, L, and is connected t o a high-vacuum line by the stopcock, N . The gage section is joined to the mercury reservoir, D , by a mercuryseal ground-glass joint to facilitate dismantling for cleaning. A Dewar seal is used here to reduce the height of the apparatus. As in the usual McLeod gage designed for reading higher pressures, the distance between the mercury surface in the reservoir and the calibrated capillary on the bulb should be as short as possible. The available pressure scale is determined by the distance above the calibration marks, E, F , that atmospheric pressure will force mercury in the scale capillary, H , about 45 cm. in this case. The apparatus is connected a t J to the high-vacuum line through a vacuum stopcock and to the reaction system through a mercury cutoff. (A stopcock may replace the mercury cutoff when stopcock grease is not objectionable.) 1 Present address, Pittsburgh Plate Glass Company, Barberton, Ohio. 8 Present address, Radiation Laboratory, University of California, Berkeley, Calif.
FIGURE 1.
APPAR.4TCS
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I n the analyses for which the apparatus has been used, some difficulty was originally experienced due t o traces of moisture which were retained on the absorbing pellets (potassium hydroxide, silver oxide) during evacuation, but which appeared later when the residue was measured. Since the amount of water vapor was usually sufficient to saturate the small volume to which the gas is compressed during measurement, it was found convenient to permit this saturation to take place and then subtract the water vapor pressure from the observed pressure rather than use an extra pellet for drying the gas. While the present apparatus has been employed only in the analysis
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INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE I. ANALYSESFOR CARBONMONOXIDE (Rollefson and Grahame, 3, found 49 * 0.3%) Sample Residue co Cu. mm. 112.2 327 313 69.8 190.8 479
CPL.mm. 56.6 162.4 159.0 35.0 95.5 245
% 49.6 50.3 49.2 49.9 49.8 48.8
of carbon monoxide, the method should be applicable to any analysis in which liquid reagents may be avoided. A few typical analyses for carbon monoxide are shown in Table I. No attempt has been made to improve the results obtained, but it is believed that increased time of preliminary evacuation and removal of water vapor would lead to improved performance. There are a number of possible designs that may be applied to the reaction chamber to increase the versatility of the apparatus.
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For example, ground joint L could be replaced by a spherical ground joint, its female section being connected t o stopcock C . The male section would have any desired number of indentations on its ground surface, within which could be attached pellets of the same or various reagents. In the first case, this would enable the reagent to be renewed merely by exposing a different indentation to the reaction chamber. In the second case, should the gas contain a number of components, reagents for removing only certain components could be exposed t o the reaction chamber aa desired. It is also possible that an explosion, a combustion, or an oxidation reaction chamber may be designed for the apparatus.
Acknowledgment The authors wish to express appreciation for the advice and encouragement of 0. K. Rice in the design and construction of this apparatus.
Literature Cited (1) Blacet, MacDonald, and Leighton, IND.ENQ.CHEM.,Anal. Ed., 5, 272 (1933). (2) Haden, Rice, and Meibohm, J. Chem.Phys., 8,998 (1940). (3) Rollefson and Grahame, Zbid., 7,775 (1939).
Separation of Calcium Nitrate from Strontium Nitrate By Monobutyl Ether of Ethylene Glycol H. H. BARBER, University of Minnesota, Minneapolis, Minn
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N SEPARATING and identifying barium, calcium, and
strontium after these elements have been precipitated &s carbonates, use is made of the differential solubilities of the salte of the a h l i n e earths or the selective solubilities of organic reagents on the anhydrous chlorides or nitrates of these metals. While the different procedures have given fairly mtisfactory separation of the three alkaline earths, they have not offered a clear-cut and positive separation. The uncertainty has been especially marked with students in analytical chemistry and with the analyst who does not have ocoasion to make frequent separations of the alkaline earth metals. Although the Merentia1 solubilities of the alkaline earth s a l h cannot be changed appreciably by varying the concentration of the separating reagents, the selective solubility of organic reagents on the anhydrous chlorides or nitrates should afford a positive separation if a reagent could be found which had a high solvent action on, say, the nitrate of calcium and a negligible, or exceedingly low, solvent action on the nitrate of strontium. Anhydrous alcohol-ether mixtures (4, isopropyl alcohol (a), amyl alcohol (S),acetone (6),butyl alcohol (6),etc., have afforded a fair separation of the anhydrous chlorides or nitrates of the alkaline earths. However, the ether-alcohol mixture is rather dangerous on account of its easy inflammability. With these organic solvents the anhydrous solvent must be prepared and protected from the moisture of the atmosphere and should be used without moisture contact in order to keep the selective solvent action a t a maximumminimum ratio. Even then, these reagents do not give a complete separation of the anhydrous chlorides or nitrates of the alkaline earths. An investigation of other solvents was undertaken, and the monobutyl ether of ethylene glycol (butyl Cellosolve) was
found to have the desired properties. This reagent gives a complete separation of the anhydrous nitrates of strontium and calcium and, their hydrated nitrates are rendered anhydrous at, or below, the boiling point of the solvent (170.6' C.). Furthermore, the anhydrous solvent is obtained by heating it to the boiling point when dehydrating the calcium and strontium nitrates-that is, the calcium and strontium nitrates and the solvent are rendered anhydrous in one operation. Because of this double action, it is not necessary to dehydrate the nitrates by heating them at uncertain temperatures, and then attempt to dissolve the more soluble nitrate by triturating the baked nitrates in the solvent which is absorbing moisture from the air as well as from the vessel in which the salts were dehydrated.
The Reagent Commercial butyl Cellosolve having a boilin range from 163' to 174' C. was used. About 96 per cent distifs below 172'. It is water-white, somewhat hygroscopic, soluble in water in all proportions, does not have an unpleasant odor, is not easily ignited, but will burn when vaporized into a flame. The pH of the material used was 5.8. The inflammability does not appear to be dangerous or explosive, when the soivent is used as directed. The vaporized Cellosolve should be ignited when it is boiled off.
Semimicroprocedure for Analysis of Alkaline Earth Group The alkaline earth group will be contained in the filtrate from the previous group precipitation. This filtrate will be ammoniacal and will contain ammonium sulfide. Add 1 drop of neutral red indicator (pH 6.8 to 8.0) and boil the solution until it turns from yellow t o red and becomes clear. [On boiling, the decomposition of the ammonium sulfide results in a deposit of sulfur (white), but when the solution becomes distinctly red, the white deposit disappears, and the solution becomes clear.] Make the volume of the filtrate t o about 2 ml. by
