The Microanalysis of Gases 11. Carbon Monoxide, Ethylene, and Acetylene FRANCIS E. BLACET,GEORGED. MACDONALD, AND PHILIP A. LEIGHTON Chemistry Departments of Stanford University, Calif., a n d the University of California at Los Angeles, Calif.
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analyses may be in progress a t N AN EARLIER publicaThe method earlier described by the authors f o r one time. A r u b b e r b a n d , tion (1) an apparatus and the microanalysis of gases, using dry reagents, is made by cutting a short length method were described for here extended. The apparatus has been imthe microanalysisof certain gases from a suitable rubber Proved, and Procedures have been devised for the by means of solid r e a g e n t s . prevents the absorbent holder determination of carbon monoxide with silver O X Water vapor was removed by L from extending too far into means of fused phosphorus penthe gas sample. ide, of ethylene with fuming sulfuric acid, and of I n F i g u r e 1, K a n d J are toxide, carbon dioxide by fused acetylene with a mixture of cuprous chloride and potassium hydroxide, and oxyshown aroiected on a v e r t i c a l potassium hydroxide. gen by yellow phosphorus. Hyplane. .Tieir relative positions are s h o w n m o r e c l e a r l y in d r o g e n , carbon monoxide, and methane were determined by means of the above reagents Figure 2, in which the spider supporting the four guides is used in conjunction with an explosion process. The volumes shown properly oriented above the one which supports the gas holders. The gas holders are held in position by steel of samples used were of the order of 0.1 cc. I n the present paper some improvements of the apparatus ribbon springs. The microburet which was first described was ruled arbiare described and new methods of analysis are given for carbon monoxide, ethylene, and acetylene. Results of analysis trarily in millimeter divisions, but is now graduated to read directly in cubic millimeters with the zero mark a t the top of for these gases are included. the scale. One of the major difficulties encountered in this system of IMPROVEMENTS IN APPARATUS AND METHOD microanalysis arises from contamination of the open mercury The number of inquiries which the authors have received in surface. The gas holders and absorbents are put in place regard to this method of analysis has made it seem advisable through this surface and if it is not clean, impurities will get to describe somewhat in detail certain portions of the appa- on the inside walls of the holders and eventually into the capilratus and technic which have been employed. However, i t is lary buret. To eliminate this it has been the authors' pracassumed that the original description (1) is available to the tice to apply suction immediately, through a capillary tube, to this surface whenever any scum or dust particles are disreader. I n Figure 1 are shown two important alterations of the covered. It has been found much more simple to keep the apparatus which was previously described. Formerly, the surface clean by this constant vigilance than to allow it to gas sample and the mercury were moved hp or down the mi- become coated with an appreciable film before cleaning. A croburet by applying pressure to a heavy-walled rubber tube. trap, of course, is placed in the suction line to catch the merAlthough this method of manipulation is simple and can be cury which is drawn up with the impurities. Very little merused with satisfaction by the experienced operator, there is cury will be removed from the reservoir in this way if the always a hysteresis effect in the rubber which causes annoy- above procedure is followed and that which is removed may ance. The device represented by P, R, s,and B in Figure 1 be returned from time to time, after it has been cleaned. A number of clean gas holders (H and J,Figure 1) are ordiwas worked out to overcome this effect. P is an iron cylinder into which the bell-shaped lower end of the buret is cemented narily kept on hand and a new one is used for each analysis. by the sealing wax N , The wax is also used here to close the water jacket of the buret. R represents an elastic rubber cap. SPECIFIC METHODS OF ANALYSIS The lower flange of this cap is firmly secured against the lower CARBON MONOXIDE. Especially prepared dry silver oxide edge of P in a manner which may be deduced from a study of the drawing. S is a metal plunger which is attached by a has been found to be a very satisfactory selective absorbent swivel to the screw B. The space above R is filled with mer- for carbon monoxide. I n the preparation, the oxide is precury. By manipulating B, the plunger is forced either up or cipitated by means of a strong base and thoroughly washed down, causing a flow of mercury or of gas through the capil- by decantation. While still somewhat moist, the solid is comlary buret, A . I n addition to overcoming the hysteresis pressed into pellets by applying a pressure of. approximately effect, this arrangement gives a more positive and delicate 6000 pounds per square inch. These pellets are allowed to control of the volume change in the system than was formerly dry a t room temperature. Since they take up carbon dioxide, obtained. It is designed to be dismantled and reassembled they must not be unduly exposed to the atmosphere. The solid absorbents which have been described hitherto with ease, so that cleaning the buret is not a difficult task. Since P is the only one of the metal parts which comes in con- may be fused into the platinum loop of the holder. This protact with the mercury, it is the only one which must be made cedure cannot be used for silver oxide since it decomposes a t a comparatively low temperature. Hence, to introduce this of some nonamalgamating material. The second improvement in the design of the apparatus con- substance into the gas sample the following expedient is used: sists of placing the absorbent holder guides K directly on the Instead of a loop, a straight platinum wire is employed. The shaft which supports the gas holders H and J . Since in tip of this is moistened with a minute amount of a concenreality there are four absorbent holders symmetrically ar- trated sodium silicate solution and then touched to a piece of ranged around the shaft, this means that several separate the oxide. A regular shaped piece about 1.5 mm. in diameter 272
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INDUSTRIAL AND ENGINEERING CHEMISTRY
July 15, 1933
is to be preferred. Care is taken not to cover more of the surface of the oxide with the cement than is necessary to make it a d h e r e . The cement is allowed to dry for 15 minutes, after which time there is no danger of losing the absorbent when it is being introduced into the gas h o l d e r . Furthermore, the d r y i n g reduces the vapor pressure of the cement to a negligible factor in the analysis. Absorption is u s u a l l y complete in 10 minutes. No volatile products are formed in the reaction, so a follow-up absorbent is not required. Table I gives r e s u l t s of several analyses for carbon monoxidein the presence of dry air, free f r o m c a r b o n dioxide. T h e volume of samples in all tables is given in cubic millimeters. ETHYLENE.T o t h e authors' knowledge,the selective a b s o r p t i o n of the unn saturated hydrocarbons by means of a solid reagent has n e v e r be en quantitatively f s u c c e s s f u l . For reasons which have been given ( I ) , it was not desired to resort to the use of liquid reagents after the p r o c e d u r e outlined by Christiansen (2). These objections have been overcome by using a porous s i n t e r e d glass bead for introducing the liquid reagents. A piece of sintered glass is shaped to a s p h e r e of approximately 2 mm. in diameter. This is attached to a straight platinum wire by heating the wire and FIGURE1. ;DIAGRAMOF APPARATUS FOR MICROGAS letting the end of it become ANALYSIS embedded in the bead. This process does not appreciably diminish the porosity of the bead. The use of this porous bead is illustrated in the following procedure for the absorption of ethylene. TABLEI. RNSULTS OF ANALYSISFOR CARBON MONOXIDE I
27 3
tassium hydroxide bead is added to take up the sulfur trioxide vapor. This absorption is also very rapid. After another 2 minutes the solid may be removed and the decrease in volume of the sample, due to the presence of unsaturated hydrocarbons, is measured. Table I1 gives results of analyses by this method of mixtures of ethylene and butane for ethylene. I n these cases a new sample was prepared for each determination, hence the different theoretical percentages of ethylene. TABLE11. RESULTS OF ANALYSESOF ETHYLENE AND BUTANE MIXTURES DETERMINATION
VOLUME
SAMPLE Cu. mm. 137.53 141.89 132.89 58.88 125.63
ETHYLENE Theoretical Determined DIFFERENCE % % % 50.04 0.00 50.04 +o. 02 51.81 51.83 0.00 50.53 50.53 51.21 -0.06 51.27 50.26 +O.ll 50.15 Average difference +0.04 Average deviation from mean 0.04
'
11
e
DETERMINATION
1 2 3 4
VOLUME SAMPLE Cu. mm. 80.27 72.04 66.09 58.95
CARBON MONOXIDE Theoretical Determined
%
%
DIFFERENCE
%
49.69 49.62 -0.07 - 0 . os 49.68 49.61 -0.12 49.69 49.57 -0.08 49.69 49.16 Average difference -0.09 Average deviation from mean 0.02
In analyzing for ethylene, the bead is dipped slowly into fuming sulfuric acid. The space in the bead becomes filled with the liquid and the air is forced out. The bead is wiped with a piece of filter paper to remove the excess acid from the exterior surface and then introduced in the usual way into the gas sample. Almost instantaneous absorption occurs. After 2 minutes the acid is removed and a slightly moist po-
ACETYLENE.I n order to remove a from mixtures with hydrocarbons of th series, an attempt was made to use a si with an ammoniacal solution of cuprou this with moist phosphorus pentoxide to remove the a m m o n i a . A b s o r p t i o n ,$ ( l occurred, but sufficient reagent could not be introduced in a single bead to remove all of the acetylene present in t h e average sample. H o w e v e r , the principal disadvantage of the method was t h e collection of a voluminous precipitate of copper acetylide on the exterior of the bead, which contaminated the mercury surface as the bead was being removed. Solid c u p r o u s chloride, when moistened, will absorb some acetylene, but the reaction does not go to completion unless a base is used in conjunction with the chloride in order to remove the hydrogen chloride produced. It was found this principle can be used in the following manner fo analysis for acetylene, without the objections arising from the use of a solution. A stiff paste is made by moistening cuprous chloride with a dilute potassium hydroxide solution. This is molded in the platinum loop of an absorbent holder and heated gently until dry, care being taken not to heat the solid until it turns dark in color. This bead gives complete absorption of the acetylene contained in the average sample in less than 5 minutes. The copper acetylide formed in the reaction becomes an integral part of the solid bead and does not contaminate the mercury as it is being removed from the reaction system. The potassium hydroxide takes up all of the hydrogen chloride or water vapor formed in the process, so that the decrease in volume gives directly the amount of acetylene which is present. Mixtures of acetylene with butane and with ethylene have been analyzed by this method with the success shown in Tables I11 and IV. I
TABLE111. RESULTS OF ANALYSESOF ACETYLENEAND BUTANIO MIXTURES DETERMINATION
VOLUME SAMPLE Cu. mm. 137.53 137.42 136.92 136.89 136.97
ACETYLENE
Theoretical Determined DIFFERENCE % % % 45 .io 45.00 -0.20 45.33 45.33 0.00 45.13 45.03 -0.10 45.14 45.18 +0.04 45.14 45.10 -0.04 Average difference -0.08 Average deviation from mean 0.06
ANALYTICAL EDITION
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TABLEIV. RESULTS OF ANALYSESOF ACETYLENE AND ETHYLENE MIXTURES DETERMINATION
VOLUME SAMPLE Cu. mm.
ACETYLENE Theoretical Determined
%
%
DIFFERENCE
%
DISCUSSION O F RESULTS The use of silver oxide as an absorbent was suggested by the work of Lamb and his associates (4, 6, 6) on the catalytic oxidation of carbon monoxide by the hopcalites. I n the microanalysis of gases, where the expense of r e a g e n t s is a negligible factor, silver oxide is superior to the hopcalites not only because it reacts more rapidly, but also because any carbon dioxide which may be produced is immediately absorbed by more silver oxide. According to Gautier (S), the reaction for the absorption of carbon monoxide may be represented as: 2Ag20
+ CO
2Ag
+ A&Oa
The authors’ experience substantiates this, since free silver is produced in the process and no carbon dioftide is liberated. The decrease in volume represents the volume of carbon monoxide present in the sample. The presence of hydrogen introduces an appreciable error in the determination of carbon monoxide b y t h i s method. However, the rate of absorption of hydrogen by dry silver oxide is so slow compared to the rate of carbon monoxide a b s o r p t i o n that the method can be used in many cases, providing the time of exposure is properly regulated. In a series of experiments (Y) it was found that in an average analysis of a sample containing equal FIGURE 3. MICRO- quantities of carbon m o n o x i d e a n d GAS ANALYSIS APhydrogen an error of approximately PARATUS 1.25 per cent in the carbon monoxide Complete except mermay be expected. The magnitude cury and absorbent holders. of this error d e p e n d s (a) upon the physical state of the silver oxide, (b) upon the amount of hydrogen and nonreacting gases present, and (c) upon the time of exposure. It is important that the silver oxide be dry in order to miuimize the hydrogen oxidation. For the purpose for which it was developed, the authors have found this method of separation of these two gases to be Satisfactory. However, in the hope of making further improvements the problem is being given additional consideration. The method given here for the analysis of ethylene is generally applicable to the analysis of unsaturated hydrocarbons in the presence of hydrogen, the methane series, and the other more inert gases. In cases in which fuming sulfuric acid is not needed for the absorption, the treatment with potassium hydroxide is omitted. Since the acid remains in the bead and does not contaminate the mercury surface in the gas holder, there is no danger of getting the reagent and impurities in the buret. The very small amount of liquid reagent used
Vol. 5, No. 4
reduces to a minimum the possible errors due to the dissolving of the remaining gases. The sintered glass may be made in any laboratory by taking ground glass of the proper mesh and heating it carefully until the pieces just begin to fuse. This use of a sintered bead opens up the possibility of using any of the liquid reagents of macroanalysis for the microanalysis of gases. At the same time it eliminates the usual objections to liquids. However, experimental difficulties, such as those encountered in analyzing for acetylene with an ammoniacal cuprous chloride solution, may prevent the use of certain solutions. Most water solutions used in this way would require a follow-up bead to take out water vapor, for it has been found (1) that the normal vapor pressure of water cannot be assumed to exist in these reacting systems. It is felt that the results given in the accompanying tables are typical of those which may be expected from the methods which are given. I n following the course of certain photochemical reactions, over two hundred determinations of carbon monoxide by the silver oxide method have been made in the authors’ laboratories with most satisfactory results.
LITERATURE CITED (1) Blacet and Leighton, IND. ENG.CHEM.,Anal. Ed., 3, 266 (1931). (2) Christiansen, J. Am. Chem. SOC.,47, 109 (1925); 2. anal. Chem., 80, 435 (1930). (3) Gautier, Compl. rend., 126, 871 (1898). (4) Lamb, Bray, and Frazer, J. IND. ENG.CHEM.,12, 213 (1920). (5) Lamb, Scalione, and Edgar, J. Am. Chem. Soc., 44, 738 (1922). (6) Lamb and Vail, Ibid., 47, 123 (1925). (7) Leighton and Blacet, Ibid., 54, 3165 (1932). REOEIVED March 6, 1933. Presented before the Division of Physical and Inorganic Chemistry at the 84th Meeting of the American Chemical Society, Denver, Colo., August 22 to 26, 1932.
Chain Arrangement for Rubber Stoppers R. A. OSBORNAND A. G. STERLING Bureau of Chemistry and Soils, U. S. Department of Agriculture, Washington, D. C. .
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LASS stoppers are easily attached to the necks of their containers by means of a cord or chain. This practice prevents loss, exchange, or contamination of the stopper. NO satisfactory means of fastening a rubber stopper to a container (for alkali or other solutions) has come to the authors’ attention. A method for doing this follows: Place a stopper (of any suitable size) in a lathe and drill through the top end into the center with a 0.06-inch (0.16-om.) centering drill, followed by a 0.187-inch (0.48-cm.) drill. Insert a 0.187-inch recessing tool to the center of the stopper, where a hole 0.125 inch (0.32 em.) wide and 0.31 inch (0.8 cm.) in diameter is made. Select a piece of brass rod of 0.31-inch (0.8-cm.) diameter and of suitable length and machine to the size and shape of the hole in the stopper. Round off the lower edges of this plug, drill a 0.06-inch (0.16-cm.) hole in the upper end of the shaft for the purpose of attaching a chain, and insert in the stopper using glycerol, rubber cement, or water as a lubricant. The time required for the complete operation is less than 5 minutes. RECEIVED April 22, 1933.
