ANALYTICAL EDITION
274
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. .
G
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.
