July 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
desirable as it gives a very compact unit containing two cells for the electrodes and a central supply cell. Further, the stoneware box and its cells are glazed with a material that is resistant to most acids and bases, and therefore is welladapted to chemical work. The diaphragms are sealed into place by the glaze and danger of leakage around them is impossible as long as the glaze remains intact. Sealing of the diaphragms into position by the glaze also allows the use of the cell box for heated and strongly alkaline solutions; this would not be possible if a wax seal were used. The composition of the mixture used in the diaphragms is similar to that used in the manufacture of commercial cells.
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The writers do not claim any originality for that feature, but the casting method of making these diaphragms is felt to be an improvement over the commercial cell made by dry-press methods. Casting of the diaphragms has resulted in a more uniformly porous product free of spalling, and it is believed that this method of making diaphragms has a practical value. It is entirely possible to make the electrolytic cells in the usual round shape by casting methods, and the writers are of the opinion that the present commercial cell can be improved by manufacturing such cells by the casting process instead of by the present dry-press methods. RECEIVED March 21, 1932.
Capacity of Drying Agents for Gas Masks M. BLUMER,C. J. ENGELDER, AND A. SILVERMAN, University of Pittsburgh, Pittsburgh, Pa.
D
RYIKG agents for the removal of water vapor from gases are generally employed on the basis of their aqueous tension, and as a rule the investigator assumes the use of unlimited amounts depending merely on the drying ability rather than the drying capacity. When specifications limit the space which may be occupied by a drying a.gent, as is the case in gas-mask canisters, the problem becomes quite different. Here it is necessary not only to know the aqueous tension of the dryer, but also its life, or in other words, its capacity, in the limited space which it occupies. Were one able to depend on theoretical values for the water which can be taken up by anhydrous substances to form definite hydrates, he might be inclined to think that the life of the dryer could be extended to this limit. Where data are available on the aqueous tension of hydrates, the amount of moisture which can escape is known. Certain substances such as calcium chloride and phosphorus pentoxide will, as we know, continue to absorb water beyond the point where definite hydrates have formed. Here we are not only confronted with a tendency toward increasing aqueous tension, but also with the further tendency of the dryer to become pasty or even liquid. For units such as the canisters in gas masks, pasty and liquid dryers cannot be used. I n the investigation undertaken, a catalyst for the conversion of carbon monoxide to carbon dioxide was employed at room temperature, with the gas stream a t 50 per cent humidity, and with a rapid flow of gas. The use of various adsorbents, reactants, and dryers necessarily limits the space which the drying agent may occupy in a unit which shall be of a convenient size for safety and rescue work. With this in mind, the life of the drying agent was based on its ability to insure complete conversion of the carbon monoxide to carbon dioxide, with the particular catalyst concerned, in low-temperature conversion. A catalyst sufficiently active to oxidize completely the carbon monoxide present in the gas a t temperatures as low as 0" C. was found to be very sensitive to water vapor. The activity of this catalyst was decreased by 5 per cent when 1 per cent of its weight of water was adsorbed, and it became completely inactive when it had adsorbed 2.5 per cent of its weight of water. The above characteristics of the catalyst suggested its use for the determination of the capacity of drying agents. The catalyst was intended for use in a carbon monoxide
gas-mask canister whose volume is limited by practical considerations, such as weight and breathing resistance. The space occupied by the drying agent was 150 cc. One tenth of this volume was used in the following tests. A drying agent had to satisfy two requirements before its capacity was determined: it has to be granular in form in order to have low resistance to gas flow; also no noxious gases should be eliminated when water was adsorbed. As has been intimated, the above requirements eliminate all liquid drying agents commonly used, as sulfuric or phosphoric acids, as well as materials which react with water with the subsequent evolution of a gas or vapor-i. e., a calcium carbide. Phosphorus pentoxide cannot be used, as it has a high initial resistance to gas flow which rapidly increases with the absorption of water vapor. METHODOF TESTING The method used in testing the capacity of the drying agents was as follows: 15 cc. of the drying agent of 12-14 mesh were placed in an upright glass tube, 3 em. in diameter, and the catalyst placed above it, a wire screen disk separating the two materials. Air 50 per cent saturated with water vapor a t 20" C., containing 1 per cent of carbon monoxide by volume, was passed through the tube at 200 liters per hour. A carbon monoxide indicator sensitive to 0.01 per cent of carbon monoxide was used to determine the presence of carbon monoxide in the effluent gas. Twenty cubic centimeters of catalyst granules of 12-14 mesh were used in all tests. The capacity of the drying agent was measured by the time required to decrease the activity of the catalyst from 100 to 95 per cent. This 5 per cent decrease in activity meant that the dryer had permitted 0.17 gram of water vapor, which is 1 per cent of the catalyst weight, to escape and be adsorbed by the catalyst. The relative humidity of the gas WAS controlled by passing it through two bottles of dilute sulfuric acid placed in series, the vapor pressure of water vapor over the acid being 13.2 mm. of mercury a t 20" C. At 200 liters per hour, the barometric pressure being 746.0 mm. of mercury, the volume of water vapor in the gas is 3.54 liters per hour, which is equivalent to 3.2 liters per hour a t standard conditions, or 0.043 gram of water per minute. Since 4 minutes are required to deliver 0.17 gram of water, the
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ANALYTICAL EDITION
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time when the dryer failed, as determined by experimentation, was reduced by 4 minutes, thus giving the actual life of the drying agent. All drying agents tested were dehydrated at 400" C. under a total pressure of 20 mm. of mercury, with the exception of aluminum oxide and magnesium perchlorate. Aluminum oxide was dehydrated by heating to 1000" C. for 6 hours, magnesium perchlorate by gradually heating to 200" C. under a total pressure of 5 mm. of mercury. TABLEI. CAPACITY OF DRYING AQENTS WT.OF WT. OF MATEW A T ~ R RIAL OCCUPY- WATER ABSORBED ING 15 cc. ABSORBED Minutes Grams Gams % 71 3.04 11.2 27.2 ALOE 56 2.40 7.5 32.0 Mg C10d1 56 2.40 11.0 21.8 ca&a 25 1.11 30.0 3.7 BaO CaCh,sodalime (50% each) 20 0.86 9.5 9.05 I6 0.69 27.0 2.6 BaOi Ala SO4)a 13 0.56 7.4 7.6 6 0.258 15.2 1.7 NabH pellets 4 0.172 11.6 1.5 NazSOi 2 0.086 7.8 1.1 MgCla 1 0.043 8 . 3 0.52 MgSOr crto 1 0.043 21.2 0.21 DRYING AGENT
LIFE
COMPARATIVE CAPACITIES OF VARIOUS DRYINGAGENTS Of the twelve drying agents tested in the above manner, only three were able to protect the catalyst for a minimum of 1hour. Some of the drying agents permitted a small amount
of water vapor to escape from the start, the amount increasing as the material became hydrated. Calcium chloride, calcium oxide, and sodium hydroxide belong to this class. Others completely absorbed the water vapor up to a certain point, and then broke sharply, causing a rapid decrease in the activity of the catalyst. Magnesium perchlorate, aluminum oxide, sodium sulfate, barium oxide, and barium peroxide belong to this group. Table I contains the experimental data, 15 cc. of drying agent and 20 cc. of catalyst being used in each test. The significant value in this table is the weight of water absorbed by a definite volume of drying agent. Aluminum oxide absorbed the most water; next were calcium chloride and magnesium perchlorate. The others had relatively poor capacity. It is of interest to observe that calcium chloride and magnesium perchlorate have the same capacity for water, although calcium chloride has a higher vapor pressure than magnesium perchlorate. The important difference in their behavior is that calcium chloride permits a small but measurable amount of water vapor to escape from the start, whereas magnesium perchlorate completely dries the gas until its capacity is reached. R ~ C E I V EMarch D 4, 1932. Presented before the Division of Gsa and Fue Chemistry at the 83rd Meeting of the American Chemical Society, New Orleans, L a , March 28 to April 1, 1932. Contribution 229 from the Department of Chemistry, University of Pittsburgh.
Direct Gravimetric Determination of Sodium in Commercial Aluminum EARLER. CALEY,Frick Chemical Laboratory, Princeton University, Princeton, N. J. HE magnesium uranyl acetate method for sodium is
T
capable of giving satisfactory quantitative results when minute quantities of the element are present ( I ) , and aluminum does not interfere with the determination (3). Since sodium is sometimes present as an impurity in aluminum, it was thought desirable to ascertain whether or not this method could be applied directly for estimating the percentage of this impurity in the commercial metal, and thus avoid difficulties inherent in any method based upon the preliminary separation of the sodium from the aluminum and other components of this material. The samples for the experiments were furnished through the courtesy of the Research Laboratories of the Aluminum Company of America. As the result of certain preliminary trials, the procedure followed was first to dissolve the weighed sample of drillings in the minimum possible amount of dilute hydrochloric acid, using a silica dish for this purpose. After dilution with water, the solution was filtered and the filtrate was concentrated to the smallest possible volume in a Pyrex flask, usually until hydrated aluminum chloride just started to separate. Then 100 cc. of magnesium uranyl acetate reagent were added and the determination completed as detailed elsewhere (2, 3). Apparently the various other impurities in the particular samples examined caused no interference. Precipitates were examined for silica with a view to applying a correction, but the amount present was always found to be insignificant. There was no reason to suspect that metallic impurities would cause error, and no evidence was found that they did. With a sample of comparatively high sodium content the method proved quite satisfactory, As the results in Table I
show, the individual determinations checked well with each other and with the value for the sodium content of this particular material as determined in the laboratories of the Aluminum Company of America by their procedures. With a sample of somewhat lower sodium content, however, considerable difficulty was experienced in reducing the solution volume of the necessarily larger sample down to the point required for obtaining correct values by this method. The irregular results obtained in the second group of determinations reflect this difficulty. Even the use of a more concentrated reagent and the addition of this to larger volumes of solution, in this case 10 to 12 cc., as recommended in a recent paper ( I ) , failed to produce entirely acceptable results. The last three vaIues in the table were obtained in this manner.
DETERMINATION OF SODIUM IN COMMERCIAL TABLEI. DIRECT ALUMINUM WT.OF SAYPL~ SAMPLE TAKEN Urams A 0.750 1.000 1.500
B
B
2.000 2.000 2.000 2,000 2.000 2.000 2.000 2.000
2.000
WT.OF SODIUM FOUND PPT. To3rd To,2nd FOUND decimal decimal Gram % % 0.04 0.0183 . 0.037 0.035 0.04 0.0230 0.037 0.04 0.0357 Av. 0.036 0.04 0.0114 0.009 0.01 0.016 0.02 0.0204 0.013 0.01 0.0171 0.014 0.01 0,0185 0.007 0.01 0,0095 0.015 0.02 0,0190 Av. 0.012 0.01 0.009 0.01 0.0115 0.008 0.01 0.0107 0.013 0.01 0.0173 Av. 0.010 0.01
STATED VALU~
% 0.04
0.009
0.000
