A New Type of Electrolytic Cell GEORGEI. WHITLATCH AND ROBERT D. BLUE,Indiana University, Bloomington, Ind.
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ORCELAIN cells are used extensively as diaphragms in electrochemical processes, both organic and inorganic, and the conventional, round, white cell is a familiar sight to all workers in this field of chemistry. Commercial cells used for some types of electrochemical work are unsatisfactory, however, in that they do not seem sufficiently porous. Further, difficulty is experienced in that the commercial cells, after 36 to 100 hours of service, begin to disintegrate, and pieces of the outer surface of the cell “spa11 off” into the electrolytic bath. The purpose of this paper is to describe a new type of electrolytic cell devised for inorganic electrochemistry. The length of service derived from this new type of cell is in striking contrast to the service obtained from the commercial round cell. One of these new cells has been in use for over a year and as yet has shown no serious deterioration. The porosity of the cell is also considerably greater than that of the usual commercial cell.
OF MULTIPLE-CELL Box FIGURE 1. DIAGRAM
Although it is possible to make the ordinary round type of commercial cell by the casting process, the writers found it more convenient to make thin plate-like diaphragms which were used as partition diaphragms between the cells of a multiple electrolytic cell box. The multiple-cell box in which the diaphragms were used was of stoneware, consisting of three cells, made especially for the diaphragms.
THE DIAPHRAGMS The mixture used in casting the diaphragms, expressed in parts by weight, was as follows: French flint... , . . . . . , . . . . . , . , 1 part Kentucky ball clay., . . , . . . . . . . 2 parts English china clay . . , . . . . . . . . . 2 parts The three ingredients were first sifted through a 100-mesh screen and then mixed with a sufficient quantity of water to produce a slip of fairly low viscosity. This clay-flint-water mixture is generally known as a “casting slip.” l n preparation for the casting of the diaphragms, a shallow tray with sides a t least 1.5 inches (3.81 cm.) in height and a plaster of Paris floor 1 inch (2.54 em.) in thickness was constructed. The tray measured approximately 1 foot (.304 meter) square. The casting slip was poured into this tray until it covered the plaster floor to a depth of about 0.16 inch (0.42 cm.). A slight jarring of the tray during the pouring of the mixture spread the slip uniformly over the floor of the tray. The plaster floor of the tray absorbed the excess water from the slip rather rapidly, and in less than an hour the casting had “set,” although it was still moist and comparatively soft. At this stage the casting was divided into 3-inch
(7.62-cm.) squares with the aid of a spatula. The squares were then allowed to dry thoroughly in air.
THHMULTIPLE-CELL Box The stoneware multiple-cell box and the method of fitting the diaphragms into it are shown in Figure 1. The cell box was approximately 5 by 2.5 hy 2.25 inches (12.7 by 6.35 by 5.71 cm.) outside dimensions, and was built by hand from an Indiana underclay (fire clay) having a refractoriness of Cone 10 (standard pyrometric cone scale). The box was glazed with Albany slip glaze. (The Albany slip glaze is a standard product and can be secured from any firm dealing in ceramic supplies.) I n the construction of the stoneware box, a wooden boxmold slightly larger than the desired cell box was used. The underclay, after being ground and screened, was mixed with water to a fairly stiff plasticity, rolled into a sheet approximately 0.25 inch (0.63 cm.) in thickness, and then cut into strips 2.75 inches (6.98 cm.) in width and 5.5 inches (13.97 cm.) in length. One of these strips was placed on the floor and one along each of the inside walls of the wooden mold. The edges of the strips were slightly moistened and, by pressure of the fingers, were easily “welded” together a t the corners and along the floor seams. All joints inside the box were further welded and smoothed over with a spatula. The box could now safely be slipped out of the mold, and all exterior joints and seams were welded and smoothed over. The cell box was allowed to air-dry for an hour or two, but while still appreciably moist, two grooves, about 0.16 inch (0.42 cm.) wide and 0.13 inch (0.31 em.) deep, were cut in each side and across the floor of the box. The grooves form slots for holding the diaphragms in position. After cutting the grooves, the cell box was completely air-dried and then further dried for 8 hours in a desiccator heated to 100” C. , FINISHINQ CELLBox On removal of the cell box from the desiccator, the diaphragms were trimmed to fit the prepared slots in the cell box and were slid into position. Care was exercised to see that the diaphragms fit snugly into the slots. With the diaphragm in place, the entire cell box was dipped into a thin slip of Albany glaze. The glaze was allowed to air-dry before the cell box was again sent to the desiccator where it was given a second drying of 4 hours a t 100” C. On removal from the desiccator this second time, the raw glaze was thoroughly scraped off the diaphragms to within 0.25 inch (0.63 cm.) of their margins. The cell box was fired in a muffle kiln until the glaze “matured.” The type of glaze used on the cell box matures about Cone 4, and experimentation has demonstrated that this temperature is sufficient to produce the desired porosity of the diaphragms as well as burn the body of the cell box to a well-fused condition. The porosity produced a t this heat in a diaphragm composed of the mixture used by the writers is considerably higher than the porosity of the commercial cell and has proved satisfactory for the type of research for which the diaphragms have been used. CONCLUSIONS The cell-box described above has several points of merit. I n the first place, the multiple-cell feature of the box is
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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.
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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
