I N D U S T R I A L A,VD ENGINEERING CHEMISTRY
January, 1928
for, as previously mentioned, a heavier coating of tin reduces corrosion in the can as measured by its tendency to perforate. Increasing the tin coating decreases the area of the cathodic iron relative to the anodic tin and, in accordance with the electrochemical theory, corrosion of the iron is reduced. Again, commercial experience shows that enameled cans perforate sooner than plain cans. The enamel covers a larger area of tin than of iron, thus reducing the area of the
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tin relative to that of the‘ iron. This follows from the fact that at points where relatively more iron is exposed owing to forming and closing of the can the enamel is also least continuous. On the basis of the electrochemical theory, corrosion of the anode should increase as the relative area of the cathode increases. The mechanism of corrosion as indicated by these results is in harmony with the corrosion encountered in commercial experience.
An Inexpensive Cell for the Purification of Colloids b y Electrodialysis’ Richard Bradfield DEPARTMENT OF‘ SOILS, UNIVERSITY on MISSOURI, COLUMBIA, Mo.
PIIOPI’Gthe greatest impediments to progress in colloidal chemistry have been the difficultiesinvolved in obtaining pure, reproducible products. Nearly all colloids, synthetic or natural, contain variable quantities of ordinary electrolytes which are either neglected or only partially removed by ordinary dialysis. The purification of colloidal electrolytes in which one ion is of colloidal, the other of crystalloidal, dimensions is even more difficult to accomplish, but no less important for an understanding of the behavior of the sol. The classical dialysis of Thomas Graham is extremely slow and tedious. It has long been knoryn that the rate of purification could be greatly acce1er:tted by the application of an electrical current to electrodes placed outside the dialyzing membrane containing i,he colloid. But not until recently has this method of purification, now commonly termed “electrodialysis,” received the attention it seems to deserve. Freundlich2has found that in the case of serum a degree of purification that would require a week by ordinary dialysis ELECTRO-DIALYSIS CPLi can be accomplished in 10 to 40 minutes by electrodialysis. Dhkr6,3 Paull,4 Bechold,b and numerous others have also called attention to the advantages and limitations of the process, In spite of this increased interest in the subject, so far as the authorisaware, there is no apparatus on the American market for t h i s p u r p o s e . For that reason a description is glr-en herein of simple, inexa I pensire cell which can
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1
Received August 20,
1927. 2 B o g u e , “Colloidal B e h a v i o r , ” P 300, McGraw-Hill Book c0 1924. * Kollor6-2, 41, 243
Top V/ru
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Alexander, “Colloid
Chemistry,” p, 834, ChemF~~~~~ I--Rubber Cell Made from s~~~~~~ B a t t e r y Case
ical Catalog C o , 1926
be easily made from an old rubber storage battery case, Cells of this type have been used in the author’s laboratory for three years and are still giving satisfaction. Description of Cell
The construction of the cell is shown in Figure 1. The battery jar is sawed into three sections, the outside sections about the width desired in the finished cell. The width of the resulting center section will vary with the type of cell used, but it can be sawed again into any desired size. The following dimensions have been found to be satisfactory for routine work: width of each section, 4.0 c m , depth. 14 t o 15 cm., length, 14 to 15 cm. Such a cell will have a working capacity of about 700 CC. in each compartment. The edges of each section are carefully smoothed and squared so that watertight joints may be obtained without the use of gaskets. The three sections of the cell are held together by seven brass rods, three of which are regularly spaced on each side of the cell, and one in the middle of the cell bottom. These rods pass through holes drilled in the cell itself, as shown by the dotted 100 lines i n F i g u r e 1. T h i s a r r ~ ~ g e m e n0t holds the membranes ?*’ t%htly in Place and Q P r e v e n t s warping of E 6 0 the different sections e of t h e cell. Brass C40 strips about 2 wide and t h e s a m e length as the cell, with 0 holes drilled to corre- a spond with those in the cell Proper, serve as WdU3-s and hold Figure 2-Rate of Electrodialysis of Dife r e n t Ions w h e n Placed b e t w e e n Parcheach rod in place. If fment Membranes the edges Of the cell har-e been properly squared, water-tight junctions can be obtained by merely tightening the thumb screws on each rod. Any type of dialyzing membrane can be used. A good grade of parchment paper is satisfactory for most purposes. The cathode may be made of nickel or copper gauze, the
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can be used for continuous electrodialysis by a continuous stream of distilled water to enter a t the bottom
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INDUSTRIAL AND ENGIXEERING C H E X I S T R Y
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and flow out through an exit tube a t the top, or it may be drained periodically and fresh distilled water added. The most suitable voltage to apply a t the electrodes will vary with the nature of the sol being electrodialyzed, and with its content of electrolyte. It is generally best t o keep the current under one ampere in order to avoid too much heating. This can be done by controlling the line voltage or, more conveniently, by using an adjustable rheostat connected in series with the cell. A line voltage of 100 to 220 volts is commonly used. Rate of Electrodialysis The comparative rate of electrodialysis of different ions through parchment membranes is shown in Figure 2. Tencubic centimeter samples of solutions of KC1, KzSO?, and KH2P04,all normal in potassium content, vere placed
Vol. 20, No. 1
in 500 cc. of water in the middle chamber of the electrodialysis cell and 100 volts d. c. applied a t the electrodes. The anolyte and catholyte were siphoned off every 10 minutes and titrated with standard acid or base. I n every case the cation is removed much more quickly than the anion. The rate of removal of the cation is influenced by the nature of the anion with which it is combined, while the rate of removal of the anions is in the order C1>SO4>HzPO4. I n every case the cation is removed quantitatively within 20 to 40 minutes. The anion can also be removed quantitatively, but the time required is greater, especially in the case of the phosphate ion. The rate of removal of anions should be facilitated by the substitution of a positive membrane for the negative parchment membrane on the anode side. L4 satisfactory positive membrane has not yet been found, although the chromated gelatin membrane2 has proved helpful in certain cases.
Present Status of Coal By-Product Nitrogen' Mildred S. Sherman FIXEDNITROGENRESEARCH LABORATORY, BUREAU OF CHEMISTRY A N D SOILS, WASHINGTON, D. C.
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ITHIN the last fifteen years coal has been a T-ery influential factor in wresting the world nitrogen monopoly from Chilean nitrate. Power for the manufacture of fertilizers is obtained from coal; 85 to 90 per cent of the hydrogen required for the synthetic fixation of nitrogen will be produced in 1927 through coal, either from water gas or by-product coke-oven gas; and Aikman, Ltd. (London), estimates that of the world consumption of 1,315,000 tons of nitrogen in the year ending June 30, 1927, 24 per cent, or 310,000 tons, were produced as a distillation product of coal. This figure of 310,000 tons of nitrogen from by-product ammonium sulfate shows an increase over the figures of 300,000 and 275,000 tons for the two previous years and on the basis of 850.40 per ton (2000 pounds), the average price of ammonium sulfate for that period, was worth $73,745,280. While there have been no startling new developments in the processes for treating coal by-products within the last year, the industry has made steady progress and developed its operating technic along lines already established. However, three decided tendencies have become apparent. Rigger and more efficient ovens are being built. The trend of the industry is for larger unit coke-oven capacity. I n America the average oven holds a charge of 12 tons of coal. There is an increasing number of plants having 16-ton ovens and the Carnegie Steel Company a t Clairton, Pa., is now constructing three hundred and forty-eight ovens of the Koppers-Becker type, whose individual capacities will be 19.13 tons of coal per charge. It is estimated that this new group of ovens will produce 2,721,000 tons of coke annually, so that this new plant alone will potentially be able t o recover 45,000 tons of ammonium sulfate per year. The city gas companies are becoming more closely allied to the by-product coke-oven interests. I n the United States five of the eleven companies which placed new by-product coke ovens in operation in 1926 were connected with public utilities companies and will market their surplus gas through these systems. City gas works thus owned 27 per cent of the new ovens opened up in the past year, and these ovens will manufacture 22 per cent of the additional estimated annual coke output. Furthermore, the keen competition due to the increased 1
Received October 13,1927.
production of synthetic nitrogen is forcing the by-product companies to convert their ammonia liquor to sulfate. &lore and more industries needing highly pure ammonia are looking to the synthetic plants t o supply their wants and the output of the coal industries will be converted. into fertilizer materials. A study of the statistics2 for the United States for the year ending June 30, 1927, will give an accurate picture of the condition of the industry. On that date there were seventy-seven active by-product coke-oven plants and one idle one, and these plants were producing slightly more than 82 per cent of their capacity. These plants had about 12,000 ovens in actual use. During the year eleven companies placed 679 new ovens in ~ p e r a t i o n from , ~ whose estimated annual production of 3,794,470 tons of coke it will be possible, using present methods, to recover 12,920 tons of nitrogen. On December 31, 1926, fourteen companies were constructing 945 new ovens, whose annual coke production capacity will be 6,304,250tons of coke with the corresponding recovery of 21,450 tons of nitrogen. Table I s h o w there has been a steady increase in the nitrogen produced from by-product coke ovens in the United States in the last three years. I n addition to these figures, the gas works have recovered, as the three-year average, 5300 tons of nitrogen per year. Table I-Kitrogen Recovered f r o m By-Product Coke Ovens COALCONAMMOXIUM YEARENDING SUMED IN BYSULFATE hTITROGEN JUNE30 PRODUCT OVENS EQUIVALENT EQUIVALENT Tons Tons Tons 595,050 126,150 1925 51,525,000 700,774 148,564 1926 60,653,000 738,772 156,620 1927 63,963,000
During the calendar year 1926 the nitrogen needs of the United States were such that it was necessary to import 155,200 tons of nitrogen in the form of Chilean nitrate valued a t $42,781,400. Additional 22,880 tons of nitrogen mere imported in the form of other salts, showing that our consumption was 178,080 tons greater than our domestic production. Although our synthetic-nitrogen plants will probably produce a t least 23,000 tons of nitrogen in 1927, 2
Taken from Weekly Coal Reports of U. S. Bureau of Mines. Steel Plant, 16, 41 (1927).
* Blast Fuvnace
