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to find the bicarbonate normality a t which the capacity of the whole cycle (absorption and boil-off) will be maximum. The absorption rate coefficient, KG,and the mean driving force, AP,,., for the absorption of carbon dioxide in sodium carbonate-bicarbonate solutions, vary with temperature and with bicarbonate normality in such a way that, for any apparatus which is to perform a given absorption task, there is a particular combination of temperature and range of bicarbonate normalities which will permit maximum capacity. The information furnished by the experimental work described in this paper should help one to select the optimum conditions of temperature and bicarbonate normality for an apparatus which is to operate mithin the range of conditions considered in this paper. In considering absorption where the liquor composition (bicarbnate normality) changes throughout the apparatus, a logarithmic mean driving force, such as used for the work described here, may sometimes lead to serious error. It may be demonstrated (6) that the logarithmic mean is justified when (as in the experiments of the research described here) the apparatus is so short or the volume of liquor used so large that liquor composition changes only slightly throughout the apparatus, and, consequently, the equilibrium pressure of carbon dioxide exerted by the liquor is essentially constant. When the equilibrium pressure of carbon dioxide exerted by the liquor changes throughout the apparatus, the use of the logarithmic mean driving force is justified only if the equilibrium pressure is directly proportional to the amount of carbon dioxide which has been absorbed by the liquor (Henry’s law). For the absorption of carbon dioxide in carbonate-bicarbonate solutions Henry’s law does not hold, and use of a logarithmic mean mill yield a result which may be more or less in error. When the change
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(throughout the apparatus) in the equilibrium pressure of carbon dioxide exerted by the liquor is small compared to the least value of AP in the apparatus, use of the logarithmic mean will yield results which are sufficiently accurate for most engineering purposes; when the change in equilibrium pressure is appreciable (of the same order of magnitude or greater) compared to the least value of AP, use of the logarithmic mean may introduce an error -which is too large to be tolerated. Whenever the logarithmic mean is not sufficiently accurate, the mean driving force may be determined by methods of graphical integration which are beyond the scope of the present paper but which may be worked out by application of principles set forth by Walker, Lewis, and McAdams (11).
LITERATURE CITED (1) Byrne and Carlson, M.S. Thesis, Mass. Inst. Tech., 1921. (2) Cantelo, Simmons, Giles, and Brill, ISD. EICG.CHEM.,19, 9S9 (1927). (3) Greenewalt, Ibid., 18, 1291 (1926). (4) Harte, Baker, and Purcell, Ibid., 25, 528 (1933). (5) Haslam, Hershey, and Keen, Ibid.,16, 1224 (1924). (6) Lewis, Ibid.,8, S25 (1916). (7) Monaweck and Baker, Trans. 4 m . Inst. ChenL. Eng., 22, 165 (1929). (8) Payne and Dodge, ISD. ENQ.CHEM., 24,630 (1932). (9) Riou, Compt. Tend., 174, 1017 (1922). (10) Sieaerts and Fritasche, 2. anorg. allgem. Chem., 133, 17 (1924). (11) Valker, Lewis, and McAdams, “Principles of Chemical Engineering,” Chap. 19, McGraw-Hill, 1923. (la) Whitman and Davis, IXD.EKG.CHEY.,18, 264 (1926). (13) Williamson and Mathews, Ibid., 16, 1157 (1924). RECEIVED April 13, 1933. Presented b y C. R. Harte, Jr., in partial fulfilment of the requirements for t h e degree of doctor of philosophy, Department of Chemical Engineering, University of Michigan.
Effect of Tar Acids upon the Wetting of Wood by Coal-Tar ‘Oils F. H. RHODESAND IRAERICKSON, Cornel1 University, Ithaca, N. Y.
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HEN the individual components of coal-tar creosote oil are tested in the laboratory, the neutral hydrocarbons show fungicidal powers of the same general order of magnitude as those of the phenolic compounds of similar boiling points (1, 6). These results might seem to indicate that the presence of tar acids in creosote oil is not essential and that a neutral or “dead” oil from coal tar would be a t least approximately equal in efficiency to a coal-tar creosote oil of similar distillation range containing tar acids. This conclusion may not be fully justified. It is conceivable that phenols, by aiding the wetting of the wood or by retarding the volatilization of the hydrocarbons, may be desirable components of creosote oil, even though the phenols themselves do not have any specific or unusually high fungicidal power. Rhodes and Gardner showed that phenol vaporizes much less readily from wood pulp than does naphthalene and concluded from this that wood is more ceadily wetted by phenol than by naphthalene and that the phenol is more strongly adsorbed on the wood fiber. They did not, however, make any measurements that indicate quantitatively the effect of tar acids on the wetting of wood by oils.
EXPERIMESTAL PROCEDURE I n the present investigation the relationship between the concentration of solutions of tar acid in aromatic hydrocarbons and the heat of wetting of dry wood pulp by such solutions has been determined. The Jyood used was mechanical pulp from Korway spruce. Approximately 15 grams of the pulp were disintegrated in water and pressed into a mold so as to give a compact cylinder 2.4 em. in diameter. This was then dried thoroughly a t 105” C. and stored in a desiccator over phosphorus pentoxide. A cylinder of the dry wood and a thin-walled glass bulb containing 50 cc. of the liquid of which the wetting power was to be measured were placed in a Bunsen ice calorimeter, on the outside of the inner jacket of which a layer of ice had been frozen. The calorimeter was packed in ice and allowed to stand for a t least 12 hours until uniform temperature was attained and until the water in the capillary was dropping uniformly and very slowly. The thin bulb containing the liquid was then broken and the liquid was allowed t o flow over and saturate the wood. Readings of the height of the water in the indicating capillary were taken a t 5-minute intervals until a qlight and constant rate of change was again attained.
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