850
ISDUSTRIAL A1VD E S G I S E E R I S G CHEMISTRY
minate, it would have been necessary to use 174 p. p. m. instead of the 44 p. p. m. used in test Id.” On page 639, column 1, line 14, the statement: “With equivalent sodium contents, the added silica reduction is shown to be due to the presence of alumina” should have read: “Even with a reduced sodium and equivalent alumina content, the increased silica precipitation by sodium aluminate shows strikingly the influence of alumina in silica removal.’’
tivity
(:)
T-ol. 23,
KO.7
based upon weight of cake in the press rather than any
consideration of volume or thickness. Xumerous investigators have observed that filter resistance is determined to a large extent by particle size. Hatschek [ J . SOC.Chem. I d . , 29, 538 (1908)] expressed the belief that a microscopic examination of precipitates should be of considerable aid in predicting 1 filter behavior. -- as defined above has a very definite physiCY
cal significance and can be shown from theoretical consideraC. H. CHRISTMAS R26vy~ . A knowledge of the J. A . HOLMES tions to be a factor of the form H. THOMPSOK mean square radius of the particles in a suspension, their density, the pore volume with which they form a cake, a shape factor f , and a universal constant K should make i t possible to calculate from a theoretical basis the filter behavior of any suspenComments upon Recent Developments sion of solid matter in a liquid. Obviously, it would be a difficult task to measure these separate factors compared to the determinain Theory of Filtration tion of their product by means of a simple filtration test. However, the fundamental correctness of the relation and of this conEditor of Industrial and Engineering Chemistry: ception of filter resistance can be demonstrated very nicely by In the light of some recent papers by van Gilse, van Ginneken, studying the flow of liquids through layers of material such as quartz grains or crushed rock. and Waterman [ J . SOC.Chem. I n d . , 49, 444T, 483T (1930); 50, (4) The fact that there exists no sharp dividing line between 41T, 95T (1931)] upon the subject of filtration, it seems advisable the sludges commonly regarded as non-compressible and those to call attention to an extensive program of research in the same which are highly compressible. Thus Equations 1 and 2 govern the entire range of filter behavior in a manner of extreme simfield which has been carried out in these laboratories during the plicity as compared t o former equations (LValker, Lewis, and Mcpast two years and will be published as soon as released by the Adams, Zoc. cit., p. 366). faculty of the Graduate School of the University of Minnesota. (5) Recognition of the fact that non-proportionality between The authors cited worked a t constant pressures with a small rate of flow and pressure is due to an actual compressibility of suction filter having an area of 43 sq. cm. upon suspensions of dif- the filter cake which is a simple h e a r function of the pressure rather than a power function for constant pressure filtrations. ferent kinds of charcoal, over a pressure range of 0.2 to 0.7 kg. per -A theoretical basis for this has been derived which is confirmed sq. cm. (2.845 to 9.96 pounds per square inch). They concluded by our own researches and by the work of van Gilse, van Ginneken, and m’aterman. that the resistance of their filter cakes could be expressed as a linear function of the pressure-e. g., r = ao(1 pP)-a form Filtration tests have been made upon such materials as Sil-0which possesses decided advantages over the accepted Lewis Cel, calcium carbonate, calcium sulfate, ferric hydroxide, and equation (Walker, Lewis, and McAdams, “Principles of Chemical Engineering,” p. 366, McGraw-Hill, 1927) where r is considered lead chromate, using cotton cloth, monel metal cloth, and Filtros plate filter septums in a small-size filter press (9-inch diameter to vary as In the course of the work performed in these laboratories, modi- frame) with available pressures up to 60 pounds per square inch. The three different methods of performing filter tests-that is, fied equations governing filtration have been developed and a constant pressure, constant rate, and constant resistance-have number of methods worked out for analyzing the data of filter tests, It has been found that the following equations, based upon been investigated. For slightly Compressible material, the constant rate method Poiseuille’s law, are of general applicability : is superior for a number of reasons: ~
+
Equation 1 is the fundamental equation governing filtrations a t constant pressure, and Equation 2 is the form governing filtrations a t constant rate. The nomenclature is largely that of Walker, Lewis, and McAdams (Zoc. cit., p. 363) plus the addition of several new symbols. Success in this work has been due in large measure to the following nex conceptions and methods of treatment:
.
(1) The development of methods whereby the resistance offered to flow of filtrate by the supporting filter base can be separated from that of the filter cake proper in the treatment of data. It is because van Gilse, van Ginneken, and m‘aterman, in the work supporting their thesis, used a filter cloth of unusually low resistance (practically zero) compared to that of the filter cakes, that they were able to arrive a t their conclusions. When they made a similar filtration in a commercial-size press, they were forced t o conclude that it did not obey the same laws that governed filtrations in the suction filter. It can be shown easilv that in the latter test the resistance of the filter cloth was of more nearly normal proportions, and that when it is properly accounted for, the observed data do not depart more than 0.2 per cent from the theoretical behavior. 1 - 7s , whereby filtrate (2) The introduction of the factor ~
PS
volumes become a definite measure of the weight of filter cake in the press a t any time. (3) The conception of a specific cake resistance ( a )or conduc-
(1) h constant rate of filtration can be maintained with greater accuracy than can a constant pressure. (2) The small but unavoidable errors always present in constant-pressure filtrations due to turbulent flow of filtrate in the leads are avoided because in this method the pressure drop through the leads remains constant and can be measured. (3) The relation of resistance to pressure is given in a single test, whereas by constant pressure methods a number of tests must be made a t intervals over the desired pressure range. (4) The compressibility relation thus found is an average value which can be rechecked again experimentally with much greater accuracy than can any single value obtained by constant pressure test. The constant resistance method-i. e., a test conducted by running pure water through a cake previously laid down by a filtration-while theoretically the easiest method of carrying out a filter test, and capable of the greatest accuracy, is actually not a valid measure of any filter behavior. It is in large measure tests of this nature which have confused the minds of experimenters from 1912 to 1931 and which account for the differences in opinion from time to time as to whether pressure occurred in the filtration equation to powers of l / 2 , 1, 2, or decimal fractions. This phenomenon, which always seems to mask filter test constants when water is later passed through the cake, obeys a law just as definitely as does the filtration. Lacking its applications, many data in the literature obtained by running water through a filter cake or even a clean cloth, and utilized to determine filter behavior, have led to erroneous conclusions. It can be said with assurance that no other branch of chemical
July, 1931
I-YDCSTRIAL A S D ESGISEERISG CHEXISTRY
engineering lends itself more exactly t o theoretical treatment and mathematical analysis and computation than does this much maligned unit process of filtration. The literature contains numerous examples of very careful work which lacks only the correct interpretation to prove this contention. From the first published filter tests of Lewis and Almy [J. IND.EX. CHEM.,4, 528 (1912)l upon chromium hydroxide to the latest work of van Gilse, van Ginneken, and Waterman, who were unable t o interpret the data obtained from the filtration of 100 liters of eponite (Table XXXIII, p. 98T), the
551
analysis by Equation 1 shows splendid agreement. This will be demonstrated during the course of a series of papers to appear in the near future. B. F. RUTH R. E. MONTONSA G. H. I M DIVISION OF CHEMICAL EXCXNEERINC OF CHEMISTRY SCHOOL UNIVERSITY OF MINNESOTA MINK. MINNEAPOLIS, April 27, 1931
BOOK REVIEWS A Monograph on Viscometry. BY GUYBARR. 316 61/4 X 10 inches. $12.00.
-+
xiv pages. Oxford Cniversity Press, 1931. Price,
Doctor Barr adheres closely t o his subject and does not consider such matters as the relation between viscosity and chemical composition or even the change in viscosity with temperature, usually contained in books on viscosity. This is the most complete work available on the viscometry of liquids, and the viscometry of gases is treated briefly but adequately. -4bout half the book is taken up with the theory, design, and use (of capillarytube instruments, with a description of the Vogel-Ossag viscometer for the first time in English. The flow between parallel planes, the Michell viscometer, rotation viscometers, and miscellaneous other methods of viscometry are discussed. Methods of measuring viscos;ties up t o 1 O l o poises and over are given, although the subject C.I the consistency of solids is omitted as being “too involved.” Unusually thorough is the discussion of the falling-ball viscometer, in which it is pointed out that the usually accepted factor 2.4 in the Ladenburg correction should be 2.1. If it is of questionable advantage to use Couette’s method in absolute viscometry, it becomes all the more important to use calihating liquids of accurately known viscosity. There is common agreement that water is the best such liquid, but it is not so certain that its viscosity a t 20’ C. is 1.009 poise. ‘The author remonstrates a t the neglect of the kinetic-energy correction when needed, but is less definite in regard to the possibility of a rather minor error in erroneously applying this correction. If the correction is zero until R = 10, equations for most technical viscometers can only be justified as the best available. The amount of space, 23 pages, devoted t o colloidal materials seems small in comparison with their importance, but the wisdom of the author in omitting much that may not prove of lasting value can hardly be questioned, even though there are many materials t o which the equations mentioned do not apply.-WrNsLow H. HERSCHEL
instead t o interpret from the layman’s viewpoint all of this information based upon his personal experience, the material might more easily find a real place in the literature of the subject. What is always needed is more and more advice from those having a great deal of successful experience, and therefore, a work of this character, if it is t o be handled by a layman, is usually treated t o much better advantage by one who has actually had a wide and successful experience in the handling of his own patent problems, and who passes on this experience for the benefit of his fellows. The author seems t o have touched upon most of the essential points which might prove of interest t o his readers, and he and the publishers are t o be commended for making th: effort to spread this knowledge where it may best reward the worker and inventor-that is, in the technical field, including those of the chemist and engineer, and their executives.-R.4~ BELMONT WHITMAN Annual Survey of American Chemistry. Volume V-1930. J, WEST. 629 pages. Published by Edited by CLARENCE the Chemical Catalog Company, Inc., New York, 19.31. Price, $5.00.
This is the fifth Annual Survey prepared under the auspices of the Division of Chemistry and Chemical Technology of the National Research Council. I t is the most impressive of the volumes so far issued in this series, comprising with index 629 pages. The subjects treated have been selected from a long list of those possible, and the Committee has endeavored t o assign these topics t o men whose work indicates them t o be specialists in the several fields. It is obviously impossible t o review such a work in the usual sense of the word. Each chapter is intended t o be what the title of the book implies-namely, a survey of the work which has been done by dmerican and Canadian chemists in the designated field during the past year as disclosed by contributions t o the scientific literature. Blthough some of the authors give interpretative explanations, for the most part the Patent Law for Chemists, Engineers and Executives. BY FRED work has been confined t o bringing into logical form for presentaH. RHODES. 207 pages. McGraw-Hill Book Company, tion results that have been reported by the several workers. The bibliography for each chapter is valuable and useful t o all those Inc., hTewYork, 1931. Price, $2.50. working in the same or related fields. In some instances these Reading Professor Rhodes’ book on patent law reminds me of references are very few, one chapter having 393 citations in the the professor a t Carnegie Tech who told his class that the best footnotes. way t o learn a lot about a subject was to write a book on it! The subjects treated are as follows: I-Solutions, Victor K. One thing to be said in favor of the volume is that the author LaMer; 11-Kinetics of Gases and Gas Mixtures, F. 0. Rice; has strayed but little from close adherence to the voluminous de- 111-Subatomic Phenomena, Harold C. Grey; IT‘----Therm3cisions quoted. Therefore, there are relatively few inaccuracies dynamics and Thermochemistry, Frederick D. Rossini; V-Colin the text, so readers may be reasonably sure that the informa- loid Chemistry, F. E. Bartell; VI-Catalysis, Robert N. Pease; tion given is accurate, so far as it goes. VII-Photochemistry, George B. Kistiakowsky ; VIII--Physical The chapter on the patent rights of employers and employees Methods in Analytical Chemistry, E. G. Zies; IX---The Deshould prove interesting and valuable t o technical readers, most termination of Crystal Structure by X-Rays, Linus C. Pauling; of whom are employed by others, and some of whom employ X-The X-Ray Examination of Materials, Arthur W. Kenney ; others. This information, while adequately covered in the litera- XI-Applicstion of Electrochemistry, Oliver Vir, Storey; XIIture already out on patents, is too little known generally and so The Rare Earths, B. S. Hopkins; XIII-Iron and Steel Metalwell bears repetition. It is to be regretted, however, that more lurgy, C. H. Herty, Jr. ; XI\‘-Metallo-Organic Compounds, specific advice of a practical character was not included, both from hl. S. Kharasch; XV-Aliphatic Compounds, C. W. Porter; the standpoint of the employee on what t o do and what not t o XVI-Carbocyclic Compounds, R . L. Shriner; XVII--Heterodo to protect his rights to inventions a t the time of taking a job cyclic Compounds, Hans T. Clarke; XVIII-Carbohydrates, and afterwards, and also from the standpoint of the employer Wm. Lloyd Evans and Melville L. Wolfrom; XIX-Pharmawho is about to hire or has hired an employee for a specific work. ceuticals, Ernest H. Volwiler; XX-Biochemistry, D. Wright Had the author eliminated many of the long quotations of de- Wilson; XXI-Vitamins, H. C. Sherman; XXII-Food;, Icie cisions, which accounts for about half the book, and attempted G. Macy and Betty Nims; XXIII-Water, W. D. Collins and
~
