February, 1927
I S D U S T R I A L A S D EATGIXEERING CHEMISTRY
parallel functions. With the weaker gelatin (lower curves, Figure 10) the difference in viscosity of the pair increases with the concentration. Ehidently, the true solution or equilibrium temperature for this group is well below 40” C. The initial viscosities of this pair are practically alike. -It is evident that a concentration of 6.66 per cent at a temperature of 60” C. is not practical for this class of work. From Figure 8 it will be noted that a t a Concentration of 6.66 per cent the differences for type 9gelatin are constant between 40” and 55” C. and for type B gelatin between 50” and 60” C. Accordingly, t h e best a v e r a g e temperature for this concentration lies somewhere between 45 ” and 50’ C. but since the deflection from the straight line at 45” C. in B is not very great and since this temperature falls well within F i g u r e ¶&-Showing Parallel F u n c t i o n the straight-line Portion for C o n c e n t r a t i o n s above 10 Per C e n t of type A gelatin, if a within L i m i t s concentration of 6.66 per cent is to be used the temperature should not exceed 45O
c.
Figure 9 shows curves of two specimens, No. 7573, an average high-grade, and KO. 7639, an average low-grade
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gelatin. Here again the straight line OY,constant difference part of the curve falls between 45” and 55” C. It seems clear that any temperature falling within this straight-line period would be satisfactory for gelatin testing, but in order to show distinctly small viscosity differences, it would be better to choose a concentration of 10 per cent a t temperature 40’ to 45” C., as these conditions provide the widest practical range and have proved to be the most easily duplicated by different observers. This temperature is also one that can be kept more nearly constant under ordinary working conditions, and low-grade gelatins especially are not liable to degrade so quickly at this temperature as at higher temperatures. Furthermore, no special precautions are necessary. The viscosity change under these conditions will not be appreciable for several hours. The containers should, of course, be covered during the holding period in order to avoid loss of water from evaporation. Bibliography 1-Loeb, “Theory of Colloidal Behavior,” p. 282, McGraw-Hill Book Co., 1924. a-Proctor, Rept. Faraday SOC.and Phys. SOC. London, p. 34 (1920). a-Barrett, I b i d . , p. 49. 4-Loeh, o p . c i L , p. 273. &-Briefer. Trans. SOC.Molion Picture Eng., No. 18. 185 (1924). 6-Bogue, “Applied Colloidal Chemistry,” Vol. I, p. 240, McGraw-Hill Book Co., 1924. 09. c i l . , p. 40 ?-Proctor, 8-Harrison, Ibid., p. 58. g-Loeb, op. c i t . , p. 283 10-Bogue, “Chemistry and Technology of Gelatin and Glue,” p. 151, hlcGraw-Hill Rook Co., 1922. 11-Bogue, “Colloidal Behavior,” Vol. I, p. 377 (1924). and Phys. Sor. London, p. 52 (1920). 12-2sigmondy, Rept. Faraday SOC. la-Reiger, Physik., 13, 241 (1913). 14-Fraas, Hatschek, Rept. Faraday SOC.and Phys. SOC. London, p. 31 (1920). l+Bogue, “Colloidal Behavior,” Vol. I, p. 390 (1924).
What Is Chemical Engineering ?’ By Harry A. Curtis STERLING CHEMICAL LABORATORY, YALE UNIVERSITY, NEW HAYEN,CONN.
Early History
HAT is chemical engineering? Chemical engineering is an art which tvas practiced and fairly well developed long before the science of chemistry was spawned. Robert Boyle is usually accused of being the father of scientific chemistry. Some say it was Lavoisier, presumably having in mind the bad end to which the great French savant finally came. Boyle was a t the height of his career about 1660, Lavoisier more than a century later. What of the chemical engineers in 1660? The history of chemical engineering has not yet been written, but it is well known that in 1660 the chemical engineers of the day were planning, constructing, and operating plants according to the best information available. They were extracting metals from their ores by a variety of processes, some of them strictly chemical; they were purifying the metals by subsequent chemical operations; they were manufacturing in quantity and by factory methods such materials as gunpowder, incendiary bombs, saltpeter, several of the common acids and their salts, a variety of paint pig1 Presented as a part of the Symposium on “Chemical Bngineering” before the Division of Chemical Education a t the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 6 t o 11, 1926.
ments, soap, glass, perfumes, alcohol, sugar, and a large number of what we call today, chemical products. They were building and operating furnaces of many kinds, filters, stills, rectifying columns, driers, evaporators, grinders, and other pieces of what we today call chemical plant equipment. Let us grant that these fellows did not know much of the theory of evaporator design; about as much, let us say, as the average chemist does today. Nor were they able to write chemical reactions for the processes which they carried out. But they built chemical plant equipment and carried out chemical processes on a commercial scale just the same. They used what they could of the sciences then available; they drew on the fund of experience which was common in their profession; and when neither science nor experience was available they guessed, and guessed again, just as their successors must do today. But they produced the goods-that is the important point-and, as time went on, they produced them ever better and cheaper. Were they chemists? Well, not of the “pure” variety which traces its ancestry t o Boyle or Lavoisier. Were they engineers? Let us see what we mean by the term. “Engineer = one who carries through an enterprise by skilful or artful contrivance.” These men were certainly carrying
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INDUSTRIAL AND ENGINEERING CHEMISTRY
through enterprises, chemical enterprises we call them today,
at a time when there were no chemists except such as they, and when the science of chemistry was unknown. They
were chemical engineers, and the men who are today carrying through chemical enterprises by skilful or artful contrivance are likewise chemical engineers by profession, however else they may be classified as scientists. Is chemical engineering a ‘(branch of chemistry?” Well, not historically speaking at any rate. Is i t a “branch of engineering?” It is not a “branch” of engineering in the sense of being an offshoot of any other kind of engineering, but is itself one of the first kinds of engineering to be practiced by man, centuries older than electrical engineering, centuries older than the science of chemistry which has so greatly enriched it. Chemical Engineering as an Art
What is chemical engineering? Chemical engineering is the art of manufacturing useful products through the application and controI of chemical processes. In the early days of chemical industry, the art rested entirely on empiric information. There were no guiding principles, save a few mathematical ones of limited usefulness. As the sciences developed, mathematics, physics, chemistry, mechanics, and various others were brought to bear with much success on the problems of chemical engineering. Not all of the progress in chemical engineering came, however, from utilization of the rapidly growing sciences. Experience with an ever increasing number of chemical processes naturally enriched the fund of empirical data and refined the technic of operation. Better and better chemical equipment was evolved, partly because of a better understanding of the principles involved, but largely through a cut-and-try procedure, or what someone has called “fumbling and success.” Chemical Engineeringas a Science
Gradually i t became evident that in order to meet the requirements of intelligent and skilful engineering in a chemical industry of increasing complexity it would be necessary to coordinate and arrange conveniently the fundamental data applicable in this field. It was realized that every one of the long used operations of chemical industryfiltering, evaporating, drying, distilling-must be investigated carefully in order to discover the fundamental principles involved, and with the ultimate aim of carrying out these operations better than they had ever been done before. So has developed what we may call the science of chemical engineering. Just where chemical science ends and chemical engineering science begins cannot be indicated, nor is it of the slightest importance to locate an arbitrary dividing line between them, for the natural route to chemical engineering is through the field of chemistry. The important thing is to recognize that there is a considerable body of fundamental principles, laws, and essential facts pertinent to chemical engineering lying beyond the purview of chemical science.
Vol. 19, No. 2
to carry out the proposed process. Not once in a hundred times does the information which comes from the chemical laboratory suffice to indicate the answer to this question. A great deal more information regarding the influence of various factors on the reaction is usually needed before any intelligent decision can be made as to the best procedure from an economic standpoint. And so the problem goes to the development laboratory when chemist and chemical engineer join forces. The objective is always the accumulation of adequate data on which to base choice or design of equipment, materials of construction, operating conditions and, finally, cost estimates. Economy of time, of materials, and of energy in accomplishing a given task is a purpose which runs through all of chemical engineering from first to last. Coordination of the Three Essentials
Chemical engineering is an art whose successful practice is based on the coordination of three essentials: first, knowledge of the pertinent sciences and of the accumulated empirical data; second, skill and ingenuity in applying this knowledge to chemical enterprises; and third, judgment in balancing values against costs. We would call attention to the fact that among the fundamental principles to be taught in college, those concerned with the unit operations of chemical engineering are of importance second to none; that knowledge of the large body of empirical facts and of the accumulated experience of the past is an indispensable supplement to knowledge of the sciences; that information alone is not the whole basis of any kind of engineering, but only one of the prerequisites to the skilful carrying out of enterprises; and finally, that every chemical engineer who practices his profession is destined to consider first, last, and above a11 else the question of costs a t every step in a chemical enterprise. It is not likely that all our courses in chemical engineering will be alike nor is it desirable to have them so, but if we can agree on what chemical engineering is, the courses taught will not vary too widely. Conclusion
Economic Phase of Chemical Engineering
From some of the discussions heard lately one might conclude that the terms “chemical engineering” and “chemistry” were mutually exclusive, and that the interests of chemists and chemical engineers were necessarily inimical. Our own belief is that successful chemical engineers will always be able to qualify as chemists. It would indeed be strange if the chemical engineer should not wish to maintain the closest contact with the science most useful in his profession. Strange if he should not take advantage of membership in a great chemical society, and of association with men whose scientific interests overlap and merge with his own. To say, however, that chemical engineering is a “branch of chemistry,” when chemical engineering must necessarily include a great deal of other sciences, and of empirical data, and of technic, and of economics, all lying outside the field of chemistry, is, we believe, merely giving to chemistry a definition which makes it something else than one of the sciences.
And finally, there is the economic phase of chemical engineering, what C. R. Mann has called the correct appraisement of values and costs, that balancing of value and cost which is the controlling factor in all intelligent production. The fact that a certain chemical product can be formed in a certain reaction is usually determined before the problem comes to the chemical engineer. One part of his job is to decide what it will cost to manufacture the product commercially. This a t once raises the question of how best
Dust Explosions-W. A. Noel, of the Bureau of Chemistry, recently started on a trip through the cotton states of the South to demonstrate methods of preventing dust explosions in cottonseed mills. The cottonseed meal industry has become interested in preventive measures because of a n explosion in a cottonseed oil mill in Memphis, Tenn., last spring, which destroyed the entire plant, causing a property loss of $250,000, the.death of one employee, and injury t o more than a dozen others. Dust resulting from the grinding of cottonseed meal apparently does not have such high explosibility as some other dusts.
