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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 21, No. 2
Importance of Colloid-Chemical and Colloid-Physical Research in Future Problems of the Chemical Industry‘ E. A. Hauser: METALLGESELLSCHAFT A. G.,FRANKFURT A/M, GERMANY
LTHOUGH it must be admitted that the expression “colloid-chemical problem” has been more frequently applied in recent years than ever before, I feel that the colloid chemist is not yet taken seriously in many quarters. This is not astonishing, for the colloid state of matter has been so often identified with our ignorance of the peculiar behavior of such materials and the successful application of this new branch of chemico-physical science has been limited to a small number of industries, industries which flourished for ages before we realized that any such intermediate stage between typically crystalline and molecularly dispersed matter existed. Dven today, when such things have been proved beyond doubt and when we have been able to obtain a considerably better insight into some of the fundamental laws governing the behavior of this “world of neglected dimensions,” as Wolfgang Ostwald so perfectly expressed it, and when some of the largest industries have already benefited considerably from them, I believe that present accomplishments are very meager compared with what we may expect from the future. We must not forget that we are deaIing with a fairly recent development, which has been hampered in many ways by the necessity of educating our minds to new lines of thought and interpretation. If I look back on the achievements of the past and then turn my eyes toward the future, I feel that Ostwald’s terminology needs amendment and that the colloid state of matter may be called “the world of neglected possibilities.” Some of these possibilities I have taken as the basis of this discussion. In order to treat the subject as extensively as possible I shall assume that the reader is familiar with the historical development of Graham’s classical works and the fundamental terms generally used in discussing colloids. The year 1928 is especially interesting in chemical history. One hundred years ago Wohler accomplished a t Gottingen his synthesis of urea. With that achievement he proved that Berzelius’ classical assumption could no longer be maintained a theory which postulated that chemistry can only synthesize inorganic compounds and that the synthesis of organic matter is only possible in a living organism aided by a factor of unknown properties termed “vis vitalis.” Wohler’s discovery was a milestone in the development of chemistry, for it was due to this research that the old dominating views were suddenly changed, with the result that an entirely new branch of chemical science, organic chemistry, started to develop. The development of organic chemistry has gone far beyond anything Wohler ever would have dared to anticipate when he first visualized his synthetic urea, and so too has colloid chemistry already gone far beyond Graham’s expectations. The last half-century was ruled by the organic-chemical synthesis. If we, however, look upon this development from an absolutely objective point of view, we must admit that further work along lines of synthesizing organic compounds is becoming more and more difficult. But more than that, we have seen repeatedly that in many cases,
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Presented before the General Meeting f Received August 17, 1928. of the American Chemical Society, Swampscott, Mass., September 10 to 14, 1928. 1 Non-resident associate professor of colloid chemistry, Massachusetts Institute O f Technology.
in spite of proper chemical proportions and technic, we obtain substances with entirely different properties than those we were seeking. Organic chemistry, especially in the field of what is generally termed “high-molecular” compounds and in its correlation with biology, seems to have reached a stage where its known methods and classical definitions or interpretations are insufficient for many of our purposes. Inorganic chemistry has also reached the point where it is faced with facts and reactions unexplainable by the laws governing the three established states of matter or by former concepts of atomic and molecular properties. These last words, however, might cause a misinterpretation of the entire problem if the terms “colloid chemistry” and “colloid physics” were limited to Graham’s differentiations in regard to dialyzability, etc. These limitations would make all further interest more or less futile and could be compared with a very short but actually valueless prolongation of life by applying some kind of injection to momentarily prolong the life of a dying man. To obtain a complete insight into the importance of the chemistry and physics of colloids-I prefer this expression, as chemistry and physics are equally important and indispensable in this field-it seems essential to include all observations and technic which today can in any way influence the colloidal state of matter. The number of tools available to us for this use is increasing daily. Practical Problems for Colloid Research
I n this connection not only the degree and state of dispersion, but also the actual shape of the colloidal particles has a very important bearing on final properties. Before discussing any present knowledge let me cite a few cases. I feel that questions as to whether in soap solutions we have to deal with true or colloidal solutions are of minor importance compared with the reasons for the surface tension and differences in lathering properties, etc., which to a great extent have been found to be related to the shape of the dispersed phases. However important and interesting the “thixotropic” behavior of certain colloidal sols may be, all the more valuable would be an answer to the “why’s’’ of such a unique property, a property which seems to be frequently found in biologically important substances. In the field of ore flotation, although a tremendous amount of research has been carried out with the idea of obtaining a clearer picture of this phenomenon, our knowledge is still scanty. We have learned empirically to float ores in various ways; we have found means of obtaining differential flotation; but we have not yet discovered why the presence of small traces of colloidal matter can make all our efforts futile and render impossible the flotation of some ores. Another important problem is lubrication and greasing. We have learned a great deal about the chemical constitution of various lubricants; we have evolved very ingenious tests for such materials; but we have only just obtained our first insight as to why one substance should be classified as a good and another as a poor lubricant; and we have not done much to ascertain whether the lubricating properties depend on a few specific chemical compounds or are governed by molecular arrangements or intermolecular reactivities. Such investi-
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gation, however, will not only contribute to a deeper understanding of these phenomena, but will undoubtedly open up entirely new viewpoints, which will prove of considerable value in new fields. A field of no minor importance is that of natural fibers. The study of the chemical constitution of these substances has considerably increased our knowledge and has aided in the evolution of such processes as the manufacture of artificial silk. Our ignorance, however, as to the manner in which nature connects these discrete particles in silk, cotton, wool, wood, etc., has so far prevented us from reproducing the main property-the tensile strength. Only when we know how this can be done will we be in a position to find ways and means of increasing one or the other property to a maximum, without losing other valuable and essential properties. We could continue enumerating problems out of almost every industry and demonstrate thereby the amazing deficiency of our past methods and interpretations. The reason for this deficiency seems to me to lie in the fact that until recent times colloidal knowledge has found little real practical application and the research carried out in scientific institutions has been limited mainly to the most simple systems, which, although of great importance to a fundamental understanding of colloidal matter, were of little practical value. It is only in the last few years that a few research workers have definitely broken with such conservative attitudes and have dared to attack extremely complicated industrial problems with ideas and methods which have proved satisfactory in simpler systems. They have dared t o transplant their somewhat fantastic, if viewed with the eyes of a chemist of the older type, conceptions from simple systems and laboratory experiments into industry, and the results have proved that the future of chemical industry will depend not only on a thorough knowledge of inorganic and organic chemistry, physics, and in many cases mathematics, but also largely on a knowledge of colloids, a branch of science which today is wrongly subordinate in many cases to older viewpoints of chemistry and physics. To be able to grasp the chemistry and physics of colloids and to make the most possible out of them one must first have a fir? foundation in chemistry and physics.
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phase, the development of an internal structure causing elasticity. All living protoplasm shows typically elastic behavior, but more than that, it shows a thixotropic effect, to which I have previously referred. It has thus far been possible to copy this phenomenon with a few inorganic and organic sols by adding small traces of electrolytes. Such a sol, for example ironoxyd to which sodium chloride has been added, will set to a pasty gel of marked elasticity, but can be brought back t o a liquid sol by simply shaking, a procedure which can be repeated indefinitely. We have, furthermore, been able to hasten or retard the setting time by various additions -e. g., amino acids are strong retarders, whereas platinum and an electric current are accelerators. Here again the microscope shows the formation of threadlike aggregates densely packed to form parallel bundles of lamellae. The reason for this arrangement is still to be explained, but the amazing relationship to biological problems, the fact that i t has been proved that cell tissues, like muscles (so far believed to be built up by fibers), are more or less thixotropic gels, and the known changes protoplasm undergoes by various influences-all demand a systematic continuation of colloidal research. This may once more emphasize the question-what is life?-to which we still have to reply with the same ‘5gnorabimus” as did Du Bois Reymond in his classical speech in the Leibnitz meeting a t the Berlin Academy of Science in 1880. As indicated before, the phenomena governing lubrication presumably are related to surface effects. Recent extensive research has been carried out which has not only proved this conception, but has opened up entirely new aspects. X-ray analysis has revealed that in all substances having a pronounced lubricating effect pressure causes a molecular rearrangement, resulting in an orientation exercising a t the same time a resistance to the pressure. The molecules then stand perpendicular to the surface the lubricant is supposed i o cover, thus neutralizing the molecular field of force of the surface. At the same time they orientate themselves in parallel lines so that the total energy of such a system is reduced to a minimum. I n the case of a symmetrical molewle such as that of a saturated hydrocarbon, we obtain a monomolecular layer of weak adhesion, as no free ends possessRecent Developments in Colloid Science ing a field of force are available. Asymmetric acids or triSo much for my introductory picture and the development glycerides, however, caClse the formation mostly of bimoof my main thesis that we have a right to expect colloid sci- lecular highly adhesive layers. X-ray analysis, one of the ence t o explain many of the unknown properties of matter. most important tools in colloidal science, combined with a This will be done with the aid of an ever increasing number somewhat new conception of the importance of asymmetric of tools and perfected technics. Perhaps we can best visual- dipolar molecules, has greatly aided in interpreting this ize the probable trend of the immediate future by running surface phenomenon. Why should the method not be equally over a few of the developments of the recent past in con- applicable to ore flotation? It does apply, but the experimental difficulties are tremendous and it may be years before nection with the application of colloid science to industry. I n the soap industry we know that the consistency or actual results will be available. But the possibilities can “structure” of a soap can be materially changed by changing no longer be denied and the results will be without doubt the titer of the fatstock used. At the same time we find that some compensation for the time and money spent, just as a closer study of the colloidal contamination of ore flotation in some cases we can obtain entirely different properties-e. g. difference in elasticity-without changing the titer. It has will solve that problem with advantage to that industry. also been known that by mixing diluted sols of viscous but It is difficult to predict how, but I shall not be surprised if non-elastic nature we obtain sols showing highly elastic the fact that certain colloids can be coagulated out of a properties. For example, when mixing sodium oleate and dispersion by radiation of specific wave lengths will have sodium stearate, ordinary chemical analysis gives no clue as some bearing upon this field of future research. t o the reason for this marked change. An ultra-microscopic One of the most difficult points in regard to this problem examination, however, immediately discloses that the oleate of studying surface effects during flotation by x-rays may be solution is optically empty or homogeneous, whereas the our very scanty knowledge regarding the interpretation of stearate solution shows small twinkling particles. Upon liquid x-ray diffraction patterns. But here I feel confident proceeding further the mixture shows the appearance and that in the not too distant future we shall be able to interpret growth of an enormous number of fine threads forming an liquid patterns with the same ease and accuracy with which irregular but persistent sort of network. In short, we observe we can evaluate crystal lattices today. Oriented coagulation the appearance of what has been termed a i‘mesomorphicJ’ or orientation of liquid molecules of dipolar character, either
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by electric or electromagnetic means, certainly should be more considered in this respect. This will need a revision of our present conception of so-called structureless or amorphous matter. But this revision having been realized, I do not doubt for a moment that the result will be as fruitful as Arrhenius’ theory of ions, a theory which when first published did not greatly increase the scientific esteem of its mental father. The value of applied colloidal knowledge may be demonstrated by a simple experiment. If we compare a rubber cement such as is obtained by dissolving milled rubber in an organic solvent to a concentration of 5 per cent rubber and natural rubber latex of 35 per cent rubber content, we find that the latter has the lowest viscosity. If, however, we dip a mold into such a solution and dry the adhering film, we find that the film obtained by the latex dip is considerably thinner, owing to the poor adhesion of this type of water dispersion. This known factor has been a considerable drawback in some lines of latex application. A close study of the colloid chemistry of rubber, however, has shown us various ways of overcoming these difficulties. For example, by dipping a mold, which is covered with a varnish which will act as a coagulant, into the latex, the non-adhesiveness of the water phase may be replaced by the effect of coagulation of the dispersed rubber. The result is a reasonably thick uniform coating in one operation. Just a few words in regard to the most recent development in structure research, a line which I have already emphasized as being of the greatest importance in attempting to imitate nature, not only chemically, but also in building up compounds from a structural point of view. It has finally been possible, after long and extensive work, to obtain a picture of the structure of cellulose which will meet any demand in regard to chemical reactability, etc. It has been ascertained that two glucose radicals joined in a 1-4 link, and therefore present in a digonal helix configuration, cause the appearance of what we term “identity periods” in x-ray analysis of fibrous materials. We have, furthermore, considerable evidence that such celluIose double rings are linked up to form straight main-valency chains and that 40 to 60 of these chains lined up parallel are held together by micellar forces, thus forming a cellulose particle. In my opinion the most important concept which can be arrived at, and the only one I shall mention here, is that nature makes a preferential use of the principle of building
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UP in the form of main-valency links to long chains. I am even convinced that the future will prove that the linkage of amino acids in proteins is another example. Furthermore, Emil Fisher’s now practically discarded experiments seem to lead to this conclusion. Rubber in stretched condition is another example of the validity of such a conception, which is especially valuable because rubber when stretched to a maximum will behave similar to a natural fiber. This work, however, necessitates a somewhat different attitude in regard to terminology than has been assumed in recent years, especially when talking of molecules. The term “molecule” should only be used for substances that can be isolated in the pure state and properly identified. One is entitled to talk of a cellobiose or glucose molecule, but not of a cellulose molecule. A hexose would be a main-valency chain of linkedup glucose radicals and a cellulose micella is composed of main-valency chains closely packed and attached one to the other by micellar forces. One can talk of an isoprene, perhaps of a dipentene, molecule, but to talk of a rubber molecule means nothing, as the dimensions of such a thing depend on factors beyond our control. This main-valency chain formation can extend in one, two, or three directions into space, and differs distinctly from the so-called molecular lattices of some organic substances derived by simple association forces. In the present case the link is a chemical one, which also explains simply the heretofore unexplainable differences in behavior towards solvents, reactabilities, etc. A closer and still more detailed knowledge of structures and their bearing on properties is, however, essential for a thorough understanding of this class of natural colloids, which have so unique a value in the today’s industries and in life in general.
Conclusion
I hope that I have been able to emphasize your interest in a branch of science which is still in the midst of its childhood, a branch which will need as much attention t o grow as a child in becoming a valuable member of society, and may demand a considerable change in our present conceptions, just as the youth of today has forced many a parent to change his way of looking a t things, in short a branch whose maturing will aid in the development and growth of science and industry, just as we all hope that our children will become valuable factors in the future of our country and of the whole world.
Thermal Characteristics and Heat Balance of a Large Oil-Gas Generator’ Robert D. Pike and George H. West 4068 HOLDEN ST.,EYZRYVILLE, CALIF.
N T H E Pacific coast, except in Washington, manufactured city gas is made largely from California residuum fuel oil. This also applies in other scattered localities in the United States. The generators used are large and operate with low maintenance and labor costs. The large quantity of oil available a t the present time gives this process considerable interest. This article presents the results of a five-day test conducted on a large gas generator of the Jones type, one of a set of five operating a t the Potrero, San Francisco, plant of the Pacific Gas and Electric Company. The generator is illustrated in outline in Figure 1, which shows the relative dimensions of the two connected shells,
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Received May 16, 1928.
which are filled with checker brick. The cycle of operation is 20 minutes long and consists of three periods-the make, the blow, and the heat. The make lasts for 10 minutes. During this period oil and steam are introduced a t several points in each shell, passing downward in each, and gas is removed through the offtake of the secondary shell t o the wash box, where the temperature is lowered to slightly above atmospheric, and lampblack and tar are removed from the gas stream. The blow lasts approximately 5 minutes and is intended to burn out carbon deposited in the generator during the make. The oil feed and the greater part of the steam are shut off, and air is blown in at the top of the primary shell,
