SEW BOOKS Mechanochemistry a n d the Colloid Mill. By Pierce .If. Tiai’is. 2.3 X 16 on;11)). f.91. ,Yelc York: The Chemical Catalog Co., 1928. Price:S4.00. At first sight it looks as though colloid chemistry were developing so rapidly that one form of mechanical disintegration had become a book in itself. -1more careful examination shows that about I 56 pages are devoted to colloid chemistry and about twenty-four to the colloid mill. That is more than anybody else has ever devoted to it; but it is not such a tremendous jump as it seemed a t first. The chapters are entitled: introduction; the colloidal state oi matter from the physicalchemical viewpoint; the elementary structure of matter; the relation of viscosity and plasticity to the colloidal state; adsorption; electrical concepts and their importance in colloidal dispersion; the meaning of hydrogen-ion concentration and its importance in colloidal dispersion; orientation; gel structure and the Donnan theory of membrane equilibrium; the protective action of colloids in dispersion; the dispersion of solids and liquids in p s ; the theory of emulsions and emulsification; dispersion of solids and liquids in Liquids; the colloid mill and some of its applications; laboratory methods and physical testing of properties. “Adsorption is an important factor in the wetting of some solids by liquids. If the solid particles are finely divided, they usually have a cushion of air about them, and when the fine powder is put into the liquid, the particles are airbound. That is, the little particles carry the air in v i t h the powder, due to adsorption. This air may afterwards be displaced very slowly and thiq brings in the time factor. While we do not know what factors determine the amount of water adsorbed on fine crystals, there is no doubt but that different degrees of adsorption take place with various substances, hence the wetting power is entirely different. Some substances are easily wetted while others are resistant to wetting and, in a great number of instances, due to the affinity they have for adsorbing air upon the surface of the particle, the particles do not come in contact after the powder is agitated in the presence of such liquid. An excellent example of this is in the case of very finely divided calcium carbonate. If this is added to water and agitated, one may obtain a thick paste after the addition of about z j per cent of carbonate, If this material is then passed through a so-called colloid mill, it is possible to shear off the air cushions and get a proper contact angle of the water with the powder. This dispersion, upon discharge from the colloid mill, will be found to be very fluid again, due entirely to the elimination of the air cushions. .In additional 2j per cent of calcium carbonate can then be added to the dispersion and the operation repeated. A material will be obtained which is a t least j o per cent calcium carbonate and yet very fluid. This demonstrates that the original pasty condition was caused by the adsorption of air on the fine particles. Once this wks eliminated and the liquid brought in true contact with the surfaces the dispersion was again quite fluid. Similar experiences are encountered nith a w e a t number of instances in a finely divided state. With the usual methods of mixing it is impossible to release the air cushions from the finely ground particles, but through proper mechanical treatment these may be removed and a large amount of such substance incorporated into the liquid medium. This is all due t o the adsorption and the elimination of air from the surface oi the finely ground solid material. Once it is wetted with the vehicle it will remain in a finely divided condition, provided there is not present an ion of opposite charge or some other condition of this sort to cause flocculation,” p. 45. One wonders whether this means an error in Bingham’s determinations of zero fluidity. “Frequently, in colloidal dispersion, it is noticed that the material goes into the so-called colloid mill quite thin but is discharged from these mills in a thick condition, with more or less of a gel structure and the material is really plastic. This is always a pleasing indication to the operator of the machine and is usually attributed to fine dispersion, which is partially true. Xevertheless, the product must be in condition to have proper water adsorption or one Ivould not get this gelatinous appearance,” p. 89. “The first users of pressure homogenizers were in the dairy industry. This use dates back to about 190j, when the homogenization of such dairy products as evaporated milk
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and light creams was accomplished by such means. Its purpose was just the reverse of that of a cream separator. Instead of separating thc fat from the milk, it was possible with the homogenizer to incorporate fat into milk, thereby making any percentage of rream desired up to as high as 40 per cent, or what is known as heavy cream. I t is a well-known fact in the dairy trade that homogenized cream cannot be whipped when prepared under regular conditions, such as the pressures above cited, nor will the fat separate out when passed through a cream separator. In other words, by this means one obtained almost a perfect emulsion of milk or cream.” “After the homogenizer had been used successfully in this field for a few years, it was next introduced into the ice-cream industry where it was used to incorporate the fat, milk solids, etc., into a homogeneous mass and develop 3 smooth ice-cream. thus bringing about a big improvement in the product. The practice of homogenizing was confined to the tTvo above-mentioned industries for a number of years. I t was then adapted by the pharmacist to the making of various types of emulsionq such as cod-liver oil. mineral oil-agar emulsions, etc. These machines made fairly satisfactory emulsions of the oil-in-water type for pharmaceutical manufacture and in the preparation of hand lotions and various face creams,” p. I 18. ‘ W h a t the colloid mill really does is to deflocculate and, with a great number of suhstances, this is all that is necessary. This point might be illustrated with the dispersion of zinc oxide. It is well-known that when this substance is first manufactured, it is in a very finely divided s t a t e w h a t might, for commercial purposes, he rlassed as a colloidal state. I n the packing of this product it groups or bonds together, so that the when the paint manufacturer uses it, all that is necessary is to deflocculate it in the presence of some vehicle. This is where the colloid mill is of value, for by dispersion through such a mill it is possible to obtain intimate contact of the vehicle with the small indi\?dual particles of the oxide. eliminate the air cushions brought about through adsorption, and replace these with direct contact of the vehicle with the power. in other words, increase its wetting power. Once these particles are deflocculated and are well wetted by the vehicle the dispersion is satisfactory for commercial application. “This statement also covers LI great number of other instances where it is sometimes said that the product is ground. One can readily prove this point by attempting to disperse carborundum or fused silica, where real grinding or disintegration would he necessary. “It is hoped that this statement will help clarify the situation and d l emphasize the point to prospective users, that if it is a case of deflocculating. the colloid mill may he of value t o them, as it has proven to a great number of manufacturers. If it is a grinding problem, where it is necessary to really disintegrate or grind, no colloid mill has as yet been built which will do such work. Of course, as time goes on, it may be that it will be made possible to really grind by use of a colloid mill of the continuous type. From preserlt evidence and study of the matter, however, the author is of the impression that in order to accomplish this it will he necessary t o have enormous peripheral speeds, much beyond the mechanical limits of the continuous types of mill a t the present time. The above facts, however, have not handicapped the progress of the colloid mill, which has found wide application throughout the chemical industry in various fields of operation,” p. 149. “The colloid mill is very frequently used as a sort of finishing mill the product having been previously treated through some other type of equipment, or else mixed thoroughly in some mixing device so that the colloid mill can handle the product. obtaining a n unusually fine finish with large capacity. There might be other equlpment which would accomplish the same work, but not with the same capacity or low cost of operation. I t has frequently been found that vrith a colloid mill a manufacturer may increase his capacity to such a point that he operates this machine a few hours a week where with other equipment performing the same mission it was necessary to operate continuously. As a result, the manufacturer using the colloid mill can lower the cost of production enormougly and undersell his competitor with another type of equipment. “The following are typical examples of some of the uses to which the colloid or dispersion mills of proper design may be put in commercial operation:
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Emulsification of vegetable, animal and mineral oils, resins, and waxes. LIanufacture of water paints, calcimines, etc. 3. Incorporation of pigments in the more fluid enamels and in paints such as outside white and flat white. 4. Homogenizing of fat globules of milk for improvement in consistency and digestibility or for ice cream mix. Preparation of reconstituted milk from milk powder and sweet butter. 5 . Extractions of oils, fats, resins, juices, etc., from vegetable or animal tissues as well as extraction of fibrous materials. 6. Purification of organic chemicals, liquids and solids. 7 . Intimate mixing of creams, sauces and other foodstuffs where perfect blending is required. 8. Dispersion of some solids such as mica, certain oxides, fine clays, various dyes and other such materials which do not require the actual grinding operation. “Many mineral colloids such as ferric hydroxide, silica gel, etc., contain water which is driven off on heating. Such material then becomes incapable of dispersion or suspensionfor example, a clay heated above 100°C. Up to this temperature the natural moisture may he driven off, hut there may be water of constitution, or that which is chemically combined. and after this is driven off. the residue no longer has the properties of the original material. Therefore, such material before excessive heating might disperse readily with the colloid mill, but surh heating may make dispersion impossible. This, of course, is not always the case for there is no difficulty in dispersing a highly calcined magnesium oxide. I n fact, this is a commercial process for making milk of magnesia. There are, however, a great number of substances to which this rule applies, especially those containing silica, iron etc. Very satisfactory dispersions have been made of chrome yellow, iron and zinc oxide, umber, lamp black, etc., of course, with the addition in most instances of a protective colloid,” p. 164. There is probably a misprint of wool for rayon in the statement, p. 47, that wool adsorbs relatively few basic dyes. This is distinctly an interesting book. I t gives a satisfactory outline of colloid chemistry from the non-teaching standpoint. Wilder D. Barinoft I.
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A Guide to the Literature of Chemistry. B y E. J . Crane and Austin M. Patterson. 438. S e w York: J o h n Ii’iley and Sons, 2967. Price: $6.00. “The literature of chemistry is like a great, inspiring mountain with a core of rich ore. I t is inspiring because the work of great men, of many earnest ‘investigators, is recorded there. To obtain anything like full profit in its use one must learn how to climb this mountain and must know where and how to dig for the ore he needs. With the help of the many successful chemists who have generously contributed the results of their experience, we have attempted in this book to point the way.” The chapters are entitled: the problem and objectives; hooks; periodicals; patents; other sources; indexes; libraries; procedure. “The question always arises as to how far back one should go in using the journal literature. This of course depends a great deal on the nature of the subject and of the search, as discussed in the chapter on Procedure Ip. 2 1 7 ) . Some searchers consider that it is usually safe to assume that everything of value in the journal literature has been made a part of the book literature after a period of about twenty years. A factor in such a decision is the realization that the development of a science is very rapid, so that much of the older literature is now close to useless because of discredited or a t least greatly inferior methods, changed points of view, inadequate theories, and the like. Some even go so far as to assert that we would be better off if n e could scrap the older literature as it becomes that. There are times when one will feel justified in ignoring all but the more modern literature but to do so always would be a mistake. The older literature is not always valueless by any means and books cannot be depended upon t o glean everything that has a lasting value. Ideas and facts are still to be found there even though the methods, interpretations, and theories may practically all have been outgrown or carried over into the more recent literature. Just as it can be said that the journal literature is never out of date because of the 23 X 16 cm; r i p . c
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continuous appearance of units of it. so it can also be said that the older parts of it arc never really out of date because it is original material. X source book cannot be cast aside nor revised,” p. 32. If one is interested in the theoretical side of a subject, it is absolutely necessary to go back a good many years in the journal literature. -4s a broad statement, only those things get into the text-books which fit into the esisting theory. .Is a typical case, how would an?. student learn from any modern text-book that a difference between solvent and solute was self-evident up to about forty years ago and that it dropped out only when and because the solvent was defined as the component which goes through the particular semipermeable membrane that one is considering? From the reviewer’s point of view one of the most important points in the book is the statement by a phyical and metallurgical chemist, p . z z j , that one should start with the most recent literature and work back. The counter-current method has two advantages. One picks up the references better in this way and is sure to be able to take them up in the reversed chronological order. The great advantage, however, is that one reads the earlier literature from the most recent point of view, which means that one detects flaws in reasoning of the earlier papers and omissions in the later ones in a way that could not be done otherwise. The authors have got together a lot of valuable data which cannot be fonnd anywhere else. The authors realize, and the reader will, that a study of this book will not in itself make him an expert at looking things up, though it ought to help him a great deal. The authors themselves say, p. 152, that “skill in literature-searching involves skill in index-using and efficient index-using is an art in itself, a thing to be acquired.” They might profitably have added that looking up a subject is a n art in itself and one which calls for special ability as well as much practice. Since a scientific man looks up a subject primarily to find out what is of interest to him, the various n e w services are not and cannot be of much help to the research man though they may be, and apparently are, of great help to the technical man. The authors have written a book vhich is a model of thoroughness from their point of view. Only time will tell whether people \vi11 get value out of it commensurate with the Wilder D.Bancrojf work that the authors have put in.
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Adsorption und Kapillarkondensation. By Erich Hiickel. 22 X 1.7 c i i i ; p p . v i 308. Leipzig: Akadeviische T.erlagsgtsellschnjt, 1928. Price: bound, 20 m a r k s ; paper, 18 marks. The book is divided into three parts: adsorption of gases and vapors by solids; surface tension of pure liquids and the wetting of solids by liquids; capillary condensation of vapors in porous substances. I n Part I the four chapters are entitled: phenomenology and thermodynamics; molecular theory without reference to the nature of adsorbing forces (limiting case of small amounts adsorbed); the electrical significance of molecular forces; molecular theory for the case of large amounts adsorbed. There are three rhapters in Part 11: thermodynamics of the surface liquid-vapor; thermodynamics of the surface (pure) liquidsolid; theories of surface tension. In Part 111we find: introduction and phenomenological; theory of capillary condensation. The author approves of LIcBain’s term ‘sorption’ xhen one does not know whether it is adsorption or absorption, and he believes that one should distinguish betxeen adsorption and capillary condensation; but that is about all that he commits himself to definitely. Perhaps this is too serere. The author believes in the contact angle and that the order of adsorption of a vapor by a solid is either the order of boiling-points or a function of the van der ”iaals ‘a’. He does not always play quite fair. He admits with reluctance that the van der IT-aals formula does not hold quantitatively, especially in the cases of polymerized vapors. Of course, not even van der Waals ever claimed that it would hold for gases like S I O ~ .The difficulty is that it does not hold qumtitatively for any vapor. There are 292 numbered equations and it seems incredible that one could write so much mathematics and say so little that could actually be tested. The author’s acquaintance Tvith the literature is nothing to brag about. I t is hard to see what useful purpose this book will serve. T i l d e r D.Bancroff
