The 1982 summer school on nuclear physics, organized by the Nuclear Physics Division of the Netherlands' Physical Society, was the fifth in a series that started in 1963. The number of students attending has always been about one hundred, coming from about thirty countries. The theme of this year's school was symmetry in nuclear physics. This book covers the material presented by the enthusi astic speakers, who were invited to lecture on this subject. We think they have succeeded in presenting us with clear and thorough introductory talks at graduate or higher level. The time schedule of the school and the location allowed the participants to make many informal contacts during many social activities, ranging from billiards to surf board sailing. We hope and expect that the combination of a relaxed atmosphere during part of the time and hard work during most of the time, has furthered the interest in, and understanding of, nuclear physics. The organization of the summer school was made possible by substantial support from the Scientific Affairs Division of the North Atlantic Treaty Organization, the Netherlands' Ministry of Education and Science, the Foundation Physica and the Nether lands' Physical Society."

Over the last several years, the field of materials science has witnessed an explosion of new, advanced materials. They encompass many uses and include superconductors, alloys, glasses, and catalysts. Not only are there quite a number of new enhies into these generic classes of materials, but the materials themselves represent a wide array of physical forms as well. Bulk materials, for example, are being synthesized and applica tions found for them, while still other materials are being synthesized as thin films for yet still more new (and in some cases, as yet unknown) applications. The field continues to expand with (thankfully ) no end in sight as to the number of new possibilities. As work progresses in this area, there is an ever increasing demand for knowing not only what material is formed as an end product but also details of the route by which it is made. The knowledge of reaction mechanisms in their synthesis many times allows a researcher to tailor a preparative scheme to either arrive at the final product in a purer state or with a better yield. Also, a good fundamental experimental knowledge of impuri ties present in the final material helps the investigator get more insight into making it."

to the Fundamental and Applied Catalysis Series Catalysis is important academically and industrially. It plays an essential role in the manufacture of a wide range of products, from gasoline and plastics to fertilizers and herbicides, which would otherwise be unobtainable or prohibitive ly expensive. There are few chemical-or oil-based material items in modern society that do not depend in some way on a catalytic stage in their manufacture. Apart from manufacturing processes, catalysis is finding other important and over-increasing uses; for example, successful applications of catalysis in the control ofpollution and its use in environmental control are certain to in crease in the future. The commercial import an ce of catalysis and the diverse intellectual challenges of catalytic phenomena have stimulated study by a broad spectrum of scientists including chemists, physicists, chemical engineers, and material scientists. Increasing research activity over the years has brought deeper levels of understanding, and these have been associated with a continually growing amount of published material. As recentlyas sixty years ago, Rideal and Taylor could still treat the subject comprehensively in a single volume, but by the 19 50s Emmett required six volumes, and no conventional multivolume text could now cover the whole of catalysis in any depth.

This book documents the proceedings of the symposium, "Mineral Scale Formation and Inhibition," held at the American Chemical Society Annual Meeting August 21 to 26, 1994, in Washington, D. C. The symposium, sponsored by the Division of Colloid and Surface Chemistry, was held in honor of Professor George H. Nancollas for his pioneering work in the field of crystal growth from solution. A total of 30 papers were presented by a wide spectrum of scientists. This book also includes papers that were not presented but were in the symposium program. The separation of a solid by crystallization is one of the oldest and perhaps the most frequently used operations in chemistry. Because of its widespread applicability, in recent years there has been considerable interest exhibited by academic and industrial scientists in understanding the mechanisms of crystallization of sparingly soluble salts. The salt systems of great interest in industrial water treatment area (i. e., cooling and boiler) include carbon ates, sulfates, phosphates, and phosphonates of alkaline earth metals. Although not as common as calcium carbonate and calcium sulfate, barium and strontium sulfates have long plagued oil field and gas production operations. The build-up of these sparingly soluble salts on equipment surfaces results in lower heat transfer efficiency, increased corrosion rates, increased pumping costs, etc. In the laundry application, insoluble calcium carbonate tends to accumulate on washed fabrics and washing equipment parts, resulting in undesirable fabric-encrustation or scaling."

Stability constants are fundamental to understanding the behavior of metal ions in aqueous solution. Such understanding is important in a wide variety of areas, such as metal ions in biology, biomedical applications, metal ions in the environment, extraction metallurgy, food chemistry, and metal ions in many industrial processes. In spite of this importance, it appears that many inorganic chemists have lost an appreciation for the importance of stability constants, and the thermodynamic aspects of complex formation, with attention focused over the last thirty years on newer areas, such as organometallic chemistry. This book is an attempt to show the richness of chemistry that can be revealed by stability constants, when measured as part of an overall strategy aimed at understanding the complexing properties of a particular ligand or metal ion. Thus, for example, there are numerous crystal structures of the Li+ ion with crown ethers. What do these indicate to us about the chemistry of Li+ with crown ethers? In fact, most of these crystal structures are in a sense misleading, in that the Li+ ion forms no complexes, or at best very weak complexes, with familiar crown ethers such as l2-crown-4, in any known solvent. Thus, without the stability constants, our understanding of the chemistry of a metal ion with any particular ligand must be regarded as incomplete. In this book we attempt to show how stability constants can reveal factors in ligand design which could not readily be deduced from any other physical technique.

This volume chronicles the proceedings of the Symposium on Metallized Plastics: Fundamental and Applied Aspects held under the auspices of the Dielectrics and Insulation Division of the Electrochemical Society in Chicago, October 10-12, 1988. This was the premier symposium on this topic and if the comments from the attendees are any barometer of the success of a symposium then it was a grand success. Concomitantly, it has been decided to hold it on a regular basis (at intervals of 18 months) and the second event in this series is planned as a part of the Electrochemical Society meeting in Montreal, Canada, May 6-10, 1990. Metallized plastics find a legion of applications ranging from mundane to very sophisticated. A complete catalog of the various technological applications of metallized plastics will be prohibitively long, so here some eclectic examples should suffice to show why there is such high tempo of R&D activity in the arena of metallized plastics, and all signals indicate that this high tempo will continue unabated. For example, polymeric films are metallized for packaging (food and other products) purposes, and the applications of metallized plastics in the automotive industry are quite obvious. In the field of microelectronics and computer technology, insulators are metallized for interconnection and other functional purposes. Also plastics are metallized to provide electromagnetic shielding.

In the last five years, the study of metal hydrides has ex panded enormously due to the potential technological importance of this class of materials in hydrogen based energy conversion schemes. The scope of this activity has been worldwide among the industrially advanced nations. There has been a consensus among researchers in both fundamental and applied areas that a more basic understanding of the properties of metal/hydrogen syster;, s is required in order to provide a rational basis for the selection of materials for specific applications. The current worldwide need for and interest in research in metal hydrides indicated the timeliness of an Advanced Study Insti tute to provide an in-depth view of the field for those active in its various aspects. The inclusion of speakers from non-NATO coun tries provided the opportunity for cross-fertilization of ideas for future research. While the emphasis of the Institute was on basic properties, there was a conscious effort to stimulate interest in the application of metal hydrides to solar/hydrogen energy conver sion schemes in land areas where solar energy has promise as a primary energy source. In addition to the lectures, several seminars were given which treated topics of special interest in greater detail."

Microcharacterization of materials is a rapidly advancing field. Among the many electron and ion probe techniques, the cathodoluminescence mode of an electron probe instrument has reached a certain maturity, which is reflected by an increas ing number of publications in this field. The rapid rate of progress in applications of cathodoluminescence techniques in characterizing inorganic solids has been especially noticeable in recent years. The main purpose of the book is to outline the applications of cath odoluminescence techniques in the assessment of optical and electronic proper ties of inorganic solids, such as semiconductors, phosphors, ceramics, and min erals. The assessment provides, for example, information on impurity levels derived from cathodoluminescence spectroscopy, analysis of dopant concentra tions at a level that, in some cases, is several orders of magnitude lower than that attainable by x-ray microanalysis, the mapping of defects, and the determination of carrier lifetimes and the charge carrier capture cross sections of impurities. In order to make the book self-contained, some basic concepts of solid-state phys ics, as well as various cathodoluminescence techniques and the processes leading to luminescence phenomena in inorganic solids, are also described. We hope that this book will be useful to both scientists and graduate students interested in microcharacterization of inorganic solids. This book, however, was not intended as a definitive account of cathodoluminescence analysis of in organic solids. In considering the results presented here, readers should re member that many materials have properties that vary widely as a function of preparation conditions."

Asphaltenes have traditionally been viewed as being extremely complex, thus very hard to characterize. In addition, certain fundamental properties of asphaltenes have pre viously been inaccessible to study by traditional macroscopic methods, further limiting understanding of asphaltenes. These limitations inhibited development of descriptions regarding the microscopic structure and solution dynamics of asphaltenes. However, a variety ofmore recent studies have implied that asphaltenes share many chemical properties with the smaller, more tractable components of crude oils. Recent measurements have indicated that asphaltene molecular weights are not as arge as previously thought, perhaps in the range of 600 to I 000 amu. In addition, new experimental methods applied to asphaltene chemical structures have been quite revealing, yielding a broad understanding. Conse quently, the ability to relate chemical structure with physical and chemical properties can be developed and extended to the understanding of important commercial properties of asphal tenes. This book treats significant new developments in the fundamentals and applications of asphaltenes. In the first section ofthe book, new experimental methods are described that characterize asphaltene structures from the molecular to colloidallength scale. The colloidal properties are understandable in terms of asphaltene chemical structures, especially with regard to the heteroatom impact on bonding. However, quantitative measurements of the of asphaltene self-association still need to be determined. In the second section of enthalpy this book, the fundamental understanding of asphaltenes is related riirectly to asphaltene utilization."

Mass spectrometry underwent dramatic changes during the decade of the 1980s. Fast atom bombardment (F AB) ionization, developed by Barber and coworkers, made it possible for all mass spectrometry laboratories to analyze polar, highly functionalized organic molecules, and in some cases ionic, inorganic, and organometallic compounds. The emphasis of much of this work was on molecular weight determination. Parallel with the development of ionization methods (molecular weight mass spectrometry) for polar biological molecules, the increased mass range of sector and quadrupole mass spectrometers and the development of new instruments for tandem mass spectrometry fostered a new era in structural mass spectrometry. It was during this same period that new instrument technologies, such as Fourier transform ion cyclotron resonance, radio frequency quadrupole ion trap, and new types of time-of-flight mass spectrometers, began to emerge as useful analytical instruments. In addi tion, laser methods useful for both sample ionization and activation became commonplace in almost every analytical mass spectrometry laboratory. In the last 5 years, there has been explosive growth in the area of biological mass spectrometry. Such ionization methods as electrospray and matrix-assisted laser desorption ionization (MALDI) have opened new frontiers for both molecular weight and structural mass spectrometry, with mass spectrometry being used for analysis at the picomole and even femto mole levels. In ideal cases, subfemtomole sample levels can be successfully analyzed. Sample-handling methods are now the limiting factor in analyz ing trace amounts of biological samples.

This and its companion Volume 2 chronicle the proceedings of the First Technical Conference on Polyimides: Synthesis, Char acterization and Applications held under the auspices of the Mid Hudson Section of the Society of Plastics Engineers at Ellenville, New York, November 10-12, 1982. In the last decade or so there has been an accelerated interest in the use of polyimides for a variety of applications in a number of widely differing technologies. The applications of polyimides range from aerospace to microelectronics to medical field, and this is attributed to the fact that polyimides offer certain desirable traits, inter alia, high temperature stability. Polyimides are used as organic insulators, as adhesives, as coat ings, in composites, just to name a few of their uses. Even a casual search of the literature will underscore the importance of this class of materials and the high tempo of R&D activity taking place in the area of polyimides. So it was deemed that a conference on polyimides was both timely and needed. This conference was designed to provide a forum for discussion of various ramifications of polyimides, to bring together scientists and technologists interested in all aspects of polyimides and thus to provide an opportunity for cross-pollination of ideas, and to highlight areas which needed further and intensi fied R&D efforts. If the comments from the attendees are a baro meter of the success of a conference, then this event was highly successful and fulfilled amply its stated objectives.

The main objective of this book is to systematically describe the basic principles of the most widely used techniques for the analysis of physical, structural, and compositional properties of solids with a spatial resolution of approxi mately 1 ~m or less. Many books and reviews on a wide variety of microanalysis techniques have appeared in recent years, and the purpose of this book is not to replace them. Rather, the motivation for combining the descriptions of various mi croanalysis techniques in one comprehensive volume is the need for a reference source to help identify microanalysis techniques, and their capabilities, for obtaining particular information on solid-state materials. In principle, there are several possible ways to group the various micro analysis techniques. They can be distinguished by the means of excitation, or the emitted species, or whether they are surface or bulk-sensitive techniques, or on the basis of the information obtained. We have chosen to group them according to the means of excitation. Thus, the major parts of the book are: Electron Beam Techniques, Ion Beam Techniques, Photon Beam Techniques, Acoustic Wave Excitation, and Tunneling of Electrons and Scanning Probe Microscopies. We hope that this book will be useful to students (final year undergrad uates and graduates) and researchers, such as physicists, material scientists, electrical engineers, and chemists, working in a wide variety of fields in solid state sciences.

Iron Acquisition by the Genus Mycobacterium summarizes the early evidence for the necessity of iron in mycobacteria and the discovery of the mycobacterial siderophores mycobactin, carboxymycobactin, and exochelin. The structural characterization of the mycobacterial siderophores is described. The genes so far identified as essential for iron acquisition and maintenance of an infection by pathogenic mycobacteria are discussed. The potential role of siderocalin in iron gathering by M. tuberculosis is featured. Because new drugs for M. tuberculosis are needed, this brief also emphasizes the design of antibiotics that interfere with siderophore biosynthesis and the use of siderophore analogs and/or conjugates.

Mechanisms of Inorganic and Organometallic Reactions provides an ongoing critical review of the primary literature concerned with mechanisms of inorganic and organometallic reactions. The main focus is on reactions in solution, although solid-state and gas-phase studies are included where they provide relevant mechanistic insight. Each volume covers an eighteen-month literature period, and this, the eighth volume in the series, includes papers published during January 1990 through June 1991. Where appropriate, references to earlier reports and to specific sections in previous volumes are given. Coverage spans the whole area as comprehensively as possible in each volume, and while it is impossible to be absolutely exhaustive, every effort is made to include all of the important published work that is relevant to the elucidation of reaction mechanisms. Numerical data are reported in the units used by the original authors, and they are converted to common units only when comparisons are being made. The successful format of earlier volumes is retained to facilitate tracing progress over several years in a particular topic, and the series now permits this to be done for a twelve-year period. The introduction three volumes ago of computerized techniques to improve cross-referencing in the Index brought positive reader comments, and their use is being continued.

Science is not a mere collection of facts. It is the correlation of facts, the interpretative synthesis of the available knowledge and its application that excite the imagination of a scientist. Even in these days of modern technology, the need for quick and accurate dissemination of new information and current concepts still exists. Conferences and Symposia offer one direct method of communication. The Summer Schools are another approach. The success of a Summer School is mainly due to that human factor and under standing that goes with it and allows for extensive and often time-unrestricted discussions. During the course of the past 20 years, one of the most in tensively studied groups of elements in the Periodic Table is the Lanthanides. In this period, we have increased our knowledge on these once exotic elements, which were once considered to be a part of a lean and hungry industry, many-fold due to the involve ment of scientists from various disciplines. The purpose of our Summer School was to bring a group of ex perts and participants together for the exchange of ideas and in formation in an informal setting and to promote interdisciplinary interactions. Out of many conceivable topics, we selected the following five as the main basis to broaden our knowledge and understanding I) Systematics 2) Structure 3) Electronic and Magnetic Proper ties 4) Spectroscopic Properties and 5) Lanthanide Geochemistry."

Syracuse University and the Army Materials and Mechanics Research Center of Watertown, Massachusetts have conducted the Sagamore Army Materials Research Conference since 1954. In ce1ebration of the 25th Anniversary of this conference, these proceedings are dedicated to the founding members of the Sagamore Conferences. They are Prof. Dr. George Sachs, Dr. James L. Martin, Colonel Benjamin S. Mesik, Dr. Reinier Beeuwkes, Mr. Norman L. Reed and Dr. J. D. Lubahn. This vo1ume, ADVANCES IN METAL PROCESSING, addresses Rapid Solidification Processing, Powder Processing and Conso1idation, We1ding and Joining, Thermal and. Mechanica1 Processing, Meta1 Removal and Process Mode1ing. The dedicated assistance of Mr. Joseph M. Bernier of the Army Materials and Mechanics Research Center and He1en Brown DeMascio of Syracuse University throughout the stages of the conference p1anning and fina11y the pub1ication of this book is deep1y appreciated. Syracuse University Syracuse, New York The Editors vii CONTENTS OVERVIEW Materials Processing - A Perspective of the Field 1 M.C. Flemings and R. Mehrabian SESSION I RAPID SOLIDIFICATION PROCESSING B.B. Rath, Moderator Heat Flow Limitations in Rapid Solidification Processing . . . . . . . . . . . 13 R. Mehrabian, S.C. Hsu, C.G. Levi, and S. Kou Laser Processing of Materials . . . . . 45 B.H. Kear, E.M. Breinan, and E.R. Thompson Electrohydrodynamic Techniques in Metals 79 Processing . . . . . . . . . . ."

During the past few decades, much research has been reported on the formation of insoluble monomolecular films of lipids and biopolymers (synthetic polymers and proteins) on the surface of water or at the oil-water interface. This interest arises from the fact that monomolecular film studies have been found to provide much useful information on a molecular scale, information that is useful for understanding many industrial and biological phenomena in chemical, agricultural, pharmaceutical, medical, and food science applications. For instance, information obtained from lipid monolayer studies has been useful in determining the forces that are known to stabilize emulsions and biological cell membranes. The current texts on surface chemistry generally devote a single chapter to the characteristics of spread monolayers of lipids and biopolymers on liquids, and a researcher may have to review several hundred references to determine the procedures needed to investigate or analyze a particular phenomenon. Furthermore, there is an urgent need at this stage for a text that discusses the state of the art regarding the surface pheqomena exhibited by lipids and biopolymers, as they are relevant to a wide variety of surface and interfacial processes.

Over the past fifteen years the Commission on Equilibrium Data of the Analytical Division of the I nter national Union of Pure and Applied Chemistry has been sponsoring a noncritical compilation of metal complex formation constants and related equilibrium constants. This work was extensive in scope and resulted in the publication of two large volumes of Stability Constants by the Chemical Society (London). The first volume, edited by L. G. Si"en (for inorganic ligands) and by A. E. Marte" (for organic ligands), was published in 1964 and covered the literature through 1962. The second volume, subtitled Supplement No.1, edited by L. G. Si"en and E. Hogfeldt (for inorganic ligands) and by A. E. Marte" and R. M. Smith (for organic ligands), was published in 1971 and covered the literature up to 1969. These two large compilations attempted to cover a" papers in the field related to metal complex equilibria (heats, entropies, and free energies). Since it was the policy of the Commission during that period to avoid decisions concerning the quality and reliability of the published work, the compilation would frequently contain from ten to twenty values for a single equilibrium constant. In many cases the values would differ by one or even two orders of magnitude, thus frustrating readers who wanted to use the data without doing the extensive literature study necessary to determine the correct value of the constant in question."

Focusing on practical applications, the author provides a balanced introduction to the many possible technological uses of metal complexes. Coverage includes the transition metals, lanthanide and actinide complexes, metal porphyrins, and many other complexes. This volume meets the needs of students and scientists in inorganic chemistry, chemical physics, and solid-state physics.

The phenomenon of catalysis is found in many homogeneous and heterogeneous systems undergoing chemical change, where it effects the rates of approach to the equilibrium state in processes as diverse as those found in the stars, the earth's mantle, living organisms, and the various chemistries utilized by industry. The economies and the living standards of both developed and developing countries depend to varying degrees upon the efficacy of their chemical industries. Con sequently, this century has seen a wide exploration and expansion of catalytic chemistry together with an intensive investigation of specific, essential processes like those contributing to life-supporting agricultures. Prime among the latter must surely be the "fixation" of atmospheric nitrogen by catalytic hydrogenation to anhydrous ammonia, still the preferred synthetic precursor of the nitrogenous components of fertilizers. In each decade contemporary concepts and techniques have been used to further the understanding, as yet incomplete, of the catalyst, the adsorbates, the surface reactions, and the technology of large-scale operation. The contributors to the present volume review the state of the art, the science, and the technology; they reveal existing lacunae, and suggest ways forward. Around the turn of the century, Sabatier's school was extending the descriptive catalytic chemistry of hydrogenation by metals to include almost all types of multiple bond. The triple bond of dinitrogen, which continued to be more resistant than the somewhat similar bonds in carbon monoxide and ethyne, defied their efforts.

The physical properties of water and steam have been the subject of lhorough investigation for a long time. It can, on the one hand, be due to the important role of this substance in the processes that take place in nature and, on the .other hand, due to its wide industrial use. Steam is the most important working substance used in conventional and nuc lear power plants, in chemical engineering and other fields of industry. The variety of practical use of water and steam generates a need for knowing their thermodynamic, transport, electrical, and other properties over a .very wide range of temperatures and pressures. International Conferences on the Properties of Steam, which have taken place since 1929, have the aim to promote wide exchange of the results of theoretical and experimental studies into the properties of ordinary and heavy water in a11 phase states. In the course of last decade f.he investigation oC physical and chemical properties of concentrated and dilute aqueous solutions that are of interest in the first place from the point of view of power play an important part in these studies."

Lead-based paint has become a national issue and will continue to be a hi- priority focus ofnational, state, and local agencies until there is no lead-based paint in the United States. Lead-based paint has become a tremendous health hazard for people and animals. Lead-based paint has been in widespread use throughout Europe and the United States. Lead has been known to be a health hazard since the time ofPliny the Elder (A. D. 23-79), but it was deemed that the advantages of lead in paint outweighed the health hazards. There has been a change in outlook, and in 1973 the U. S. Congress banned all lead paint from residential structures. A voluminous number of law suits have been initiated since, and continue to be litigated with the purpose of determining the parties responsible for the lead poisoning of children and others and to exact the indemnities. Lead-based paint is still authorized for use on bridges and nonresidential structures, and thousands of city, state, military, and federal government housing projects still contain lead-based paint. This paint must be removed if these dwellings are to be safe living quarters, especially for children. Aba- ment techniques continue to be evaluated; some have been used successfully. Lead-based paint abatement will continue into the next century, and it is hoped that this comprehensive volume will serve as a guide for those seriously interested in this important subject.

aiThis book starts with depiction of the phosphorus role in life creation and evolution. Then it outlines in which vital processes different phosphates participate in life of all flora and fauna, from DNA molecules till body tissues. Crucial function of phosphates was noticed long ago, but only in XIX century discovery of mineral fertilizers made it possible to sustain the needs of growing global population, thus initiating a green revolution. Though, for many decades after it, the complexity of interactions fertilizer-soil-plant roots was underrated, causing massive damages, such as soil destruction and eutrophication of waters. Still, mining of exhausting natural phosphate reserves continued worldwide. Lessons of what happened in XIX century due to scarcity of phosphates were ignored. In the meantime, production of phosphates reached its peak few years ago. Immediate implementation of phosphate recycling technologies from municipal wastes can help avoid imminent global disaster.ai

Metal-Oxygen Clusters is the first book, providing an overview of the surface chemistry and catalytic properties of heteropoly oxometalates. After a brief look at the early knowledge of heteropoly oxometalates, the book discusses the synthesis, characterization, structure, bulk properties and stability of these materials. The remainder and the largest portion of the book explores the properties of these solids as catalysts in acid-catalyzed and oxidation processes in supported or unsupported forms. The book provides an up-to-date review of the methods for synthesizing heteropoly oxometalates of Keggin structure, techniques from spectroscopic through electrochemical to elemental analysis for their characterization and the current information on their structure, bulk properties and their stabilities at high temperatures and under acid and alkaline conditions. The book discusses the materials employed as supports for the title solid and the results of the examination of the supported materials. Methods for the identification of the nature and source of the two catalytic functions, the acidic and oxidative properties, of the heteropoly oxometalates are reviewed and discussed. The use of both the supported and unsupported heteropoly oxometalates as catalysts in acidity-requisite processes ranging from methanol conversion to hydrocarbons to ring-expansion and contraction processes and in oxidation processes from methane cyclohexane are described and related to the aforementioned properties.

To the biochemist, water is, of course, the only solvent worthy of consideration, because natural macromolecules exhibit their remarkable conformational properties only in aqueous media. Probably because of these remarkable properties, biochemists do not tend to regard proteins, nucleotides and polysaccharides as polymers in the way that real polymer scientists regard methyl methacrylate and polyethylene. The laws of polymer statistics hardly apply to native biopolymers. Between these two powerful camps, lies the No-man's land of water soluble synthetic polymers: here, we must also include natural polymers which have been chemically modified. The scientific literature of these compounds is characterized by a large number of patents, which is usually a sign of little basic understanding, of 'know-how' rather than of 'know-why'. Many of the physical properties of such aqueous solutions are intriguing: the polymer may be completely miscible with water, and yet water is a 'poor' solvent, in terms of polymer parlance. ~kiny of the polymers form thermorever sible gels on heating or cooling. The phenomena of exothermic mixing and salting-in are common features of such systems: neither can be fully explained by the available theories. Finally, the eccentric behaviour of polyelectrolytes is well documented. Despite the lack of a sound physico-chemical foundation there is a general awareness of the importance of water soluble vinyl, acrylic, polyether, starch and cellulose derivatives, as witnessed again by ~he vast patent literature.