JOURNAL OF CHEMICAL EDUCATION
THE CONTENT OF A COURSE IN COLLOID CHEMISTRY J. L. SHERESHEFSKY ~ o w a r dUniversity, Washington, D. C.
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colloid chemistry courses offered in our colleges such minor aspects as time, credit hours, and whether and universities, unlike introductory courses in other laboratory work is integrated or separate. But there fields of chemistry, differ from each other in many are also evident differences in purpose, level, and conrespects. This becomes immediately evident upon tent., reading the descriptions of these courses in the bulletins In most institutions the subject of colloid chemistry and catalogs of the representative schools. There are is framed into a course of one semester, two hours a considerable differences to he noted with respect to week, or the equivalent of one term, three hours a week,
JANUARY, 1949
devoted to lecture or discussion. Next in frequency are the schools in which the courses are given in one semester, three hours a week, or the approximately equivalent of two quarters, two hours a week. There are only a few institutions in which the subject of colloid chemistry merits a full year's work, either in two semesters, or three quarters, two hours a week. In a few instances, in addition to the introductory course there are offered separate courses in more specialized branches of colloid chemistry. The laboratory courses are usually flexible, allowing for variation in the extent of practical work. This practice is presumably due to the heterogeneity of the student group attracted to these courses and aims to serve the needs of the individual student. However, the instances in which laboratory work is either integrated with the course or given separately are very few indeed. It would seem that instmction in colloid chemistry in the American colleges and universities is mainly in the form of lectures, discussions, and seminars. Greater uniformity is to be observed in the required preparation of the students admitted to these courses. Only in one or two instances, where the courses were specifically for undergraduate or premedical students, were the prerequisites limited to two and a half or three years of chemistry. Most institutions, however, emnhasize that the courses are for the advanced undergraduate or graduate student or both, and in general require as prerequisites the equivalent of four years of chemistry including physical, a t least one year of physics, and mathematics through calculus. With respect to content and level of instruction there are two distinct types of courses, differing mainly in the emuhasis placed on the study of boundary phenomena and related subjects. The courses as given in most schools are in general limited to a survey of the properties of lyophobic and lyophilic systems and their application to industry, or biology and medicine. The topics commonly included in these courses are: methods of preparation; osmotic properties; optical properties; electrical properties; stability; lyophobic colloids; lyophilic colloids; emulsions; gels; smokes and dusts. Boundary conditions are treated on an elementary level, mostly on a qualita+ive basis and to the extent required in the explanations of the behavior of the colloidal phenomenon under consideration. It is rather remarkable that such basic phenomena as surface tension, electrical properties of surfaces, and adsorption-which are generally the standard foundations of the science, are treated on a level not higher than accorded them in an elementary treatise on physical chemistry. The other type of colloid chemistry course is not very common. It is being given in relatively few institutions. It d i e m from the type just discussed in that it emphasizes the treatment of the boundary phenomena as the foundation for the understanding of the behavior of .colloid systems. This type of course treats, in general, the same topics
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as enumerated above, but only after an extensive study of surface and interfacial phenomena. The writer of these remarks has given this type of course for a number of years a t irregular intervals. The topics discussed in this course include the following: I. The Liquid-Gas Surface Surface tension phenomenon Theories of surfsce tension Methods of measuring surface tension Surface tension of pure liquids Surface tension and temperature Total surface energy Surface tension and vapor The capillary phase 11. The Solution-Gas Surface Types of surface tension-concentration curves Surface tension of aqueous solutions of salts, acids, and bases Surface tension of aqueous solutions of organic compounds Surface tension of solutions in organic solvents Theories of surfsce tension of solutions Adsorotion at the surfaces of solutions ~ t r u c t h of e the oapillarylayer Equation of state of soluble films 111. The Liquid-Liquid Interface Interfacial Tension effect: chemiMethods of measurement:. temoerrtture . cal co~stitution;adhesionand cohesion; spreading Interfacid tension of solutions Adsorption Method of measuring; adsorption isotherm I V. The Solid-Gas Surface The nature of solid surfaces Surface energy of solids Adsorption General; heat of absorption; theories of adsorption; methods of measuring; particle size determination Contact catdysis V. The Solid-Liquid Interface Interfacial tension Direct method; solubility method Displacement of liquids Wetting; contact angle; applications Adsorption from solutions Methods of measuring; theories of adsorption; dilute and coneentratedsolutions Adsorption of ions LVotropic series; preferential adsorption; ion exchange Adsorption analysis Method; theory; applications VI. Monomoleculsr Films Spreading and orientation Types of films Methods of measurements Structure of molecules in films Films on solid surfaces VII. Electrical Properties of Surfaces Electrical nature of surfaces Electrical double layer; contact potentials Surfsoe tension and electrical polarization Eleotrokinetic phenomena Electrophoresis; electro-osmosis; streaming potentials; sedimentationpotentials VIII. Physics and Chemistry of Colloids Colloidd systems
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JOURNAL OF CHEMICAL EDUCATION Dispersion; aggregation; colloidal dimensions; the colloidalstate; typosof colloidalsystems Suspensoids Preparation; physicalproperties; opticalproperties; eleetricalproperties; purification Stability and coagulation Emulsions Emulsifyingrtgents; theories; types; hreakingemulsions: foams Emulsoids Physical properties; electrical properties; stability; osmotic ~henomena: rote in sols Gels Classification; optical properties; swelling; syneresis; thixotropy; Liesegang phenomenon Aerosols Clouds, dusts and smokes; physical, optical and elwtricalproperties; stability sndprecipitation
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IX. High Polymers
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This course was designed primarily for students of chemistry who have adequate preparation in organic and uhvsical chemistry, physics, and mathematics. ~ecause-ofthe high preGq&kes, only advanced undergraduates or graduate students are admitted to this course. The course also stresses the a~olicationof physical chemistry, i. e., the kinetic and th&odynamic methods in the elucidation of colloidal systems. Colloid chemistry is here regarded not as a chapter in physical chemis-. try, but rather as a broad field of knowledge with many facets and ramifications upon which the proved methods of theoretical chemistry can be profitably applied.
