The sedimentation volumes of glass spheres, 5 to 15 microns in diameter, were determined in water and in a series of organic liquids. The sedimentation volumes in the organic liquids are identical with that in water or approach this volume as a minimum, as the system is dried more and more intensively. Flocculation of the particles causes the increase from the minimum value. The presence of water dissolved in the liquid and adsorbed on the particles produces this flocculation. The interfacial tension of the organic liquid against water is indicative of the tendency towards flocculation and the difficulty with which the minimum value may be attained. In some cases the sedimentation volume is proportional to the water content of the organic liquid. and in others the liquid must be nearly saturated before flocculation will take place.HE phenomena of setiiment'ation and agglomeration are of vital importance in many manufacturing processes, particularly to the paint and printing ink industries. Agglomeration of pigment particles affects settling and flonproperties of the paint. as well as such factors as gloss, permeability, and durability of the film. For example, the control of flocculation of dispersion is of utmost importance in the formulation of coating compositions. A high degree of dispersion of pigment particles gives improved flon-and gloss which are desirable in certain enamels. Flocculation of pigment particles which induces false bodying or reduced flow in paints is desirable in flat wall and met,al protective T compositions to permit uniform and complete coverage of the surfaces with one coat. A high degree of dispersion results in a hard cake formation of the pigments on settling, which is difficult to redisperse. On the other hand, flocculated pigments settle to a soft cake which is easily redispersed. It is evident, therefore, that a compromise between the two extremes of flocculation and dispersion must be made in pract,ice to formulate usable compositions.A suspension such as a paint is a complex syst'em consisting of a number of solid and liquid phases, and it is almost impossible to determine the effect of a single substance in the mixture. On the other hand, the behavior of glass spheres
JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. This content downloaded from 128.235.251.160 on Mon, 23 Mar 2015 17:34:52 UTC All use subject to JSTOR Terms and ConditionsFilm Reviews uncontrollable-violence in the cities, whether it be the more passive violence of hunger and despair or the virile violence of police torture, murder, gang warfare, and death squads, tests the very bonds of society. The reality of urban Latin America is that governments no longer monopolize violence but spawn it. Such societies are one step from anarchy. The film convincingly illustrates this social reality. Rodrigo D., like the other films of its genre, suggests that basic societal institutions do not function to the benefit of the majority. The foundations of family and kinship network wobble and erode. The church is not visible nor is its voice audible. Schools seem distant, under siege, unappreciated. So far from daily reality are they that people do not even discuss them, much less attend them. Clearly, the most pervasive governmental institution is the police, whose officers show less interest in keeping order and protecting citizens than in killing children and terrorizing the citizenry. The film subtly questions whether it is possible to eradicate mounting urban problems without first restructuring basic societal institutions.Rodrigo D. lays bare the reality of Latin American urban life that the economic platitudes of foreign aid, International Monetary Fund advice, and grandiose governmental plans ignore. Metaphorically, it captures the collapse of society. Does Latin America as we know it at the end of the twentieth century have a future? Many believe that the hoary institutional structures faithfully preserved by the few who derive benefit from them should not and cannot endure. A remarkable continuity of institutions links Latin America to the past but seems to bar it from a future. In 1980, the Brazilian poet Romano de Sant'Anna ably summed up the views of many of his generation in these few words: "I live in the twentieth century. I'm off to the twenty-first, still the prisoner of the nineteenth." A decade later, Victor Gaviria declared in his film that the prisoner has been condemned to death.
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