Little scientific work has been done on the dispersion of powders in organic media, in spite of their industrial importance in such fields as paints and lacquers. Harkins and coworkers (4) have studied the dispersion of metallic oxides in organic media. Rehbinder and coworkers (5) have studied the dispersion of metallic oxides, chromates, and other powders. A study of carbon dispersed in xylene has been made by Damerell and L'rbanic (2).The purpose of this investigation was to study the effect of various surfaceactive agents upon dispersions of calcium carbonate in xylene. The method of study was similar to that used with carbon-xylene systems, reported in an earlier paper (2), and for greater detail in the explanation of experimental work the reader is referred to that paper. Calcium carbonate was chosen as the disperse phase because of its availability in aggregated colloidal form, its purity, its relatively low specific gravity, and its polar nature, which contrasted with the nonpolar material previously studied.The systems were made by stirring very finely divided calcium carbonate with xylene in the presence of surface-active agents. The degree of dispersion was measured by a combination of sedimentation and ultramicroscopio analysis. The effect of heat, cold, extreme dryness, and the addition of other liquids was studied also; in addition, cataphoresis experiments were carried out and the surface area of the dispersed phase was measured. CHEMICALS SUMMARY 1. Dispersions of calcium carbonate in xylene have been made in the presence of a number of surface-active agents.
Although several micro methods for the determination of surface ten-sion1 and density2 are known, none of the apparatus employed in these is applicable to both determinations. The purpose of this article is the description of an exceedingly simple apparatus by which surface tension and density can be determined on amounts of liquid as low as one-tenth of a cubic centimeter, with a theoretical accuracy of from one part in 100 to one part in 300, depending on the liquid.Apparatus.-A ten centimeter portion of 5 mm. soft glass tubing was heated to softness in a Bunsen burner with wing top attachment and quickly pulled to arm's length. By running a three centimeter column of water up and down the resulting capillary, an eight centimeter portion that had practically uniform bore was found, and a ten centimeter length was cut out so that the eight centimeter portion was on one end. This 1 (a) Du Noüy,
A familiar experiment in colloid chemistry is the formation of insoluble silicate growths, brought about by dropping crystals of various metal chlorides into diluted water glass. These systems are commonly called "Colloidal Gardens" because the silicates form as tubes which superficially resemble growing plants.
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