the future, and some development of the student's reasoning ability. These five-and the most important
of these for the student who does not continue any work in chemistry as well as for the one who does, is the last!
INVERSION OF AN INTERESTING THREE-PHASE EMULSION JOHN M. ANDREAS .Massachusetts Institute of Technology, Cambridge, Massachusetts
I T IS well known that emulsions consist of droplets of one liquid dispersed in a second and that only two differentemulsions are possible between a pair of given liquids. These binary emulsions are customarily classified as either "oil in water" or "water in oil" emulsions regardless of the exact chemical composition of the two liquid phases. In addition to two-phase emulsions, there exist emulsions involving three immiscible liquids. The latter are more complex and less common, but it is not difficult to prepare them in the laboratory. There are
separated from the continuous phase by the other. Since there is this fundamental difference in structure between the two types of three-phase emulsions, it is not surprising to find corresponding differences in their vro~ertiesin cases where an exam~leof each tvDe can be iormed from the same three liquids. An illustration of this can be studied by repeating the following experiment. T h r e e liquids, xylene, methyl alcohol, and a saturated solution of potassium carbonate in water, are shaken together and allowed to reach equilibrium. For purposes of identification, the xylene may be dyed red with oil-soluble "Sudan II1,"and the water can be colored blue by adding a trace of copper sulfate. Equal volumes of each of the three resulting layers are then filtered into an eight-inch test-tube which is sealed to prevent evaporation. This results in the tube shown in Figure 2. It will be found that the manner in which the tube is shaken determines the type of emulsion which is obtained. 1 If the tube is shaken violently, F I G U ~2E from end to end, drops of water and drops of oil will be dispersed in the alcohol layer (Figure 1-A). If the tube is shaken gently, with a swirling motion, an emulsion is produced in which the water is dispersed in the alcohol and the alcohol is dispersed in the oil (Figure 1-1). It is quite easy to obtain the desired emulsion by starting with the quiescent condition and controlling the method of agitation. However, once a particular type of emulsion is formed, i t tends to persist in spite of vigorous efforts to change it to the other type. Both the emulsions will break if they are allowed to stand for a few minutes, but they differ in the mechanism by which the liquids separate.
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nine possible emulsions which may be formed in such systems, and these are represented diagrammatically in Figure 1. Unlike the binary emulsions which differ only by the composition of the dispersed and continuous phases, these emulsions differ in both the relative positions of each of the liquids and in the structure of the emulsion as a whole. In the first three, droplets of two of the liquids are suspended, side by side, in the continuous phase. In the last six, one of the liquids is
