The Diffraction of X-rays in Organic Mixtures

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Abstract
An examination was made by an x-ray diffraction ionization method of the following mixtures: ethyl alcohol-methylcyclohexane, butyl alcohol-ortho-dimethylcyclohexane, quinoline-phenol, paraldehyde-cyclohexane, tetranitromethane-cyclohexane, and phenol-water. All of these mixtures are totally miscible, except the last, phenol-water, which is totally miscible at higher temperatures and is an emulsion in some proportions at ordinary temperatures. In all cases of solutions the diffraction exhibits a single major peak which has an angular position between the positions of the peaks of the constituents and shifts directly with the concentration but in general not in a linear manner. There is in some cases definite indication of the existence of secondary peaks corresponding to those found in the pure constituents but these also shift. In the single case examined of an emulsion, the major peaks of both constituents were found and the intensity of each varied directly with the concentration of that constitutent. The results indicate that in a solution there exists a single type of cybotactic group and that the molecules of both constituents enter this formation. The length of the most probable space periodicity in the group depends upon the proportion of the liquids involved. The emulsion contains two types of cybotactic groups corresponding to the two constituent liquids. These conclusions suggest a very fundamental differentiation between solutions and nonsolutions. This differentiation between solutions and nonsolutions does not depend upon the fineness of the separation of either liquid. A solution exists when and only when the components, instead of having their individual space molecular groupings, conspire to form a single type of cybotactic group. With this description, the nature of a solution has a similarity to that of a crystal and has a definite concept.