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Two studies of creeping have been recorded. E. R. Washburn (4) tried various solutions and solid surfaces and noted the general nature of the phenomenon. He observed that creeping is found not only in aqueous solutions of electrolytes, but also in non-aqueous solutions (e.g, sulfur in carbon bisulfide), and occurs not only on glass, but also on porcelain and metals. J. G. F. Druce (1), in common with Washburn, found quantitative results practically impossible because of the large number of variables, but submitted a list of substances "in descending order of creeping:" ammonium chloride, zinc sulfate, barium chloride, potassium nitrate, manganous sulfate, sodium chloride. Druce does not describe his experiments.Washburn seems to have worked with solutions evaporating in dishes. The latter offers as an explanation of the phenomenon the formation of capillaries by the deposited crystals, up which the solution may rise with the subsequent deposition of more crystals and the formation of new capillaries. It is difficult to picture how the capillaries are formed originally, for the protrusion of the crystals beyond the limits of the solution seems much like raising oneself by one's bootstraps. The present authors find that creeping does not start by the formation of capillaries, although these undoubtedly contribute largely to the maintenance of vertical creeping.The prime factor in the production of creeping is the ability of the solid solute to wet preferentially the solid surface over which the creeping takes place. EXPERIMENTSTo obtain a quantitative estimate of the height to which a creeping solution will climb, glass rods, thoroughly washed and repeatedly rinsed with distilled water, were suspended with the lower end of each rod under the surface of a saturated solution of either ammonium chloride, potassium chloride, sodium chloride, or potassium iodide. The apparatus was placed under a bell jar to insure as far as possible uniform conditions of evaporation. Concentrated sulfuric acid served as a drying agent. Table 1 shows the numerical results obtained.In agreement with the results of Druce, ammonium chloride is the "best" 439

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