The Creeping of Saturated Salt Solutions.

Abstract

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

Formation and development of salt crusts on soil surfaces

“…The effect of the substrate hydrophobicity or hydrophilicity on the topological character of precipitates has been observed in other salts such as K 2 Cr 2 O 7 [34], ammonium chloride [13], potassium nitrate, potassium chloride, and ammonium chloride [13,38]. …”

“…The pioneering work on salt creeping along glass walls concluded that capillarity draws solution upward to the growth front through tiny spaces among crystallites or between the crystallites and the glass wall [37]. It is later suggested that the solution is transported over rather than under the crystallites, given the limited space between the growing crystals and the glass wall [13]. Yet, a recent study using a high-magnification microscope reveals that K 2 Cr 2 O 7 crystal growth is largely determined by the solution transport between the crystallites and the substrate [34].…”

Droplets of Ionic Solutions

“…. A more thorough scientific study was later performed by Hazlehurst et al (1936), who challenged Washburn's proposed mechanism: "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 ones bootstraps . in much the same manner that it would have done if the bottom of the dish had been cracked."…”

Migration of sodium chloride in dry porous materials

“…If an initially dry solid is stood in a shallow tray of concentrated brine, salt will eventually begin to migrate up the side of the object, first as a translucent layer of fine crystals and later forming an outer skin of crystals in the form of dendritic outgrowths. This phenomenon was initially referred to as creep [7,8] but here it will be termed autogenous wicking. The process begins with evaporation causing the brine solution to become supersaturated, followed by the nucleation of crystals at the brine meniscus.…”