Abstract
According to Freundlich, 1 when a sol containing rods, discs, or leaf-shaped colloidal particles is flowing through a tube the particles become oriented with the longest axis of the particles parallel to the direction of flow. Discs or leaf-shaped particles near the walls of the tubes also tend to be oriented with their faces parallel to the adjacent wall. Ambronn and Frey 2 reported that sols containing rod-shaped particles are doubly refractive when the particles are oriented by streaming and the direction of observation is perpendicular to the direction of flow. Sols containing discs or leaf-shaped particles show double refraction when the longest axis of the particles is parallel to the direction of flow and the faces of the particles are parallel to the direction of observation.
The above phenomena led us to assume that if a sol containing rod-shaped particles were forced from a small glass tube of circular cross section into the same sol contained in a beaker the orientation of the particles should be the same throughout the stream and all parts of the stream should, therefore, show double refraction. If the direction of flow were reversed and the sol were sucked from the beaker through the small glass tube the sol in the beaker should flow radially toward the mouth of the tube as a center and the long axis of the particles should be oriented parallel to the directions of flow. All regions of the sol in the beaker which are flowing toward the mouth of the tube would be expected to show double refraction except those regions which are flowing parallel to the vibration directions of the crossed nicols. A dark cross should, therefore, be observed in the doubly refractive sol which is flowing toward the mouth of the tube.
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