[BARNES] THE PHYSICAL CONSTANTS OF ICE 23 



bright metallic lustre. It was found that these petals were composed of 

 water. Tyndall found that the relation between the planes of these 

 flowers and the planes of freezing were perfectly constant. They were 

 always parallel to each other. Further, it was found that the develop- 

 ment of these flowers was independent of the direction in which the 

 beam traversed the ice. Hence the direction of freezing could always 

 be told in an irregular-shaped mass of ice by sending a sunbeam 

 througii it. 



A mass of ice may be thus shown to be crj'-stalline in structure, and 

 to be entirely analogous to crystalline solids formed from a saturated 

 solution. The work of Sir David Brewster long ago proved it to be 

 uniaxial, the axis being perpendicular to the surface of freezing. 



Quincke's Theory of Ice Formation. — Eor a great many years Pro- 

 fessor G. Quincke, of the TJniversit}^ of Heidelberg, has made a study of 

 colloidal mixtures of silicic acid, glue, etc., evaporated to form gela- 

 tinous masses, or thin films and develop fissures. He has shown that 

 these viscous oily films of more concentrated solution exist in a less con- 

 centrated solution of the same substance, and form folds, straight and 

 twisted tubes, cylinders or cones, spheres and bubbles, open and closed 

 foam-cells with visible and invisible foam-walls. Thin solid films were 

 shown to behave like films of very viscous liquid. Depending on the 

 viscosity of the oily liquid, the oily films form tubes or bubbles and foam- 

 cells joining on to one another. The mutual inclination of the foam- 

 walls and their surface tensions was shown to continually change as the 

 concentration of the oily liquid changes, and in the case of invisible 

 foam- walls may depend also on the thickness of the oily film. When the 

 oily film is very thin, its surface tension diminishes with diminishing 

 thickness of the film. 



On examining pure-water ice, and ice frozen from water containing 

 added quantities of dissolved salt, melting in the dark, in open air and 

 in sunlight, the author has observed precisely the same group of pheno- 

 ]nena which he met Avith in his study of gelatinous mixtures. For this 

 reason he suggests a theory of ice formation based on his previous know- 

 ledge. Ice is treated as a liquid jelly, with foam-walls of concentrated 

 oily salt solution, which enclose foam-cells containing viscous, doubly 

 refracting, pure or nearly pure water, the terms being used strictly as 

 given above. 



The further the temperature of the ice falls below 0° Cent., the 

 greater the viscosity of the liquid in the walls, and in the interior of the 

 foam-cells. This is shown by the plasticity becoming less. The break- 

 ing of the ice with conchoidal fracture at very low temperatures, occurs 

 at the surface of the invisible spherical foam-walls which have contracted 



