24 ROYAL SOCILTY OF CANADA 



differently from their contents. An explanation is given of the well- 

 known appearance of *' glacier grains/' which are supposed to be foam- 

 cells filled with pure or nearly pure ice, and separated from one another 

 by visible or invisible walls of oily salt solution. 



The phenomenon of regelation is explained as the running together 

 of two gelatinous clots, containing liquid foam-cells and liquid cell- 

 contents. Similar effects have been obtained with silicic acid or glue. 

 In the formation of ice we have to do with the separation of pure ice- 

 crystals and mother liquor rich in the dissolved salt, which is always 

 present to a greater or less extent in the water. Since a surface tension 

 exists at the boundary of separation, invisible foam-walls are formed. 

 As the freezing proceeds, the mother liquor continually becomes more 

 concentrated and the foam-walls thinner. Finally, the mother liquor 

 also freezes to ice and solid salt. Air in the water, like the dissolved 

 salts, separates out at short intervals and gives rise to the white places 

 in ice. The air accumulates at the places rich in salt solution. Since 

 the foam-walls, or parts richest in salt, possess a lower melting-point than 

 pure ice, these melt first when an ice-block is subjected to the action of 

 sunlight, or any radiant heat-energy, and give rise to the beautiful lique- 

 faction figures of Tyndall. Artificial ice is seen to be traversed by many 

 horizontal tubes, normal to the surface, which are especially numerous 

 in the diagonal and median planes of the ice-block where the mother 

 liquor had accumulated. 



The small spherical bubbles which are often noticed in an ice-block 

 subjected to melting are tubes of melted salt solution which have broken 

 up with contraction of volume ; these may be vacuous or full of air. Some 

 judgment can be made on the velocity of freezing, for the more rapidly 

 water solidifies the more numerous are the foam-cells. By repeated frac- 

 tional freezing and melting of the ice-crystals formed, the author suc- 

 ceeded in obtaining purer and purer ice with increasingly large foam- 

 cells or glacier grains. He states, however, that he has not succeeded in 

 obtaining, by this means, ice free from foam-walls or from glacier grains. 



A study of separate glacier grains in artificial ice shows that it con- 

 tains differently orientated crystals of ice, whose optic axes are very sel- 

 dom normal to the surface. 



Wlien in natural ice the optic axis of the separate crystals in the 

 different grains is found to be normal or parallel to the free surface of 

 the water, the separation of orientated crystals of ice may have been 

 started by the contact action of ice-crystals or snowflakes falling on the 

 surface of the supercooled water, and swimming thereon in a horizontal 

 position. 



