SOME PROPERTIES OF ICE 115 



" bind " into a snowball. You cannot make snowballs 

 during very hard frost the snow must be in air of 

 a thawing temperature at the moment it is squeezed by 

 the hand. The hand itself will not be warm enough to 

 produce that temperature when the thermometer is 

 below freezing-point. The snow commences to melt in 

 the hand when one squeezes it, and then when the 

 squeezing is stopped the water formed quickly freezes 

 again and cements the snow particles together to 

 form ice, enclosing innumerable minute bubbles. The 

 heat of the sun and the pressure of the weight of 

 the snow itself take the place in the mountains of the 

 warmth and pressure of the human hand. The minute 

 air bubbles make the newest glacier-ice white and 

 opaque, especially when seen in a great mass ; but 

 gradually they get squeezed together, and the glacier 

 ice becomes first " fibrous " in appearance, and then, 

 after long years of pressure by its own weight, fairly 

 clear. Ice in great masses has the properties of a 

 viscous body, like pitch or soft sealing-wax, owing to 

 the fact that wherever the solid mass breaks its particles 

 melt a very little and then freeze again. Under increased 

 pressure ice melts at a lower temperature than when it 

 is not subjected to pressure. When the pressure is 

 removed the water freezes again. Thus crushed ice or 

 snow can be put into a " squeeze-mould " and pressed, 

 so as to form a solid mass of ice of any shape you may 

 choose. Four or five slabs of ice, placed one over the 

 other, very soon become, owing to this property, one 

 continuous solid mass. White glacier ice is so full of air 

 bubbles as to be comparable in structure to sponge, or, 

 more closely, to cork. A cube of such ice exposes, 

 owing to its rough air-hole pitted surface, a much larger 

 surface of contact to the atmosphere than does a cube 

 of perfectly smooth clear ice. Consequently in a warm 

 room or chamber the white ice melts much more quickly 

 than does the clear, and hence you should choose clear 



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