382 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



prepared to give an account of Mr. Thompson's experiments 

 demonstrating the liquefaction of ice by pressure. 



He then proceeded to consider the formation of ice, and to 

 compare it with the crystalization produced by the cooling of 

 iron, and with the crystalization of stones. He had observed 

 the toughness of newly formed ice. Upon examining a cake of 

 ice, it will be found that the upper portion, less than an inch in 

 thickness, which is first formed, is solid, while the remainder of 

 it is full of pores, like houey-comb. This lower portion of the 

 ice is formed of large crystals, which bear a striking resemblance 

 to the crystals of a pig of the Franklinite ore which has been 

 heated and thrown into water. The outer sixteenth of an inch 

 will bear frequent bending, Avhile the remainder of the pig will 

 break at a blow. Shaving off a single inch from the top of a 

 thick cake virtually destroys the strength of that cake of ice. 

 Hence in the spring, after the warm weather or the rain have 

 thawed the upper stratum of ice, it is brittle and easily broken 

 through, even although it may be twelve or fifteen inches thick. 

 The upper crystals run horizontally, giving strength to the ice, 

 while the lower crystals are larger and run perpendicularly. 



Mr. Veeder suggested that the ice upon the surface is more 

 rapidly formed and therefore does not form so perfect a crystal. 

 But after the ice is sufficiently thick to form a coating to the 

 water below, the process is much more slow, and the crystals have 

 time to take their perfect form. It was formerly the practice, in 

 storing ice, to cut off the top, calling it pithy ice. But it is 

 found better to keep it on. 



Mr. Seely said that water is at its greatest density at a tem- 

 perature between 39 deg. and 40 deg. When exposed to a cold 

 atmosphere, the water upon the surface sinks until the whole 

 reaches the temperature of 39 deg. After that the coldest water, 

 being the lightest, remains on the top, and being a slow conduc- 

 tor of heat, there may be a temperature of zero in more than two 

 inches of ice, while half an inch below the ice the temperature 

 of the water may be 33 deg. The first ice is formed rapidly, and 

 there is no perfect crystalization. After that the water cools 

 more gradually, and being kept still, the crystals are larger and 

 assume a definite form. Water freezes in needle-shaped crystals, 

 always crossing each other at the angle of 60 deg. 



Mr. C. W. Smith asked for an explanation of the formation of 

 ground ice. 



