THE PHYSICS OF ICE. 399 



THE PHYSICS OF ICE. 



By E. lewis, Jr. 



THREE-QUARTERS of a century ago a cargo of ice was obtained 

 from a pond near the junction of Broadway and Canal Street, 

 in New York, and sent to Charleston, South Carolina, in a vessel 

 chartered by a gentleman of that city. But it was in 1805-'6 that 

 Frederick Tudor, of Boston, inaugurated and laid the foundation of 

 the now immense ice-trade of the United States by shipping, as a mer- 

 cantile adventure, a cargo to St. Pierre, on the island of Martinique. 

 This cargo, with several subsequent shipments to other West Indian 

 ports, was largely unprofitable. The people to whom it was sent, un- 

 familiar with its use, knew little of its value. 



In 1833, Mr. Tudor sent in the ship Tuscany the first cargo of 

 ice from this country to Calcutta, and thus began the ice-trade of 

 the United States with seaports of India. Several years after that 

 event, the Hon. Edward Everett, then our minister to England, met 

 in London a wealthy and eminent Hindoo, who cordially thanked 

 the American people whom he represented for the great service they 

 had done to his countrymen in shipping cargoes of ice to India. It 

 is obvious that, in our zone of alternate heat and cold, ice is one of 

 Winter's great benefactions. In the healthy preservation of food it 

 is indispensable during summer's heat. In regions where little ice 

 forms, the mountain-snows are economized. Some years since the sup- 

 ply on Mount Etna gave out, and a glacier buried beneath sand and 

 lava was found, and worked as an ice-quarry to supply the necessities 

 of the people. Ice of good quality is now produced by artificial meth- 

 ods, but it is our purpose to develop in this paper some of the physical 

 properties and phenomena of ice, rather than its economic value. 



Ice is simply water in a solid state. In ordinary conditions it be- 

 gins to form at a temperature of 32° of Fahrenheit's thermometer, and 

 this is the well-known freezing-point. Below it the molecules of water 

 become fixed in the grasp of molecular force ; above it they are sepa- 

 rated by heat, and fall asunder, forming liquid water. But to this 

 law are exceptions, in which water may be cooled many degrees be- 

 low 32°, still remaining liquid. In glass vessels exposed in open air, 

 water kept perfectly still has been reduced in temperature 15° be- 

 low freezing, and in a vacuum much lower than this. In this con- 

 dition there is a " tendency to freeze which is kept in check only by 

 the difficulty of making a commencement," and the process begins by 

 the slightest jar of the water. Fine particles of vapor, or mist, and 

 water in fine capillary tubes, may remain unfrozen 20° or more be- 

 low the freezing-point. Water thus cooled rises in temperature the 

 instant crystallization begins, by liberation of its heat, and at 32° 



