No. 144.] 383 



zero. A mass of ice formed in the way alluded to would mea- 

 sure in a rough way, by its depth, the severity of the winter in 

 which it was formed. The gentleman who devised this plan suc- 

 ceeded in making only about five or six feet in depth. If he had 

 been sufficiently diligent, the mass would at no time have /alien 

 in temperature below 32^. As it was, it may be presumed to 

 have remained at about that point, for with the commencement 

 of warm weather it began to melt. The difficulty with this plan 

 is that it does not expose a sufficient amount of surface. By the 

 common process we gather together and pack down in a small 

 cubic space the cold from the surface of an acre or so of exposure. 

 This cold is reproduced for culinary or other purposes when the 

 ice melts. 



When ice is stored the sum of its useful properties is its latent 

 cold (140», by the absorption of which water at 32° becomes ice 

 of the same temperature), added to its sensible depression of tem- 

 perature below the freezing point, i. e., towards zero. Ice put up 

 in severe weather is worth more and keeps better than that put 

 up in thawing weather, because it is colder. If the ice house be 

 large and the ice be put in at a temperature near zero, it is said 

 to obviate the necessity of drainage, ice at zero being to ice at 32° 

 in value as 172 is to 140. The surplus sensible cold being suffi- 

 cient to neutralize the rise in temperature of the mass during the 



But the depth of ice that may be formed in this way, is two or 

 three times the thickness of the ice that forms on the surface of 

 ponds. As soon as a sheet is formed over water, it protects the 

 water to some extent from the cold. The more completely a lake 

 is kept skimmed of ice during the ice producing season, the 

 greater is the quantity of the crop, though it is of a poorer quali- 

 ty. The successive formations are thinner and more disposed to 

 thaw. Our annual ice formation measures by its thickness the 

 severity of the winter, and its production absorbs and renders la- 

 tent just as much cold (140°) as the same amount of water in 

 freezing gives out heat. Nothing will freeze in a cellar where 

 there is open still water until some time after the water is coated 

 with ice. A tub of water may in this way be made to exert a 



