HEAT OR CALORIC. 107 



ferred for holding the water. A hemispherical earthen vessel, con- 

 taining three pints of water, was placed by Mr. Leslie over a body of 

 parched oat meal, one foot in diameter, and one inch deep, and the 

 whole of the water was frozen by working the pump. 



By the skilful management of evaporation and radiation, ice is 

 obtained at Benares, in a climate where, in the summer, the ther- 

 mometer is never under 100 n , and is often 1 10. 



Shallow pits or beds are made four or five feet wide, and about 

 four inches deep, separated from one another by narrow borders, and 

 so numerous as to cover an extent of about four acres. These pits 

 are filled with dry straw in the middle of then 1 winter, when the ther- 

 mometer is about 40 of Fahr. On the straw are placed rows of 

 shallow earthen pans containing a few inches of water introduced at 

 evening. In the morning they find a little ice, which at sun rise is 

 wrapped in flannel and carried to the ice house. Near Calcutta, a 

 similar process is adopted. In the plains, excavations are made 

 about thirty feet square and two feet deep, and covered about a foot 

 deep with dried stalks of Indian corn or sugar cane. Unglazed 

 earthern pans about 1 J inch deep, are filled with soft water which 

 has been boiled, and in the three winter months, some of it is frozen, 

 every night, when the weather is clear. At sun rising it is carried, 

 wrapped in flannel, to the ice house, which is a deep pit, lined with 

 straw and coarse blankets, and covered by a thatched roof the 

 mouth is closed with straw. L. u. K. 



Quicksilver may be frozen by the united influence of evaporation, 

 rarefaction and absorption. If a pear shaped mass of ice containing 

 the metal, be suspended over a large surface of sulphuric acid, and 

 a good exhaustion obtained, it will freeze the quicksilver, which may 

 be kept solid for several hours. L. u. K. 



The freezing of wet clothes exposed to the air when the thermom- 

 eter is not so low as 32, is occasioned by evaporation. 



Plants are often injured by the frost when the thermometer is above 

 freezing ; this is the joint effect of evaporation and radiation. 



Wine coolers are usually made of porous earthern jars unglazed ; 

 they cool the wine by evaporation from the surface ; several of them 

 on a table have an effect on the air around, which is perceptible to 

 the guests. Rooms are cooled by sprinkling water around them, in 

 hot weather. 



In India, drapery is suspended around their dining halls, which are 

 roofed, but open at the sides, and water being dashed on the cur- 

 tains, the evaporation generates cold. 



(/.) Evaporation contributes to health, by imparting moisture to 

 the atmosphere. The driest air contains moisture, which is often 

 condensed upon cold objects, especially if they are good conductors. 



