FREEZING WATER BY THE AIR-PUMP 



WITHOUT SULPHURIC ACID OR OTHER DESICCATING AGENT. 



In attempting to freeze water under the air-pump, without 

 the aid of a desiccating agent, the cooling of the water to the 

 point of congelation is prevented by the heat received from the 

 containing vessel. I have lately found that by obviating this 

 difficulty water may be readily frozen by its own evaporation. 



It was first shown by Count Eumford that water does not 

 wet a sooted surface, but forms in globules like quicksilver. 

 Three drops of water were placed in a sooted watch-glass; the 

 spheroidal globule lay on the soot, exposing a large surface for 

 evaporation, at the same time that the water was insulated from 

 any source of heat. Arranged in this manner and placed under 

 an air-pump, two or three minutes were sufficient to freeze the 

 water. The glass was sooted over an oil-lamp with great care;, 

 the experiment fails if the globule of water touches the glass 

 even by a small point. 



In place of the sooted watch-glass make a shallow cavity in 

 the end of a large cork, and over a lamp burn it, sooting it at 

 the same time. By putting three drops of water into the cavity 

 thus prepared, and subjecting it to the action of the air-pump 

 under a pint receiver, the water froze solid in a minute and a 

 half, and in two and three fourths minutes twenty grains of 

 water congealed, though at 73° Fah. when introduced. Under 

 a receiver of three quarts' capacity twenty grains of water 

 froze in four minutes. I could not succeed in freezing the same 

 amount in the sooted watch-glass. 



By placing corks, prepared as above, over a saucer of sul- 

 phuric acid, the same results are obtained more rapidly. I 

 put half a drachm of water, at 65° Fah., in each cavity, and 

 exhausted the receiver till the mercurial gauge reached four 

 tenths of an inch, which was effected in one minute. In a 

 minute and a half the water on one cork began to freeze, and 



