392 FREEZING WATER BY THE AIR-PUMP. 



in five minutes they were all frozen. An ounce of water in a 

 large flat cavity froze in three and a half minutes. 



A flat-bottom porcelain capsule was prepared for an experi- 

 ment on a large scale by sooting it in the following manner: 

 After coating it with soot over a lamp, and allowing it to cool 

 a little, a small quantity of oil of turpentine was carefully 

 poured upon the edge and passed over the entire surface; the 

 vessel was then warmed to drive off the redundant turpentine. 

 The surface was again coated with soot and again with turpen- 

 tine, and this process was repeated a third time ; finally another 

 coating of soot was added, when it was ready for use. Two 

 ounces of water were placed in this capsule under a receiver, 

 and the air-pump worked for one minute. After standing six 

 minutes the surface was frozen. 



This experiment, as well as similar ones, was attended with 

 violent ebullition on the part of the liquid, throwing the water 

 against the sides of the receiver, which was owing to the rapid 

 formation of vapor on the under surface of the liquid. 



