EVAPORATJOX. 



containing a fe\v drops of water, and the pressure of the 

 air upon the surface of the ether be removed by the air- 

 pump, the ether will boil and the water will freeze. The 

 heat which the ether absorbs in boiling causes the water 

 to freeze. From the same cause, wetting the hands with 

 ether will make them severely cold. The ether evapo- 

 rating takes away heat from the hands. 



The fact that liquids are driven oft* or made to boil at 

 lower degrees of heat when the pressure of the atmo- 

 sphere is lessened or removed, has recently been applied 

 to some very useful purposes. 



The process for refining sugar is to dissolve impure 

 sugar in water, and after clarifying the solution to evapo- 

 rate the water that the dry, crystallized mass may remain. 

 Formerly this operation was conducted under atmo- 

 spheric pressure, and a heat of 218 or 220 was requisite 

 to make the syrup boil : by this heat a portion of the 

 sugar was often discolored and spoiled, and often the 

 whole was more.or less injured. The thought occurred 

 to Mr Howard that this evil would be remedied, if the 

 water were dissipated by boiling in a place from which air 

 was excluded, as the temperature then required would be 

 so low as not to injure the sugar. The plan proposed by 

 him was tried and succeeded ; and the saving of sugar 

 and the improvement of quality were so great as to make 

 the patent right, by which the emoluments of the process 

 were secured to him and others, worth several thousand 

 pounds a year. The syrup, during this process, is not 

 more heated than it would be in a vessel merely exposed 

 to a summer sun. This is an interesting instance of 

 the application of philosophical principles to purposes of 

 practical utility. 



The process of distillation affords another instance. 

 This process consists simply in bringing the more volatile 

 parts of any substance by means of heat into an aeriform 

 state, and then condensing them again in appropriate ves- 

 sels. Many substances which are changed and injured 

 by high degrees of heat, may be obtained of very superior 

 quality by carrying on the operation in a vacuum. The 

 essential oils of lavender, peppermint, &c, never had the 

 natural flavor and virtues of the plants themselves, until 



