CHAP, iv.] APPLICATIONS OF THE LAWS OF HEAT. 



37' 



apparatus called the coil, because it is twisted in a helix. The vapour 

 produced by boiling rising above the water in the cucurbit, is carried 

 to the coil and there condenses by contact with the sides, which are 

 kept constantly cool by a vessel of water in which the coil is plunged. 

 The distilled water is collected outside this vessel in a bottle, g. The 

 constant condensation of the vapour can only take place by the ex- 

 change of the heat of vaporization with the water in the vessel e, and 

 its consequent elevation of temperature. The cold water must there- 

 fore be renewed as fast as the distillation is effected, and this is done 

 by means of a tap K, which brings the cold water to the bottom of 

 the vessel through the funnel li and tube d, while the warm water 

 runs away from the top by the pipe i. 



FIG. 259. The alembic, a distilling apparatus. 



The alembic is employed on shipboard for distilling sea water, and 

 is able to a certain degree to supply fresh water for the requirements 

 of the crew. Water distilled in this way is worth about a halfpenny 

 a gallon. 



A distilling apparatus is more complicated when we have to deal 

 with a mixture of liquids unequally volatile, such as alcoholic liquids. 

 With an ordinary alembic indeed, and several successive distillations, 

 we can obtain the concentrated liquid sought for to a certain degree of 

 purity, but in this case the liquid, as alcohol for example, always has 

 a burnt flavour, and this must be destroyed.. 



