88 GENERAL SCIENCE 



When salts or other substances are in the water, the 

 pure water can be separated from them by distillation, 

 because the molecules of salt are too heavy to escape 

 from the liquid with the vapor. "Hard" water, there- 

 fore, can be "softened" by distillation. Water for the 

 manufacture of ice is also distilled. Large ocean vessels 

 get pure drinking water for the passengers by distilling 

 the salt water of the sea instead of by carrying a sufficient 

 supply of drinking water from the port. 



The commercial uses of distillation are very extensive. 

 The sap of the long-leaf pine trees is collected in barrels 

 and taken to a distillery for the manufacture of turpentine 

 and rosin. When heat is applied the turpentine evapo- 

 rates rapidly and comes out as the distilled product. 

 The rosin, which is a residue of distillation, is left in the 

 boiler, from which it is taken for the market. 



In Chapter IV we learned that alcohol is a waste prod- 

 uct of the yeast plant. Yeast cannot raise the quantity 

 of alcohol in a liquid to more than 14 per cent. In order 

 to get a high percentage of alcohol the process of distilla- 

 tion is used. The fermented fruit juices or fermented 

 grains, such as corn or rye ground up and mixed with 

 water and yeast, are distilled. Since pure alcohol boils 

 at 78 C., it will evaporate much faster than water at 

 78 C., and so the vapor that comes from the fermented 

 juices may contain from 40 to 60 per cent of alcohol, 

 according to the per cent of alcohol in the fermented 

 juice. This distilled product, containing from 40 to 60 

 per cent of alcohol, can be distilled again. The third 

 time that it is distilled, almost pure alcohol is obtained. 

 To this distilled product, containing 80 to 90 per cent 

 of alcohol, quicklime is added. The lime unites with 

 the water which is present in the mixture, but it does 



