54 GENERAL SCIENCE 



It is also widely used as a filter for purification of air, 

 water, sugar, vinegar, etc. 



Sewer gases, which have a bad odor and are sometimes 

 poisonous, can be prevented from escaping to the streets 

 and buildings by the use of charcoal filters at the sewer 

 exits. As charcoal is very porous, it absorbs the poisons 

 of the gases and thus keeps the regions surrounding 

 sewers clean and free from bad odors. Pieces of charcoal 

 placed in flower vases will prevent discoloration of the 

 water and absorb the odorous gases of the stems that 

 may be decaying. Charcoal filters used to purify drink- 

 ing water may become dangerous, as the pores of the 

 charcoal may become filled with impurities, and thus as 

 more water flows through, it may become contaminated 

 instead of purified. Such filters should be changed or 

 cleaned often. It is very difficult to wash the filth out 

 of the filter unless the charcoal is in powdered form. 

 The charcoal may be purified by heating it to redness. 

 This will oxidize all the dangerous material collected in 

 the pores. 



Sugar is made of the sap from the sugar maple tree 

 and of the juice from the sugar cane and the sugar beet. 

 The raw liquids from these plants are boiled down, that 

 is, the water is made to evaporate, and the sugar is allowed 

 to crystallize. This is known as raw sugar; it has a 

 brown color and usually an unpleasant taste. This raw 

 sugar is sent to the sugar refinery, where it is heated and 

 again turned into a sirup. The sirup is filtered through 

 charcoal known as bone black or animal charcoal. From 

 this filtered sirup the white, clean sugars on the market 

 are made. The charcoal made from animals has a greater 

 refining power than that made from wood, and for 

 this reason it is used in the sugar industry. 



