62 A YEAR IN SCIENCE 



with impurities and furnish a hotbed for whatever 

 germs may find their way there. So, instead of remov- 

 ing the things that are injurious, it may be the means 

 of supplying them. The necessity of keeping the filter 

 thoroughly cleaned must be clear to all. 



Charcoal is also used as a decolorizer. For this 

 purpose, however, animal .charcoal is chiefly used. If 

 you have ever visited a sugar beet factory, no doubt 

 you were impressed by the difference of color in the 

 dark sap from which the sugar is made and the beaft- 

 tiful white crystals of commercial sugar. This trans- 

 formation in color is brought about in the large filters, 

 called charfilters, which contain this finely divided 

 charcoal through which the syrup passes. Large quan- 

 tities of charcoal are used in sugar refining. 



Lampblack. Lampblack or soot is practically pure 

 carbon. It is obtained by incomplete burning; that is, 

 by burning with a limited supply of air. This can 

 be shown by cutting off the air to your Bunsen flame 

 and holding a white porcelain plate over the flame. 

 The soot will collect on the plate. This finely divided 

 black powder furnishes the pigment for the manufac- 

 ture of printer's ink and paint. 



Coal. Generally speaking, coal is divided into soft, 

 or bituminous, and hard, or anthracite coal. The dif- 

 ference is greater than the mere physical difference of 

 degrees of hardness and is explained by the greater 

 percentage of carbon found in the hard coal. Anthra- 



