LESSONS IN CHEMISTRY. 129 



The absorbing properties of charcoal make it a good deodor- 

 izer and a powerful disinfectant, and it is much used in making 

 water filters. Charcoal from bones is much used in sugar refin- 

 eries to decolorize sirups. It destroys bad odors, and discharges 

 colors, not only by absorbing gases, but the absorbed oxygen 

 acting chemically on the noxious gases and other substances 

 changes them to harmless compounds. 



Soot is another form of nearly pure carbon. It is carbon which 

 has been released by heat from its combinations, without being 

 burned, it helps to form the smoke of combustion. It may be 

 condensed from the smoke as a fine black powder. It is used for 

 making printers' ink, black paint, etc. .In the distillation of coal 

 for the manufacture of illuminating gas, there is deposited on the 

 inside of the retort a grayish coating called gas carbon. It is 

 quite as nearly pure carbon as any of the other forms, but 

 whether it is a variety of graphite, or a fourth form is not 

 settled. Gas carbon is a good conductor of electricity, and is. 

 used for electric-lamp carbons and other purposes. Coke and an- 

 thracite coal are nearly pure carbon. The different kinds of soft 

 coal and peat all have carbon as the basis of their composition 

 but associated with various impurities. 



All these forms of carbon seem to be the result of the slow 

 decomposition of organic matter, mainly vegetation, usually 

 under water, so that the supply of oxygen was limited. This 

 mass of decomposing matter covered with sand or clay, sub- 

 jected to pressure and heat, gradually changed into various kinds 

 of coal and graphite. It seems hardly possible that the black, 

 brittle, porous charcoal, and the soft compact graphite are chem- 

 ically identical with the beautiful diamond. They are specimens 

 of the same element appearing in different or allotropic forms, 

 and notwithstanding their marked differences, they have well- 

 marked properties in common. The explanation of these differ- 

 ent forms of carbon is one of the unsolved problems of chemistry. 



Carbon combines freely with oxygen in all forms of combus- 

 tion and combines also with hydrogen, nitrogen and other ele- 

 ments. When any of the forms of carbon is burned in oxygen 



t S.-9 



