CARBON AND CARBONIC ANHYDRIDE. 83 



crystallized, but differently from what it is in graphite. It 

 is the hardest of all substances. It has not the least resem- 

 blance to coal, yet it can be burned up in oxygen, car- 

 bonic anhydride being the result, as in the burning of coal 

 and other forms of carbon. It was discovered to be carbon 

 in this way by Lavoisier, a French chemist. He threw the 

 sun's rays, concentrated by a large lens, upon a diamond in 

 a vessel of oxygen gas. It was consumed, and carbonic an- 

 hydride alone resulted, showing that the substance that had 

 thus united with the oxygen was nothing but carbon. No 

 one has ever yet been able to convert coal into diamonds. 

 The difficulty seems to be that coal can neither be dissolved 

 nor melted, for, in order to crystallize any substance, it must 

 first be in a liquid state. It is indeed stated that a French- 

 man, M. Despretz, has with a galvanic battery melted and 

 crystallized carbon, and thus made diamonds; but they 

 were so small as to be visible only with a microscope. 



101. Allotropism. You have learned that the elementary 

 body carbon appears under three very different forms dia- 

 mond, graphite, and charcoal varying in color, hardness, 

 specific gravity, and other physical properties. "We can 

 not explain exactly how and why this is so, but we know 

 that some other elements appear in two or more distinct 

 forms, and the peculiarity is not confined to carbon. Bear 

 in mind that, chemically, diamond, graphite, and charcoal 

 are one and the same, but they differ in their physical as- 

 pects. Bodies having this power of taking different forms 

 are said to be allotropic, and the phenomenon is called allo- 

 tropisra. These words are made up from two Greek words, 

 allos," other," and tropos, "way," because the body exists in 

 some "other way." When we say that carbon exists in 

 three allotropic forms, we do not explain any thing; we 

 rather conceal our ignorance of the truth by employing a 

 high-sounding word coined for that purpose. 



