34 



DIGEST OF A LECTURE 



ON 



"CRYSTALLISATION," 



BY 



W. POPPLEWELL BLOXAM, F.C.S., 



DEMONSTRATOR OF CHEMISTRY, ROYAL NAVAL COLLEGE, 

 GREENWICH. 



iWi JANUARY, 1885. 



The crystal, par excellence, both by virtue of its exceedingly 

 common occurrence and its beautiful variety of form is 

 Water Crystal, or Ice, and, indeed, the class name Crystal 

 comes to us from the Greek word (krustallos), meaning 

 clear ice. 



The word Crystal seems always to have been associated 

 with an idea of value and beauty, although doubtless applied 

 indifferently as a general term to many substances (gems, 

 rock-crystal, &c.), exhibiting, by the light of modern 

 chemistry, widely differing properties and composition. 

 Thus, in the Bible (Job xxviii. 17), "The gold and the 

 crystal cannot equal it." 



All matter in the chemist's arrangement falls under one 

 of two heads, and is either Amorphous or Crystalline. 



A good instance of an Amorphous substance is a 

 piece of clay, whose properties we will consider. It possesses 

 no fixed definite form, may be cut with equal difficulty in all 

 directions, is opaque to light, conducts heat equally badly 

 in any direction through its mass, and cannot certainly be 

 accused of possessing any brilliancy or lustre whatever. It 

 is, in fact, shapeless or amorphous, i.e., not built up on any 

 fixed geometrical^ plan about certain lines (the axes) as 

 crystals are. 



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