SILICON. 181 



with the emerald, is usually crystallized in six- 

 sided prisms, terminated by trihedral pyramids. 

 It has a fine green colour, a foliated texture, 

 and a specific gravity of 3-3. It is a conductor 

 of electricity. From an analysis of this mineral 

 by Lowitz, we learn that its constituents are 



Silica . . 33 



Peroxide of copper . 55 



Water . . 12 



100 



Let us calculate the constituents of this mineral 

 on the supposition that it is a hydrated sesqui- 

 silicate of copper ; that an atom of silica weighs 

 2, an atom of oxide of copper 5, and an atom of 

 water 



(1.) 5 (atom of oxide of copper) : 3 (1J atom silica) : : 55 : 



33 = the silica united to the oxide. 

 (2.) 88 : 12 (water in mineral) : : 8 : 1-0905 = water in the 



mineral, very nearly 1 atom. 



Hence the mineral is composed of 



j silica 33 

 \ oxide 55 

 1 atom water . . . 12-37 



1 integ. part, of sesquisilicate of copper 4 S I 88 



t oxide 55 J 



100-37 



This mineral gives us exactly 2 for the atomic Gives 2. 

 weight of silica. There is a slight deficiency in 



M3 



