3835.] 



on Dysluite. 



289 



From the preceding analysis the constituents of dysluite 

 appear to be 



Alumina - - - - - 



Oxide of zinc - - - 

 Peroxide of iron - - 

 Protoxide of manganese 

 Silica ------ 



Water 



If we admit the silica to be only an accidental mixture, 

 it is evident that dysluite consists of 

 8 atoms alumina 

 2 ,, oxide of zinc 

 5 ,, peroxide of iron 

 1 ,, protoxide of manganese 

 The alumina obviously acts the part of an acid, as it does 

 in spinell, automolite, sapphirine, and candite. But in all 

 of these, several atoms of alumina unite with one of the 

 bases, which are manganese and peroxide of iron. But 

 dysluite is composed of simple aluminates, the formula 

 exhibiting its constitution being 



5/A1. + 2ZA1. + mn Al. 

 It is worthy of remark, that the crystalline form of dys- 

 luite is the regular octahedron, the same form which spinell 

 and all the other crystallized minerals, in which alumina 

 acts the part of an acid, assume. 



Note. — The four minerals mentioned, in which alumina 

 acts the part of an acid in union with a base, have their 

 composition represented by the following formulae, as 

 deduced from analyses made in the laboratory at Glasgow. 



VOL. I 



