C 138 ] 



iron and silica in the other oriental gems. In the state 

 in which it is procured by chemists, it appears as a 

 white ppwder, soluble in acids and fixed alkaline li- 

 quors. From my experiments, it appears that alumi- 

 na consists of one proportion 33 of aluminum, and 

 one 15 of oxygene. 



4. Magnesia exists in a pure crystallized state, 

 constituting a mineral like talc found in North Ame- 

 rica. In its common form it is the magnesia usta, or 

 calcined magnesia of druggists. It generally exists in 

 soils combined with carbonic acid. It is soluble in all 

 the mineral acids; but not in alkaline lixivia. It is dis- 

 tinguished from the other earths found in soils by its 

 ready solubility in solutions of alkaline carbonates, 

 saturated with carbonic acid. It appears to consist of 

 38 magnesium and 15 oxygene. 



5. There are two well known oxides of iron^ the 

 black and the brown. The black is the substance that 

 flies off when red hot iron is hammered. The brown 

 oxide may be formed by keeping the black oxide red 

 hot, for a long time in contact with air. The first 

 seems to consist of one proportion of iron 103, and 

 two of oxygene 30; and the second of one proportion 

 of iron 103, and three proportions of oxygene 45. 

 The oxides of iron sometimes exist in soils combined 

 with carbonic acid. They are easily distinguished from 

 other substances by their giving when dissolved in 

 acids a black colour to solution of galls, and a bright 

 blue precipitate to solution of prussiate of potassa and 



iron. 



6. The oxide of manganeswn is the substance com- 

 monly called manganese, and used in bleeching. It 



