CHAP. IX. 



OF THE ATOMIC WEIGHTS OF THE EARTHS 

 PROPER. 



THERE are four substances, which are now 

 considered as metallic oxides, but which were 

 long distinguished by the name of earths proper. 

 When pure, they have the form of white taste- 

 less powders, insoluble in water, though capa- 

 ble of forming solid hydrates with that liquid. 

 They combine readily with the acids, and form 

 salts, which redden vegetable blues, and are de- 

 composed by exposure to a red heat. These 

 four bodies are alumina, glucina, yttria, and zir- 

 conia. We shall devote this chapter to the in- 

 vestigation of the atomic weights of these bo- 

 dies. 



SECT. I. 



OF THE ATOMIC WEIGHT OF ALUMINA. 



IN a paper inserted in the Annals of Philoso- 

 phy (Second Series), Vol. III. p. 61. I gave the 

 result of a very laborious analysis of alum, from 

 which I drew, as a conclusion, that the atomic 

 weight of alumina was 2*25. Since that time, Mr. 



