324 SALTS. 



acid. The salt contains two atoms of acid to 

 one of base, and is therefore a biborate. It is a 

 white soluble salt, which swells up when heat- 

 ed, in consequence of the escape of its water 

 of crystallization. 



How is borax 825. PREPARATION. Borax is found in 

 prepared? solution in the water of certain shallow 

 lakes in India. It remains as an incrustation in the 

 beds of these lakes when they dry up in summer. It 

 is also prepared by the action of a solution of boracic 

 acid on carbonate of soda. 



What is said 826. BORAX GLASS. The light spongy 

 of borax glass? mass which is produced on heating borax, 

 may be melted down by greater heat and converted into 

 borax glass. This glass has the property of dissolving 

 metallic oxides, and receiving from them peculiar colors, 

 as described in a former paragraph. The chemist often 

 determines the metal which a salt or oxide contains, 

 by the color which it thus imparts to glass. The 

 method of making the experiment has already been 

 given. 



827. SOLDERING, WELDING, ETC. Borax 



Why is borax . . \ . 



employed in is employed in soldering metals, to keep 

 soldering? ^ metallic sur f aces clean. It does this 



by dissolving the coating of oxide which forms upon 

 them, and forming with it a glass which is fluid at a 

 high temperature, and easily pushed aside by the 

 melted solder. Its use in welding iron depends on the 

 same property. Borax is employed, to some extent, in 

 medicine. It is also a constituent of the glass called 



