90 STRONTIA. SILICA. 



It slakes in the air like lime, is soluble in water, 

 and also in alkohol, the flame of which it causes 

 to assume a yellow colour. It is a deadly poison. 

 It is also found to consist of oxygen and a metallic 

 base called barium. 



Carbonate of barytes is found as a mineral, but it 

 is not abundant. 



Sulphate of barytes is found native more fre- 

 quently. When calcined, it forms the Bolognian 

 phosphorus. 



Barytes is used as a white paint under the name 

 of permanent white, not being liable to change its 

 colour. 



STRONTIA. 



The name of this earth is derived from Strontian, 

 in Argyllshire, in Scotland, where it was first dis- 

 covered by Dr. Hope. 



It is soluble in water, and changes vegetable 

 blues to green. 



It is also considered to be the oxide of a metal 

 called strontium. \ 



Strontia is not very abundant, and is always in 

 nature found combined with the carbonic or sul- 

 phuric acids. 



The other salts of strontia are but little known. 

 All the salts of Strontia have the property of tinge- 

 ing the flame of alkohol red. 



SILICA. 



This earth, which forms a large portion of the 

 surface of the earth, exists nearly pure in flint and 

 rock-crystal : hence it has been called the earth of 

 flints. 



It may be obtained pure as follows : "calcine 



