CONFIRMATORY TESTS. 31 



Zinc. If the incrustation be heated with the nitrate of 

 cobalt solution, it becomes green. 



To detect certain common substances associated with 

 metals : 



Alumina. This is known by its adhering readily to the 

 tongue when licked. Tested before the blowpipe with 

 nitrate of cobalt, it becomes blue. 



Lime. This gives a very bright light when heated before 

 the blowpipe flame. It is infusible even with carbonate of 

 soda, and so differs from silica and flinty substances. 



Carbonate of Lime effervesces when a little hydrochloric 

 or citric acid is dropped on it. 



Magnesia. When heated with nitrate of cobalt solution, 

 becomes flesh red. 



( Soda. When strongly heated, gives a reddish yellow 

 < colour to the outer flame. 

 ( Potash gives a violet colour to it. 



Sulphur is known by its characteristic odour when the 

 substance is roasted. If a portion of the heated mineral be 

 placed on a moistened piece of silver, a black stain shows 

 the presence of sulphur. 



Arsenic is known by its characteristic garlic odour when 

 heated. 



All carbonates effervesce in acids.* (N.B. A limestone rock, 

 which is made up of carbonate of lime, can thus be easily 

 distinguished from a sandstone, &c.) 



Certain silicates, when acted on by acid and heated, 

 gelatinize. 



N.B. A blowpipe for temporary use may be made thus : Procure 

 a long pipe of glass tube (|- inch thick). Hold it horizontally over 

 the flame of a spirit lamp. As the middle part becomes softened pull 

 both ends of the tube horizontally, until the middle part of the tube is 

 about the thickness of an ordinary blowpipe jet. File a notch on the 

 thin part, and snap the tube. Now take one portion and again heat it 

 (a little distance from the nozzle) , and bend it so that the nozzle may 

 be inclined at an angle to the longer branch. 



* Citric acid, which can be conveniently carried about as crystals 

 and dissolved in a little cold water, is a most useful re-agent. Nearly 

 every carbonate can be dissolved with effervescence in a cold solution. 

 Spathic iron requires a boiling solution. 



