ELOWPIPE REACTIONS. 87 



are the carbonates, sulphates, nitrates, and chlorides of the 

 alkaline metals. 



Testing for Alumina or Magnesia, — Cobalt nitrate, in solu- 

 tion, is used to distinguish an infusible and colorless mineral 

 containing aluminium from one containing magnesium. A 

 fragment of the mineral is first ignited, and then wet with a 

 drop or two of the cobalt solution and heated again. The alu- 

 minium mineral will assume a blue color, and the magnesium 

 mineral a pale red or pink. 



Any fusible silicate, when moistened with cobalt nitrate and 

 ignited will assume a blue color, hence this test is only deci- 

 sive in testing infusible substances. 



Infusible zinc compounds, when moistened with cobalt nitrate, 

 assume a green color. 



Testing for Lithium. — Some lithium minerals give the 

 bright purple-red flame if simply heated in the platinum for- 

 ceps. In other cases mix the powdered mineral with one part 

 of fiuorite and one of potassium bi-sulphate. Make the whole 

 into a paste with a little water, and heat it on the platinum 

 wire in the blue flame. 



Testing for Boron. — When the bright yellow-green of boron 

 is not obtained directly on heating the mineral containing it, 

 one part of the powdered mineral should be mixed with one 

 part of powdered fiuorite and three of potassium bi-sulphate ; 

 and then treated as in the last. The green color appears at the 

 instant of fusion. 



Testing for Fluorine. — To detect fluorine in fluorides mix a 

 little of the powdered substance with potassium bi-sulphate, 

 put the mixture in a closed glass tube and fuse gently. The 

 bi-sulphate gives off half of its sulphuric acid at a high temper- 

 ature, which acts powerfully on anything it can attack. If a 

 fluoride is present, hydrofluoric acid will be given oft", and the 

 walls of the tube will be found roughened and etched when the 

 tube is broken open and cleaned after the experiment. If a 

 silicate containing fluorine be powdered and mixed with previ- 

 ously fused salt of phosphorus, and heated in the open tube by 

 blowing the flame into the lower end of the tube, hydrofluoric 

 acid is given off, and the tube is corroded just above the assay. 



Silicates. — Nearly all silicates undergo decomposition with 

 salt of phosphorus, setting free the silica, forming a bead which 

 is clear while hot and has a skeleton of silica floating in it. 

 The bead is sometimes clear also when cold. 



Iron. — Minerals containing much iron produce a magnetic 

 globule when highly heated. Usually the reducing flame ia 



