MICROCHEMICAL REACTIONS OF THE COMMON ELEMENTS 295 



A. ISOTROPIC. Nitrate (I). 



B. ANISOTROPIC. 



Hexagonal. 



Tetragonal. 



Orthorhombic. Chlorate; sulphate. 



Monodinic. Acetate; chroma te. 



Tridinic. Chloride. 



DETECTION. 



A. By Means of Sulphuric Acid. 



First obtain a precipitate of strontium sulphate by 

 Method /, page 251. Examine it with the microscope to learn 

 the character of the solid phase. Then proceed with the identi- 

 fication of the practically amorphous precipitate by recrystal- 

 lization from concentrated sulphuric acid by Method XII, 

 page 264, or from concentrated hydrochloric acid by the same 

 method. 



Rarely, strontium sulphate separates in the cold in crystal 

 form. Heating with concentrated sulphuric acid and gently 

 breathing upon the preparation yields at first globular masses 

 and tiny rhombic plates of a salt of the formula SrSC>4 (or some- 

 times probably SrSC^ H^SC^) . These tiny plates eventually 

 develop into more or less irregular spindle-shaped crystals, 

 which gradually enlarge at the middle until they become irregular 

 crosses with two very short arms. The appearance is very 

 characteristic. The only element liable to lead to error is lead 

 which often first assumes forms closely resembling those of stron- 

 tium, later growing into crystallites which may be mistaken for 

 barium. 



Recrystallized from concentrated hydrochloric acid strontium 

 sulphate has an entirely different habit. Square and rectangular 

 plates appear followed by thin prisms and sheaves of slender 

 pointed crystals. The solubility of strontium sulphate in hydro- 

 chloric acid is quite low, hence it is necessary to employ a large 

 drop of the solvent and therefore it is seldom that all the pre- 

 cipitate will dissolve. It follows that to obtain the best results 

 the solvent should be decanted from the precipitate immediately 



