MICROCHEMICAL REACTIONS OF THE COMMON ELEMENTS 295 



and salts of boric acid may sometimes interfere with the forma- 

 tion of typical crystals of strontium sulphate. 



EXPERIMENTS. 



a. To a drop of moderately dilute solution of SrCl 2 , add dilute H2SO4 and 

 examine at once. 



b. Recrystallize SrSO 4 from H 2 SO 4 and from HCl. 



c. Try to recrystallize SrSO 4 from HCl in the presence of H 2 SO4. 



d. Make a mixture of Ca and Sr salts and add H 2 SO 4 . Recrystallize the 

 product from H 2 SO 4 without having removed the Ca. In another portion remove 

 the Ca by extracting with boiling water and then recrystallize the residue. 



B. By Means of Oxalic Acid. 



See directions given under calcium, Method B, page 291. 

 The crystals of strontium oxalate are similar to those obtained 

 with calcium, but are usually distinctly larger, and crosses, 

 prisms, and four-pointed rosettes are more abundant and larger. 

 The crystals are either tetragonal or monoclinic depending upon 

 whether formed in the cold or separating from hot solutions. 



Precautions. 



To avoid error when testing with oxalic acid, it is always ad- 

 visable, after the crystals have well formed, to draw off the 

 supernatant solution and add dilute sulphuric acid to the pre- 

 cipitate. If no crystals of calcium sulphate appear after a few 

 minutes, add more acid and heat until white fumes appear, care- 

 fully observing the usual precautions. Transfer the drop of acid 

 to a clean slide, breathe on the drop and examine for fusiform 

 crystals of strontium sulphate. 



EXPERIMENTS. 



a. Test a drop of SrCl 2 solution with H 2 C 2 O 4 . 



b. Treat the oxalate thus obtained with H 2 SO 4 and recrystallize. 



BARIUM. 



Crystal Forms and Optical Properties of Common Salts 

 of Barium. 



A. ISOTROPIC. Nitrate (I). 



B. ANISOTROPIC. 



Hexagonal. Nitrite. 



