346 ELEMENTARY CHEMICAL MICROSCOPY 



d. If barium borate is at hand, try testing it for Ba. 



e. Try H2C2O4 on a salt of Mg, then add an excess of HC2H3O2 to the test drop 

 and examine again. 



/. Test salts of Zn, Cd, Pb and Ag. 



BEHAVIOR OF CALCIUM, STRONTIUM AND BARIUM 

 TO OTHER IMPORTANT REAGENTS. 



The tests already given are generally ample for the proper 

 identification of the alkaline earths, but occasionally problems 

 arise where supplementary or alternate methods are desirable. 

 The following reactions have, therefore, been included both on 

 account of their applicability to the examination of unknown 

 material and because of the further light they throw upon the 

 similarities and differences between the members of the Calcium 

 Group. 



Behavior with Potassium Ferrocyanide. 



The reagent is applied by Method /, page 299, to the test 

 drop acidulated with acetic acid and containing a little ammo- 

 nium chloride. 



Calcium yields tiny rectangular or square plates. 



Strontium fails to form a ferrocyanide under the conditions 

 given above. 



Barium yields large, clear, transparent, yellow rhombs prob- 

 ably belonging either to the orthorhombic or to the triclinic 

 system, depending upon the amount of water of hydration. 



The salts separating are double ferrocyanides to which the 

 following formulas have been ascribed: K 2 CaFe(CN) 6 • 3 H 2 

 and K 2 BaFe(CN) 6 • 5 H 2 (O?) or K 2 BaFe(CN) 6 . 3 H 2 (Tr). 

 As usually obtained the barium salt extinguishes parallel to a 

 line drawn through the acute angles of the rhombs. This fact 

 enables the analyst to readily differentiate between the double 

 barium salt and chance separation of the reagent (M). 



Free mineral acids must be absent. 



Potassium ferrocyanide, though giving a neat reaction with 

 pure salts of barium, is of little value when dealing with mix- 

 tures. It is then often difficult to avoid the precipitation of 



