MICROCHEMICAL REACTIONS OF THE COMMON ELEMENTS 303 



EXPERIMENTS. 



a. Try reaction on salts of Ba, Sr and Ca, in acid, neutral and ammoniacal solu- 

 tions, and both in concentrated and in dilute solutions. 



b. Try mixtures of Ca and Ba, Sr and Ba; use solutions acidified with HC 2 H 3 O 2 , 

 decant the clear solution, and to it add NH 4 OH. 



c. Try the reagent upon Ba and Sr salts in HNO 3 solution. Then try it upon 

 Ag, Pb and mercurous salts in HNOs solution. 



Behavior with Primary Sodium Carbonate. 



An almost saturated solution of the reagent is added to the 

 dilute ammoniacal test drop by Method /, page 251. 



Calcium carbonate CaCOa separates in very small disks and 

 rhombs (H or 0). 



Strontium yields spherulites often of considerable size. 



Barium separates as minute spider-like aggregates and tiny 

 spherulites, the latter often uniting to form spindles and dumb- 

 bell-like masses. 



The addition of the reagent in solid form gives nearly as good 

 results. 



Warming the preparation increases the rapidity of the reac- 

 tion and leads to the formation of better crystals. 



Unless the test drop is quite dilute an amorphous precipitate 

 results. 



Ammonium carbonate can be substituted for the sodium salt; 

 the crystals then differ but little if any from those obtained as 

 above, but normal sodium carbonate gives amorphous precipi- 

 tates only and therefore should never be employed. 



When simple salts of the elements calcium, strontium and ba- 

 rium are employed it is not at all difficult to distinguish between 

 them by testing with primary sodium carbonate (or ammonium 

 carbonate). But if two or more of these elements are present 

 the method fails, characteristic crystals being the exception. 



In the presence of a great excess of the reagent a double 

 carbonate of calcium and sodium separates, having the formula 

 CaCO 3 - Na^COs 5 H 2 O, which crystallizes in stout monoclinic 

 prisms somewhat resembling the short, thin prisms of calcium 

 sulphate. Strontium and barium prevent the formation of the 

 double salt. 



