and Laboratory Methods. 



1295 



of characteristic crystals of barium sulphate, it is advisable to draw off the super- 

 natant liquor after the addition of the reagent and before heating with an excess 

 of the acid. When dealing with mixtures it is always best to proceed in this 

 manner. 



Exercises for Practice. 



Try above method on a simple salt of Ba. 



Make a mixture of Ca and Ba, recrystallize at once without removing the Ca. 

 From another portion remove the Ca with hot water and recrystallize the residue. 



Try a mixture of Sr and Ba. Remove the Sr by treating with HCl and recrys- 

 tallize the residue. 



Try a mixture of Ca, Sr, and Ba ; first recrystallizing at once, then removing 

 in turn the Ca with hot water and the Sr with HCl. 



After having tried the other reactions for barium, described below, fuse some 

 BaSO^ with K2CO3 and proceed as directed above. 



//. Oxalic Acid precipitates Barium Oxalate from solutions of salts of Barium. 

 BaCl2 + H2C2O4 = BaC^O^ . //H2O + 2HC1. 



Method. — To a drop of a very dilute solution of the barium salt add sodium 

 acetate and then oxalic acid in the same manner as in testing for calcium and 

 strontium. In a few seconds large branching aggre- 

 gates in the form of radiating bundles and sheaves 

 of fibrous needles are seen. These radiating masses 

 occasionally assume forms resembling snow crystals. 

 Rarely well developed monoclinic prisms are ob- 

 tained. 



The usual forms of barium oxalate are shown in 

 Fig. 55. 



Remarks.— The. solution to be tested should be 

 neutral.' A slight trace of acid is apt to prevent 

 the separation of the characteristic crystals. 



If no crystals appear after a short time, add a 

 fragment of sodium or ammonium acetate. 



When calcium or strontium are present the 

 characteristic crystal forms of barium oxalate will 

 not be obtained. Recourse may then be had to 



testing in dilute nitric acid. From nitric acid solutions the barium salt will not 

 separate, while the oxalates of calcium and strontium will slowly crystallize in 

 their usual form. After allowing sufficient time for the complete separation of 

 calcium and strontium, draw off, concentrate the solution, and add sodium 

 acetate. Barium oxalate now appears, usually in the form of rosettes of thin 

 prisms. 



Barium oxalate, like the oxalates of calcium and strontium, assumes different 

 crystal forms according as the test drop is hot or cold. Hot solutions give rise 

 to the production of strongly polarizing orthorhombic plates. 



Since, in order to facilitate the separation of barium oxalate, sodium acetate 



