and Laboratory Methods. 



1329 











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a. To the test drop add a little nitric acid, then the reagent. Ba is not 

 precipitated. Ca and 6"^ separate slowly in the usual form of their oxalates. 

 After allowing sufficient time for the complete separation of Ca and Sr, separate 

 the clear solution and to it add sodium or ammonium acetate. Ba is now pre- 

 cipitated, and can be identified from the crystal form of its oxalate. The precipi- 

 tated oxalates of Ca and Sr can be tested at once by adding sulphuric acid, or 

 they can be dried, heated, and thus converted into carbonates. The carbonates 

 can be dissolved in acid, and the solution thus obtained tested. 



d. To the test drop add ferric chloride sodium acetate, and then the reagent. 

 Ca and Sr appear in their normal form, and hence cannot be distinguished one 

 from the other ; but Ba separates as a double oxalate in the form of long fili- 

 form crystals of characteristic appearance. 



c. Oxalates of Ca, Sr, Ba undergo a marvelous change when precipitated in 

 the presence of stannic chloride. This beautiful method of distinguishing 

 between these elements is due to Behrens. 



To a drop of the moderately concentrated solution to be tested, which should 

 be neutral, or at the most only very faintly acid, add a 

 little stannic chloride ; stir, then add a fragment of oxalic 

 acid. 



Instead of the usual crystal forms, the oxalates separat- 

 ing in the presence of stannic chloride undergo a remark- 

 able change. Ca yields rounded and oval grains and thin 

 disks, with here and there crystals showing unmistakable 

 evidence of trying to develop into octahedra. The crystals 

 are never of large size, though larger than those of the nor- 

 mally formed oxalate, and apparently never grow into clear 



cut octahedra (Fig. 61). Sr under the same conditions yields large octahedra 

 (Tetragonal), clear cut and beautifully developed (Fig. 62). These crystals 



soon become corroded, and may eventually disap- 

 pear ; hence it is necessary to examine the prepara- 

 tion immediately after the addition of the oxalic acid. 

 Too much free mineral acid, or an excessive amount of 

 the stannic salt, interferes with the reaction. 



Ba is precipitated by oxalic acid under the above 

 conditions as neat, well developed prisms, singly, in 

 crosses, and in radiating masses (Fig. 63). If much 

 Ba is present, long, very pointed, fusiform crystals re- 

 sult, and bundles of slender, pointed needles. 



Mixtures of the alkaline earths do not yield, as 

 a rule, the characteristic forms above figured. The 

 form of the oxalates separating from such solutions 

 is then dependent upon the dominating element. 

 Since it is diflicult to properly describe the peculiar changes to be observed, the 

 student is advised to try the reaction on mixtures containing the elements of 

 the calcium group, taking care to have first one, then another of these elements 

 in slight excess. 



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I I I I I I 



^J3\v.= o.o»vT>»«i. 



Fig. 6i. 



\'p\M.-z.O-Oinif<^. 



Fig. 62. 



