60 § 49. BASES AND ACIDS WITH REAGENTS. 



Reactions* — If dilute sulphuric acid or amnionic sul- 

 phate is added to a not too dilute solution of a calcic salt, 

 free from a large excess of strong acids, a white precipi- 

 tate of calcic sulphate, CaSO^, 2}Ifi, is formed immedi- 

 ately or after standing some time, which is soluble in an 

 excess of mineral acid, and slightly soluble in acetic acid 

 and water. 



This sulphate being much less soluble in alcohox than 

 in water, the addition of a quantity of this reagent about 

 equal to the volume of the solution, will often cause the for- 

 mation of a precipitate, at least after standing some time,' 

 that would otherwise not appear. 



This precipitate is readily decomposed when boiled 

 with a solution of sodic carbonate, calcic carbonate and 

 sodic sulphate being formed. 



Ammonic oxalate gives, even in very dilute solutions 

 of calcic salts, if they contain no free mineral acid, a 

 white crystalline precipitate of calcic oxalate, CaC.^O^, 

 soluble in hydrochloric or nitric acid, and insoluble in 

 acetic acid or a solution of ammonic chloride. If the so- 

 lution of the calcic salt is very dilute, a precipitate may 

 not appear until after the mixture has stood some time. 



Quantitatiye Estimation. — Calcium is usually deter- 

 mined as carbonate, CaCO^, by precipitation Avith am- 

 nionic oxalate and conversion of the oxalate into carbon- 

 ate by ignition. 



a. 1 . — If the salt is soluble in water or the acid is one 

 that, like carbonic acid, may be expelled by hydrochloric 

 acid, or can be removed by evaporation to dryness, like 

 silicic acid, or the solution gives no precipitate with am- 

 monia, add ammonic oxalate to the hot solution free from 

 any great excess of acid, and then ammonic hydrate until 

 the liquid, after being well stirred, gives oif an ammoni- 

 acal odor, let the mixture stand in a wann place 12 hours, 

 decant the clear liquid into a filter, wash the preci|5itate 



