64 50. BASES AND ACIDS WITH REAGENTS. 



not the washings), to compensate for the solubility of the 

 salt in the ammoniacal solution in which it was precipi- 

 tated. [Fresenius.) 



The residue contains 36.04° 1^ of magnesic oxide or 

 magnesia, MgO. 



If the solution containing the magnesium is strongly- 

 acid. Rose recommends that the sodic phosphate be added 

 first, and then a sufficient quantity of ammonia to super- 

 saturate the acid ; thus he prevents the formation of any 

 hydrated magnesic oxide that is liable to be precipitated 

 with the phosphate and make it impure. 



h. Separation of Calcium and Magnesium. — This is 

 effected with ammonic oxalate in the presence of am- 

 monic chloride, and ammonia in slight excess. Add the 

 ammonic chloride and ammonia as directed above in r', 

 and then ammonic oxalate ; this last reagent must be 

 added in slight excess, after it has ceased to give any 

 further precipitate of calcic oxalate, in order to convert 

 all the magnesium into oxalate. Let the tmixture stand 

 12 hours in a moderately warm place, decant the clear 

 liquid into the filter, wash the precipitate in the beaker 

 once with water, decant the washings, dissolve the pre- 

 cipitate in a little dilute hydrochloric acid, add ammonia 

 in slight excess, and ammonic oxalate ; let the mixture 

 stand until the precipitate has completely subsided, then 

 filter through the same filter as before, and wash. The 

 first filtrate has the larger portion of the magnesium in 

 it ; the second, the rest. 



Acidify the second filtrate, and concentrate that and 

 the washings by evaporation, add the residue to the first 

 filtrate, and precipitate magnesium in this solution as 

 phosphate. Treat the precipitate of calcic oxalate on the 

 filter as directed in § 49. 



If, in the filtrate from the calcic oxalate, there is a 

 great excess of ammonic salts, it will be safer to evapo- 

 rate the solution to dryness and expel them by ignition, 



