62 50. BASES ANT> ACIDS WITH IlEAGENTS. 



of the standard permanganate solution, as directed in 

 § 69, a. This method yields results that are hardly less 

 accurate, if any at all, than the other two already de- 

 scribed. For each equivalent of oxalic acid found, ex- 

 pressed in milligrammes^ reckon one equivalent of lime, 

 similarly expressed, or 0.028 grm. 



If the amount of calcic oxalate in the filter is very 

 small, it may be converted into sulphate by ignition with 

 pure ammonic sulphate, and the lime weighed as sulphate, 

 containing 41.18 "1^ of lime. 



b. If the acid in combination with the lime is one that, 

 like phosphoric acid, cannot be readily removed, add am- 

 monia until a permanent precipitate just begins to appear, 

 dissolve this by adding a few drops of hydrochloric acid, 

 add ammonic oxalate in excess, then sodic acetate, and 

 proceed as in a with the precipitated calcic oxalate. 



MAGNESIUM. Mg. 24. 



50. Compounds of magnesium with phosplioric, car- 

 bonic, oxalic, and silicic acids, and with fluorine, are in- 

 soluble or sparingly soluble in water. The silicate and 

 fluoride are insoluble in acids. 



Reactions. — The carbonate is not precipitated from so- 

 lutions of magnesic salts containing much ammonic chlo- 

 ride, on addition of an alkaline carbonate. 



Hydric disodic phosphate produces a white precipitate 

 of ammonio-magnesic phosphate, MgNH^PO,, in solutions 

 of magnesic salts containing ammonic salts. The precipi- 

 tate, at first flocculent, if at all abundant, becomes more 

 granular and crystalline after standing some time, or after 

 violent agitation of the liquid containing it. If the solu- 

 tion of the magnesic salt is very dilute, the precipitate 

 may not appear for some hours, and then it is crystalline 

 and adheres to the sides of the tube ; if, before the solu- 

 tion was set aside, it was stirred with a glass rod, and'the 



