DETECTION OF IMPURITIES. 229 



latter), after being supersaturated with nitric acid, should be 

 tested with solution of barium chloride and silver nitrate for 

 sulphates and chlorides. 



Bicarbonates may contain carbonates; the latter are indicated 

 by a white precipitate formed with barium chloride in the cold 

 solution ; bicarbonates are not precipitated by this reagent in 

 the cold. 



Iodides may contain an iodate, which is indicated by a blue color 

 on the addition of gelatinized starch and some diluted sulphuric 

 acid; chlorides and bromides may be detected by precipitating 

 a solution of the iodide with an excess of silver nitrate, collect- 

 ing and washing the precipitated iodide (bromide and chloride) 

 of silver, and digesting it with ammonium hydrate, which dis- 

 solves the chloride and bromide, but not (or only traces of) the 

 iodide; the filtered ammonium solution, upon being supersatu- 

 rated with nitric acid, will give a white precipitate if chlorides 

 or bromides are present; a slight turbidity may be due to traces 

 of dissolved iodide. 



Potassium salts should impart a violet color to a non-luminous 

 flame, a yellow color indicating sodium. 



All compounds of ammonium should be completely volatilized 

 by heat without leaving a residue. 



Examination of compounds of calcium. Calcium chloride and 

 calcium carbonate, the latter after having been converted into 

 chloride by neutralizing with hydrochloric acid, should not be 

 precipitated by hydrosulphuric acid or by ammonium hydrate 

 (absence of heavy metals and of aluminium) ; the solution, 

 after adding ammonium hydrate, ammonium chloride, and an 

 excess of ammonium carbonate, and filtering off the precipitated 

 calcium carbonate, should not be precipitated by sodium phos- 

 phate (absence of magnesium). Water digested with calcium 

 carbonate or with tricalcium phosphate, should leave no residue 

 upon evaporation. 



Calcium carbonate and phosphate should be tested for sulphates 

 and chlorides by dissolving the salts in diluted nitric acid and 

 adding barium chloride and silver nitrate. 



Iron will be indicated in calcium phosphate by saturating its 

 solution in hydrochloric acid with hydrosulphuric acid, and then 

 adding an excess of ammonium hydrate; the precipitate should 



