172 COMPOSITION OF THE BODY 



precipitate = silver sulphide. A white precipitate which does not 

 dissolve in dilute HNO 3 and which darkens in the sunlight = sil- 

 ver chloride. 



4. Add hydrochloric acid and heat ; render alkaline with am- 

 monia, add (NH 4 ) 2 C 2 O 4 , and allow to stand. A white precipi- 

 tate occurs if calcium is present. 



5. Precipitate calcium as directed in 4, filter, and to the filtrate 

 add NH 4 OH and Na 2 HPO 4 . If magnesium is present a precipi- 

 tate will be formed, though perhaps slowly. 



6. If magnesium is found it must be removed before testing for 

 sodium or potassium. After precipitating the calcium, filtering 

 and evaporating the filtrate to dryness, the residue should be ig- 

 nited to remove ammonium salts. Heat the residue gently with a 

 little water, add baiyta water or milk of lime, free from alkali, till 

 precipitate ceases to form. Boil, filter and add to the filtrate a slight 

 excess of ammonia and ammonium carbonate in mixture. After 

 warming for some time, filter and evaporate the filtrate to dryness 

 with a little NH 4 C1, ignite with low heat until all ammonium salts 

 have been volatilized and dissolve the residue in a little water. 



(a) A drop of the concentrated solution held in the flame gives 

 a yellow color if sodium is present. 



(b) Add to the remainder of the solution a little hydrochloro- 

 platinic acid, H 2 PtCl 6 . A yellow crystalline precipitate indicates 

 potassium. It may require some time for this precipitate to form. 



The residue from the aqueous extract (Solution I.), after washing, 

 should be treated with hydrochloric acid. Add a few drops of sul- 

 phuric acid,and evaporate to dryness. Treat the residue with a little 

 hydrochloric and nitric acid, add water, heat gently and filter (Solu- 

 tion II.). On portions of this solution perform the following tests : 



1. Add sodium carbonate with constant stirring until the pre- 

 cipitate formed ceases to redissolve. Add sodium acetate and a 

 little acetic acid. A yellowish white precipitate indicates ferric 

 phosphate. 



2. Add ammonium hydrate. A light green precipitate changing 

 to reddish brown indicates iron. If no change in color is observed 

 in a white gelatinous precipitate aluminum is probably present. 



