230 ANALYTICAL CHEMISTRY. 



be white, a dark color indicating iron (or possibly other heavy 

 metals). 



Calcium hypochlorite (bleaching-powder) has to be examined by 

 quantitative methods to ascertain the amount of hypochlorous 

 acid present. 



Examination of magnesium compounds. Magnesium sulphate, 

 oxide, and carbonate, the two latter after being dissolved in diluted 

 hydrochloric acid, should not be precipitated by hydrosulphuric 

 acid, nor by ammonium hydrate, sulphide, or carbonate after 

 a sufficient amount of ammonium chloride has been added 

 (absence of heavy metals and alkaline earths). 



Magnesium, sulphate should be tested for chlorides by the addi- 

 tion of silver nitrate. 



Water digested with the oxide or carbonate should leave no 

 residue upon evaporation. The same compounds, dissolved in 

 nitric acid, should not be precipitated by either barium chloride 

 or silver nitrate. The oxide should not effervesce with acids 

 (absence of carbonic acid). 



Examination of aluminium compounds. Aluminium sulphate and 

 aluminium-potassium sulphate (alum) when dissolved in water, or 

 aluminium hydrate when dissolved in sulphuric acid, should not 

 be precipitated by hydrosulphuric acid and show no blue color 

 on the addition of potassium ferrocyanide (absence of iron). 

 Potassium or sodium hydrate, added to the above solutions, 

 should cause a white, gelatinous precipitate, which is com- 

 pletely dissolved by an excess of the reagent. Water digested 

 with aluminium hydrate should leave no residue upon evapo- 

 ration. 



Examination of compounds of iron. The solution of ferrous 

 salts, acidulated with hydrochloric acid, should not be precipi- 

 tated by hydrosulphuric acid; solutions of ferric salts give with 

 the same reagent an almost white precipitate of sulphur; a 

 more or less colored precipitate would indicate the presence of 

 metals of the arsenic or lead group. 



Solutions of ferric salts (or of ferrous salts, after they have 

 been converted into ferric salts by heating with hydrochloric 

 and nitric acids), after having been precipitated by an excess of 



