328 



On Chemical Tests. 



[Oct. 



e. Pure protoxide of mercury is black: the peroxide is red, but when 

 finely pulverized it becomes somewhat yellowist). A strong heat decom- 

 poses both into metallic mercury, and oxygen gas. 



S3. fiSEROUlY, protomt?'ateof y mn.de by dissolving mercury in nitric 

 acid without heat, detects the following substances. 



a. Uncombined ammonia, with which it produces an ash-grey, or 

 black precipitate. 



b. Muriatic acid, which gives a white precipitate insoluble but turn- 

 ing black, in ammonia. 



c. Muriate of gold, which on adding the test gives a dense bluish 

 black precipitate. 



d. Muriate of platinum, producing an orange coloured precipitate. 



e. Phosphoric acid ; — a white precipitate is produced, soluble in an 

 excess of the test, and also in nitric acid. In testing for phosphoric 

 acid it is essential that no free alkali, or alkaline earth be present. 

 See 17. 



/. Sulphuric acid, indicated by a white crystalline or pulverulent 

 precipitate that becomes yellow when repeatedly "washed with boiling 

 water. 



84. MERCUm^ prussiate of , or cyanuret of , is a delicate test for 

 palladium, which it separates in the form of a yellowish white preci- 

 pitate. See 95. 



85. MERCURY, permuriate, oxymuriate, or perclihride of, may be 

 detected thus. Place a drop of its solution on a piece of clean polished 

 gold, and lightly rub the gold through the solution with the blunt point 

 of a penknife ; the part touched will become white See 53, 82. 



cl. Lime water throws down a lemon yellow precipitate, more lime 

 water produces a reddish yellow tint , a further quantity restores the 

 lemon yellow colour. Caustic potash produces a yellow precipitate. 

 Caustic ammonia causes a fine white flocculent precipitate which is a 

 triple compound of ammonia, chlorine and mercury. Carbonate of po- 

 tash gives a brick red precipitate of carbonate of mercury. Ferrocva- 

 nate of potash occasions a white precipitate of ferrocyanate of mercury, 

 which gradually but slowly becomes yellowish and at length pale blue. 

 Polished copper becomes tarnished, and if rubbed becomes of silvery 

 whiteness. Solution of albumen causes a white precipitate soluble in 

 excess of albumen. 



