336 



On Chemical Tests* 



[Oct, 



c. Metallic iron, copper, or zinc precipitates silver, metallic ; near the 

 zinc the silver is black, further from it white. 



d. Muriatic acid and the chlorides give white curdy precipitates, 

 when much silver is held in solution, but only an opalescence if it be 

 in small quantity. 



Protosulphate of iron precipitates silver in a white metallic state. 

 f. Before the blow-pipe salts of silver are reduced to the metallic state 

 by fusion with soda on charcoal. 



107. SILVER, acetate of, acts as a test precisely like the nitrate of 

 silver; but it is sometimes more convenient to use it in analysis than 

 the nitrate. 



108. SILVER, nitrate of is an excellent test for discovering muria- 

 tic acid, and chlorine, as well as muriates and chlorides. It produces 

 with them white curdy precipitates that blacken in the sun, and that 

 are soluble in ammonia. As this test is acted on by alkaline and earthy 

 carbonates, and by sulphuric and sulphurous acids, and their combina- 

 tions, these acids must be first removed by nitrate, or acetate of barytes, 

 and the alkaline, or earthy carbonates, by fully saturating them with 

 nitric acid. Carbonate of silver is soluble in dilute nitric acid with 

 effervescence : the muriate or chloride of silver is not. See also 15 and 

 106, for other substances which act on solutions of silver. 



a. With the assistance of an alkali, nitrate of silver is a test for de- 

 tecting minute portions of arsenic, with which it produces a yellow 

 precipitate, see 39. It likewise indicates minute portions of sulphuret- 

 ted hydrogen, and hydrosulphurets in general, producing with them 

 a black precipitate of sulphuret of silver. With chromic acid it yields 

 a carmine red precipitate of chromate of silver. Vegetable extractive 

 matter also acts on nitrate of silver ; the precipitate is brown and dis- 

 solves in nitric acid. 



b. Nitrate of silver detects hydro-cyanic acid with which it produces 

 a white precipitate of cyanide of silver even in a very dilute solution 

 of the acid. This precipitate is distinguished from other white precipi- 

 tates of silver by its being insoluble in nitric acid at ordinary tempera- 

 tures, but readily soluble at a boiling heat; and by its retaining its pure 

 white colour when exposed to the rays of the sun, see 10. -Cyanide of 

 silver when dried and heated emits cyanogen gas which is easily known 

 by the beautiful rose red colour of its flame. , 



c. Fused nitrate of silver may be contaminated as a test with cop- 

 per, and perhaps with gold. But both are said to be precipitated on 

 the caustic being dissolved in water. If nitrate of silver be made by 



