1839.] 



On Chemical Tests. 



319 



Ammonia. A white precipitate insoluble in ammonia : acetate of 

 lead is not affected by ammonia, but after some time a subsalt is de- 

 posited. 



cZbZTe ^ammonia } A white P reci P i{ate soluble in P ure P otash " 

 Phosphate o f soda. The same, but the solution must be neutral. 



( Pmll"au% potash } In neutral solutions, a white precipitate. 

 Red prussiate of potash. No precipitate. 



Hydrosnlphuret of ammonia. A black precipitate insoluble in excess. 



Metallic zinc, precipitates metallic lead in blackish grey shining 

 spangles, or if it be suspended by a silk line in a solution of lead the 

 latter forms around it a crystalline arborescence. 



70. LEAD, acetate of, detects (a) sulphuric acid; (6) muriatic acid; 

 (c) alkaline and earthy carbonates ; (d) phosphoric acid ; (e) hydro- 

 sulphurets and sulphuretted hydrogen; (/) carbonic acid; and (#) 

 fooracic acid. 



a. Sulphuric acid, and the alkaline sulphates are detected by giving 

 a white precipitate of sulphate of lead. 



b. Muriatic acid is also detected by giving a white precipitate, which 

 is muriate, or chloride of lead. 



c. Alkaline and earthy carbonates are detected by a white precipi- 

 tate ; but if the solution in which they are contained be first saturated 

 with nitric acid the test does not discover them. 



d. Phosphoric acid and phosphates produce with this test, a white pre- 

 cipitate that melts before the blow-pipe into a pearl white globule, which 

 eventually becomes pure lead. 



e. Hydrosulphurets, and sulphuretted hydrogen turn black on the 

 application of this test. 



/. Carbonic acid is better discovered by other tests than by acetate 

 of lead. 



g, So also is boracic acid, see 3. 



71. lead, subacetate of deprives wine of its colouring matter. It 

 acts on a variety of animal and vegetable matters, and is not therefore a 

 discriminative test. 



a. If acetate, or subacetate of lead used for testing should be mixed 

 with acetate of lime, or baryta, the former i. e. lime may be detected by 

 adding to a dilute solution, oxalic acid, or oxalate of ammonia ; and the 

 latter by sulphuric acid, the solution being largely diluted. Acetate of 



