1839.] 



On Chemical Tests. 



343 



gles ; but in solutions of persalts of tin, it disengages hydrogen gas, and 

 causes a white gelatinous precipitate of peroxide of tin. 



c. Before the blow-pipe, salts of tin are easily discriminated by pro- 

 ducing a button of metallic tin . They should be added to a little soda 

 on charcoal and be submitted to the inner flame. 



d. Proto-salts of tin are easily recognized by their action with the so- 

 lution of gold, see 59; and 60, the persalts maybe distinguished by 

 giving with hydros ulphuret of ammonia a yellow precipitate which is 

 completely soluble in excess of the precipitant, and with liquid sulphu- 

 retted hydrogen, or a current of sulphuretted hydrogen gas; but in 

 these cases the yellow precipitate does not take place immediately. 



e. Nitric acid precipitates tin in the state of pure oxide. 



/. In an acid solution of antimony and tin with the assistance of a va- 

 pour bath heat, the antimony may be precipitated by immersing a plate 

 of tin and keeping the solution acid. The antimony should be well 

 washed and dried before it is weighed. 



122. TIN, proto-muriate of, is a delicate test for platinum, with the 

 solutions of which it produces an orange coloured precipitate. See 96. 

 It also detects gold producing a purple precipitate. See 59 and 60. With 

 the neutral salts of palladium this test gives a dark brown precipitate, 

 but if added in excess, the liquor remains of a fine transparent emerald 

 green colour. With a solution of corrosive sublimate it produces a 

 dark brown precipitate. The proto-nitrate of tin is said to be a more 

 delicate test than the proto-muria,te ; it yields with solutions of silvers 

 platina, palladium, and tellurium precipitates similar to that produced 

 in a solution of gold. 



a. This test is best when fresh made : it is apt to acquire a further 

 portion of oxygen from the atmosphere, and become a permuriate which 

 does not act like the proto-muriate. It should be kept in well stopt bot- 

 tles. 



b. Proto-muriate of tin reduces iron to a minimum of oxidation in those 

 compounds in which the metal is peroxidized : thus red sulphate of 

 iron is reduced by it to the green. It blackens the solution of corrosive 

 sublimate. 



123 TITANIUM, is precipitated from solutions in which it exists 

 as titanic acid, by ammonia, which gives a bulky precipitate simi- 

 lar to that of alumina. Titanic acid is also precipitated but not com- 



