332 



On Chemical Tests. 



[Oct. 



Phosphate of soda, oxalic acid, cyanurct of mercury, and protosul- 

 phatc of iron produce no precipitate. 



Hydrosulphuret of ammonia and sulphuretted hydrogen produce a 

 brown, or brownish black precipitate. Metallic zinc precipitates pla- 

 tinum in the state of a black ^metallic powder. 



a. Solutions of chloride of platinum do not affect litmus paper j but 

 solutions of the oxide redden it- 



b. Before the blow-pipe the compounds of platinum are completely 

 reduced, and impart no colour to the fluxes. 



c. Potash and ammonia discriminate platinum from all other sub- 

 stances; the solution should be acid. 



d. If lime water be added to a neutral solution of platina, and it be 

 exposed to the sun's rays, an instant copious white precipitate will oc- 

 cur ; if the platina be in excess the precipitate will be pale yellow. A 

 neutral solution of platina is decomposed by oxalic acid, as well as by 

 the oxalates, in the sun's rays, with a copious disengagement of gas. 



97. PLATINA, muriate or chloride of, is a valuable test for distin- 

 guishing the salts of potash from the salts of soda; it produces with 

 all the salts of potash a yellow precipitate but it does not arfect salts 

 with a base of soda. It is essential when this test is used, that there be 

 neither ammonia, nor excess of acid present in the solution, which should 

 be somewhat concentrated. It is also a test for tin, see 121. 



The action of this test with the salts of ammonia is the same as with 

 salts of potash. See 28 c, and the next article. 



98. POTASH and its salts, distinguished from soda and its salts; 

 also from ammoniacal salts, see 28, 110 a. The best re agents for de- 

 tecting potash in solutions are the chloride of platinum, and tartaric 

 acid. But as the chloride of platinum acts towards ammoniacal salts 

 in the same manner as towards the salts of potash, the ammonia in so- 

 lution, if any, must be first removed when testing for potash with this 

 re-agent. 



a. If a concentrated solution of sulphate of alumina be dropped into 

 a salt of potash, octahedral crystals of alum will be soon deposited. 



b. Salts of potash may be thus distinguished. Fuse before the blow- 

 pipe a little borax to which a small portion of oxide of nickel has been 

 added. A yellowish glass is obtained. Fuse tlTis yellowish bead with 

 a little of the salt under examination and if it contain potash the bead 

 will assume a bluish or violet colour, 



