3 339.] 



On Chemical Tests. 



333 



c. The neutral phosphate, arseniate, borate and carbonate of potash, 

 and the fluoride and sulphuret of potassium turn reddened litmus paper 

 blue. 



d. Pure carbonate of potash dissolves in twice its weight of cold 

 water. Common carbonate of potash used as a test should first be exa- 

 mined ; it may contain sulphate and muriate of potash, and siliceous 

 and calcareous earths. Nitrate of silver, baryta, and oxalat e of am- 

 monia are proper tests to tr) r it with, after saturating it with pure nitric 

 acid. Potash also may be examined in the same way. A solution of 

 pure potash will remain transparent on the addition of barytic water. 

 Pure potash is apt to become carbonated by keeping even in glass stopt 

 bottles. 



99. POTASH, prussiute, or ferro-prussiate ; or ferro-cyanate. of, 

 is a valuable test : it forms precipitates with most of the metals, and 

 from the colour of the precipitate, the particular metal in many cases 

 may be inferred. It is not affected bv the alkalies. It is chiefly used 

 for detecting iron with which it produces a blue colour. See the table 

 of re-agents for its action with metals generally. 



a. If ferrocyanate of potash diluted with water gives immediately a 

 blue colour, or precipitate, with muriatic acid, it is not pure ; and may af- 

 ford fallacious results if so used as a test. - Neither sulphuretted hydro- 

 gen, the hylrosulphurets, the alkalies, nor the tincture of galls produce 

 any precipitate in solutions of this salt. 



lOO. POTASH, red ferrocyante of precipitates the profosalts of iron 

 blue or green according to the quantity in solution : but does not pre- 

 cipitate the persalts of iron. It is a more delicate test for protoxide of 

 iron than the common ferrocyanates. 



This test precipitates the following metals, and gives the follow- 

 ing coloured precipitates, viz. 



Tin . . . .White. Copppr Dirty brown. 



Silver Orange coloured. Cobalt and uranium Different 



Zinc... TDo. shades of reddish brown. 



Nickei ....... Brown. Mercury, protoxide, and ( peroxide. 



Bismuth Do. Brown. 



Titanium Do. 



101. potash, sulphate of acts as a test like sulphate of soda, 

 see 112. 



