344 



On Chemical Tests. 



[Oct, 



pletely by boiling. Infusion of gall-nuts precipitates it orange red : 

 ferroeyanates, brown ; and metallic zinc produces a purple powder if 

 the solution be nearly neutral. Chemists are still far from being able 

 to separate titanic acid with accuracy from all other substances. 



a. The carbonated alkalies also precipitate titanium; and ifprus- 

 siate of potash gives a green colour it is, according to Lowitz, owing 

 to the presence of iron : an alkali dropped in after this test, produces a 

 purple precipitate, becoming blue and eventually, white. Zinc im- 

 mersed in weak solutions of titanium changes their colour from yellow 

 to violet, and ultimately to an indigo ; tin produces in them a pale red 

 tint which deepens to a bright purple red. Hydrosulphuret of potash 

 throws down a brownish red or according to others a dirty grass green 

 precipitate. Salts of titanium in solution are not decomposed by sul- 

 phuretted hydrogen. 



124. TUNGSTEN. Caustie or carbonated alkali produces in solu- 

 tions of tungsten white precipitates; prussiate of potash dirty yellow, 

 and tincture of galls brownish red. Sulphuretted hydrogen produces 

 210 precipitate. 



a. Tungsten has a greyish white colour like that of iron, and a good 

 deal of brilliancy. It is not magnetic. It is extremely hard and brittle, 

 and requires, a heat of 170° Wedgewood to melt it. 



125. URANIUM. A solution of uranium in nitric acid is yellow, 

 or inclining to yellow, and by proper evaporation crystals of a citron 

 yellow colour may be separated. In such solution the alkalies produce 

 a pale green or yellow precipitate insoluble in an excess of alkali ; fer- 

 rocyanate of potash a blood red precipitate ; iron, no precipitate. The 

 proto-salts of uranium are of a pale green or yellow colour, and are not 

 precipitated by carbonate of potash; Thomson says they are precipi- 

 tated by alkaline carbonates; but the precipitate is soluble in an excess 

 of the precipitant : the peroxide is of an orange colour j nut galls pro* 

 duce a chocolate coloured precipitate. 



a. No precipitate is produced in solutions of uranium by zinc, iron, 

 or tin. 



126. VANADIUM. The salts of vanadium are generally . of a fine 

 blue colour. Carbonated alkalies turn the solution brown. Muriatic 

 solution of vanadium is orange red, with a borax vanadium forms before 



