308 



On Chemical Tests. 



[Oct. 



■which is insoluble in a solution of sulphate of potash, and sparingly 

 soluble in water. 



b. A mixture of cerium and iron may be separated, by boiling in 

 oxalic acid ; the iron dissolves and the cerium is left in the state of a 

 white powder decomposable by heat, see 65 d. 



c. Solutions of protoxide of cerium are distinguished from those of 

 alkalies, barytes, strontian, lime and magnesia, in the same manner as 

 solutions of alumina are distinguished from those substances, see 26 c. 

 From alumina and glucina, the protoxide of cerium is distinguished by 

 its insolubility in an excess of potash j from thorina, by its relation to 

 heat. The latter does not become red when ignited, neither does it 

 give a coloured bead when fused with borax, or microcosmic salt, before 

 the blow-pipe. When this proof is made, the substance must of course 

 have been freed from iron. Protoxide of cerium is distinguished from 

 yttria in the same manner as from thorina, and also by its behaviour 

 towards a solution of sulphate of potash. 



47. CHLORINE, Muriates or chlorides are detected by nitrate of 



silver which produces a white precipitate of muriate, or chloride of silver 

 insoluble in nitric acid, but soluble in ammonia, and blackening in the 

 Ugh?, or more quickhj in the sun, see 108. Solutions of lead and mer- 

 cury also detect muriatic salts, but pure chlorates are not affected by 

 these tests. See 70 b, and 83 b. 



a. The precipitate by nitrate of silver is not decomposed at a red heat: 

 but it melts, and upon cooling forms a crystalline, sometimes translu- 

 cent mass, which cuts somewhat like horn, from v. hich it has been call- 

 ed horn-silver : it is the lunar caustic of the apothecary, which is 

 soluble in water, and is then a proper test for muriatic acid. 



48. CHROMIUM, or chromic acid, is detected by proto-nitrate of 



mercury which forms a red precipitate becoming green when strongly 

 heated: al»o by hydro-sulphuret of ammonia, and prussiate of potass, 

 both of which produce green precipitates. Rose says, prussiate of 

 potass produces no precipitate. Nitrate of silver produces a carmine 

 colour changing to purple, and nitrate of copper a chestnut red. See 

 the tables of re-agents. 



a. The salts of chromic acid are precipitated by salts of lead of 

 a yellow colour : by salts of silver of a reddish browm j by protoxide 

 salts of mercury of an orange colour, and this precipitate heated leaves 

 protoxide of chromium. Salts of baryta produce a lemon-yellow pre- 

 cipitate. When mixed with a little alcohol and nitric acid, chromic acid, 



