112 METALLOSALINES. [IV. 



iron that may be present, milk of lime must be poured in and 

 the whole left to repose. The clear supernatant liquor will, 

 when drawn off, yield bichromate of potassa by double de- 

 composition. This mode is said to be more economical, in 

 time and expense, than the usual method wuth nitre *and pot- 

 ash, but we must doubt its feasibility. 



Tilghman's methods (Rep. Pat. Inv. 1847) differ materially 

 from the foregoing. One requires the ignition of the chromo- 

 ferrite with lime and powdered feldspar. The other proposes 

 its mixture with 2 pts. lime and 2 pts. sulphate of potassa, 

 and subsequent heating on a reverberatory hearth, in contact 

 with aqueous vapor. For the details of the ingenious pro- 

 cesses of this chemist, we refer to the original paper. 



A new Metal in Chrome-ore. — Ullgren (Vetensk Acad. 

 Forhand. 1850) has given an account of a substance noticed 

 in the chrome iron of Roros, and which he considers a new 

 metal. Its oxides bear a near analogy to those of iron. 



Double Chromates. — Schneitzer (Journ. fiir Prac. Chem. 

 xxxix.) has announced the existence of two double chromates. 

 They are both of a beautiful yellow tint, and crystallizable. 

 One, the chromate of potassa and magnesia, made by adding 

 calcined magnesia to a strong solution of bichromate of po- 

 tassa, heating and evaporating to crystallization, has the com- 

 position 2Cr03,KO,MgO-f2Aq. The other, chromate of 

 potassa and lime, has the formula 2Cr03,KO,CaO-f 2Aq. 



Oxide of Chrome. — Parian (Berz. Jahresb. 1846, 177) pre- 

 pares it by mixing 4 pts. bichromate of potassa wdth 1 pt. 

 starch, igniting it in a hessian crucible, extracting carbonate 

 of potassa by water, and again igniting the oxide of chrome. 

 If the chrome salt had been free from sulphuric acid, the oxide 

 will be a pure green. If it contain this acid, the salt is pu- 

 rified by crystallization. To test its presence, 1 pt. of the 

 salt is dissolved in water with 3 pts. tartaric acid until car- 

 bonic acid ceases to escape, the solution treated with muriatic 

 acid, and then tested with chloride of barium. 



Wittstein's method is to ignite for | an hour 19 pts. bi- 

 chromate of potassa and 4 pts. sulphur, to powder the mass 



