204: CAST IRON. 



tered from the precipitate produced by bicarbonate of 

 soda. (See No. 25.) 



IX. CHROMIUM AND VANADIUM. A large quantity 

 of the iron-filings is ignited with 2 parts of nitre and 1 

 part of carbonate of soda, the mass extracted with 

 water, and the solution treated as in No. 100, when 

 phosphoric and arsenic acids may likewise be sought. 

 It is safer to employ for this purpose the carbonaceous 

 residue obtained by dissolving a large quantity of the 

 iron in dilute sulphuric acid. 



X. MOLYBDENUM. Sometimes this metal is ex- 

 tracted, together with the arsenic, by sulphide of 

 ammonium, from the black carbonaceous residue; in 

 such a case, it is reprecipitated, together with the 

 pentasulphide of arsenic, an adding an acid to the 

 solution. If this precipitate be distilled in a tube, the 

 sulphide of molybdenum is left behind. 



If the cast-iron is rich in molybdenum, it is dis- 

 solved in aqua-regia and the molybdenum precipitated 

 by hydrosulphuric acid, placing in the acid solution 

 at the same time a piece of zinc, which renders the 

 precipitation complete. 



XL SULPHUR. The sulphur may be determined ap- 

 proximately by evolving it as sulphuretted hydrogen, 

 as in No. 1, when the iron is dissolved in dilute 

 sulphuric acid. Or it exists as sulphuric acid in the 

 solutions obtained at III. and VI., and may be precipi- 

 tated by chloride of barium. Or a large quantity of iron 

 may be dissolved in aqua-regia, and the sulphuric 

 acid formed may be precipitated from the diluted so- 

 lution by chloride of barium. 



XII. NICKEL AND COBALT may be detected in the 

 solution from which the copper has been removed by 

 sulphuretted hydrogen. This solution is r-eoxidized, 

 and the sesquioxide of iron precipitated by carbonate 

 of baryta, after which the nickel and cobalt are pre- 

 cipitated by sulphide of ammonium. 



