IRON 1027 



tion of caustic potash, specific gravity 1'27, in a silver dish; the silica which existed 

 in the iron in the form of silicon is hereby dissolved ; the clear caustic solution is 

 drawn off by a pipe or siphon, and the black residue repeatedly washed ; it is dried 

 at as high a temperature as it will bear, and weighed ; it is then heated to redness in 

 a current of air, until the whole of the carbon is burnt off. A reddish residue gene- 

 rally remains, which is weighed, and the weight deducted from that of original black 

 residue, the difference gives the amount of graphite. 



3. Silicon. The amount of this element is determined by evaporating to dry ness 

 a hydrochloric solution of a weighed quantity of the metal : the dry residue is re- 

 digested with hydrochloric acid, diluted with water, boiled and filtered ; the insoluble 

 matter on the filter is washed, dried, and ignited, until the whole of the carbon is 

 boiled off; it is then weighed, after which it is digested with solution of potash, and the 

 residue, if any, washed, dried, ignited, and weighed : the difference between the two 

 weights gives the amount of silicic acid, 100 parts of which indicate 47 parts of silicon. 



4. Phosphorus. A weighed portion of the metal is digested in nitro-hydrochloric acid, 

 evaporated to dryness, and the residue redigested with hydrochloric acid. The solution 

 is treated precisely as recommended for the determination of phosphoric acid in ores ; 

 every 100 parts of pyrophosphate of magnesia indicate 28'56 parts of phosphorus. 



5. Sulphur. In grey iron this element is very conveniently and accurately estimated 

 by allowing the gas evolved by the action of hydrochloric acid on a weighed quantity 

 ^about 100 grains) of the metal, in filings or borings, to pass slowly through a solu- 

 tion of acetate of lead acidified by acetic acid : the sulphur, the whole of which takes 

 the form of sulphuretted hydrogen, enters into combination with the lead, forming a 

 black precipitate of sulphide of lead, which is collected, washed, and converted into 

 sulphate of lead by digesting it with nitric acid, evaporating to dryness, and gently 

 igniting: 100 parts sulphate of lead =10*55 sulphur. The most minute quantity of 

 sulphur in iron is detected by this process. If, however, crude white iron is under 

 examination, this method does not give satisfactory results, on account of the diffi- 

 culty with which it is acted upon by hydrochloric acid ; it is better, therefore, to treat 

 the metal with nitro-hydrochloric acid, evaporate to dryness, re-digest with hydro- 

 chloric acid, and then precipitate the filtered solution with great excess of chloride of 

 barium ; or the finely-divided metal may be fused in a gold crucible, with an equal 

 weight of pure nitrate of soda, and twice its weight of pure alkaline carbonates ; the 

 fused mass is extracted with water acidified with hydrochloric acid, and finally pre- 

 cipitated by chloride of barium. 



Manganese. This metal is determined by the process described for its estimation 

 in ores ; the iron must exist in the solution in the form of sesquioxide. 



Arsenic and Copper. The nitro-hydrochloric solution of the metal is evaporated 

 to dryness, re-digested with hydrochloric acid, and filtered. The iron in the clear 

 solution is reduced to protochloride by boiling with a sufficient quantity of sulphite 

 of ammonia, the solution is boiled till it has lost all smell of sulphurous acid. It is 

 then saturated with sulphuretted hydrogen, and allowed to stand for 24 hours in a 

 closed vessel, the excess of gas is boiled off, and the precipitate, if any, collected on a 

 small filter and well washed ; it is digested with monosulphide of potassium, which 

 dissolves the sulphide of arsenic, leaving the sulphide of copper untouched ; the latter 

 is decomposed by heating with nitric acid, and the presence of copper evinced by the 

 addition of ammonia, which produces a fine blue colour ; the sulphide of arsenic is 

 precipitated from its solution in sulphide of potassium by dilute sulphuric acid ; it 

 may be redissolved in aqua regia, and the nitric acid having been expelled by evapo- 

 ration, the arsenic may be reduced in Marsh's apparatus. 



Nickel and Cobalt. These metals, if present, will be found in the solution from which 

 the copper and arsenic have been precipitated by sulphuretted hydrogen. The solution 

 is peroxidised, and the sesquioxide of iron precipitated by slight excess of carbonate 

 of baryta, after which the nickel and cobalt are precipitated by sulphide of ammonium. 



Chromium and Vanadium These metals, which should be looked for in the car- 

 bonaceous residue obtained by dissolving a large quantity of the iron in dilute hydro- 

 chloric or sulphuric acid, are detected as follows ( Wbhler} : The ignited residue is 

 intimately mixed with one-third of its weight of nitre, and exposed for an hour in 

 a crucible to a gentle ignition. When cool, the mass is powdered and boiled with 

 water. The filtered solution is gradually mixed, and well stirred with nitric acid, 

 taking care that it may still remain slightly alkaline, and that no nitrous acid is 

 liberated which would reduce the vanadic and chromic acids. The solution is then 

 mixed with an excess of solution of chloride of barium as long as any precipitate is 

 produced. The precipitate, which consists of vanadate and chromate of baryta, is 

 decomposed with slight excess of dilute sulphuric acid, and filtered. The filtrate is 

 neutralised with ammonia, concentrated by evaporation, and a fragment of chloride of 

 ammonium placed in it. In proportion as the solution becomes saturated with chloride 



3u2 



