Maclaurik. — A Bajnd Method of estimating Iron in Iron-ores. 51 



asbestos, and heated to redness by a long flat burner.^ The tube should 

 be from 15 in. to 18 in. long, and about J in. in diameter, reduced to \ in. 

 or less for 4 in. or 5 in., to allow of the ready deposition of antimony and 

 arsenic. It is interposed between the source of hydrogen and the hard 

 glass bulb tube in which reduction of the ore takes place. This treatment 

 removes all but minute traces of arsenic and antimony, and these may be 

 got rid of by passing the hydrogen through one or two wash-bottles con- 

 taining glass wool saturated with chromic acid. 



Using this method we got the results given in column A of the following 

 table. Those shown under B were obtained from the same solution in the 

 following manner. After titrating with permanganate (for A determina- 

 tions) the solutions were reduced by hydrogen sulphide (Hillebrand's 

 method), the excess of H2S removed by CO 2, and again titrated with per- 

 manganate. The results so obtained are shown in column B. As a further 

 check on these figures, the ore was fused with sodium and potassium car- 

 bonates, dissolved in sulphuric acid, reduced by means of sulphuretted 

 hydrogen, &c., as before, and titrated with potassium permanganate, the 

 percentages of iron so found being shown in column C. Or it was fused as 

 before, dissolved in hydrochloric acid, reduced by stannous chloride, and 

 titrated with bichromate, the results being shown in column D. 



These figures are sufficient to show that our method gives very satis- 

 factory results for such refractory ores as magnetites and ilmenites. For 

 these ores it has the further merit of making the estimation of titanium 

 quite a simple matter. This is done by adding hydrogen peroxide to the 

 solution after the permanganate titration, and estimating the percentage 

 of titanium by comparison with a standard solution of that substance. 

 By this means 9-12 per cent, of titanium dioxide was found in the Taranaki 

 magnetite, as against 9-27 per cent, obtained by fusion. Moreover, it was 

 found that none of the insoluble residues contained more than minute 

 traces of titanium. 



To recapitulate very briefly, the process consists of the following steps : — 



1. Roasting the finely ground ore. 



2. Reduction of the roasted ore by heating in coal-gas or hydrogen. 



3. Dissolution of the reduced ore in dilute sulphuric acid in an atmo- 

 sphere of carbon dioxide. 



4. Titration of the resulting solution by potassium permanganate. 

 The advantages of the process over those commonly employed are the 

 removal of any organic matter which might interfere with the subsecjuent 

 titration, the ease and completeness with which the ores are dissolved, the 

 accuracy of the titrations, and the possibility of estimating titanium in 

 the same solution. 



