Chemical Composition of Chromite. 283 



tion of other chromite mines but little light has been thrown 

 on this point. 



The chromite would be concentrated near the borders of the 

 peridotite in rounded masses, with offshoots penetrating into 

 the peridotite. The line of contact near the gneiss would be 

 sharp and nearly regular, while with the peridodite the con- 

 tact would be very irregular. 



In prospecting for either chromite or corundum the largest 

 and richest deposits may be expected near the contact of the 

 peridotite with the gneiss or other country rock. 



Chemical composition. — Chromite has been analyzed from 

 the following localities in North Carolina : Price's Creek, six 

 miles southwest of Burnesville, Yancey County ; Webster, 

 Jackson County ; and Corundum Hill, Macon County. 



Pure material for analysis, showing no impurities when 

 examined with the microscope, was readily obtained by hand 

 picking. 



The mineral was fused several times with bisulphate of 

 potash, then taken up with hydrochloric acid and silica tested 

 for. Iron, aluminium and chromium were precipitated with 

 ammonia, the precipitation being made at least three times. 

 Magnesium, calcium and manganese were determined in the 

 filtrates by the usual methods. 



The precipitate of the mixed oxides was dissolved in hydro- 

 chloric or nitric acid and the excess of acid evaporated. Sodium 

 hydroxide was then added in excess and chlorine passed into the 

 hot solution. The solution Was acidified and the iron and 

 aluminium precipitated twice with ammonia and weighed as 

 mixed oxides. These mixed oxides containing a trace of 

 chromium were fused with acid potassium sulphate, digested 

 with water and acidified. One precipitation was made with 

 ammonia to partially remove sulphates. This precipitate was 

 dissolved in hydrochloric acid and treated as before, the iron 

 and aluminium being obtained free from chromium. The iron 

 was determined volumetrically. 



To the filtrates containing the chromium, alcohol and hydro- 

 chloric acid were added and the solution digested for some 

 time. The chromium was precipitated as hydroxide and 

 weighed as Cr 2 G 3 . To ensure the purity of the precipitate, it 

 was fused with four parts of sodium carbonate to one part of 

 potassium nitrate, the fusion taken up with water and tested 

 for magnesium. 



A number of experiments were made to determine the ratio 

 of ferric to ferrous oxide, but they were all unsatisfactory. By 

 digesting the very finely powdered mineral in a mixture of hot 

 concentrated hydrofluoric and sulphuric acid, in an atmosphere 

 of carbon dioxide for half an hour, enough of the mineral was 

 decomposed to show the presence of ferric oxide. 



