Maclaurin. — A Bapid Method of esLimating Iron in Iron-ores. 49 



Art. XI. — A Rapid and Accurate Method uj estimating Iron in Iron-ores. 



By J. S. Maclaurin, D.Sc, F.C.S., and W. Donovax, M.Sc. 



[Bead before the Wellington PhUosophical Society, 2nd September, 1908.] 



Any one who has had experience in the estimation of iron in magnetites 

 and haematites must have frequently found difliculty in getting the iron 

 into solution within a reasonable time. Such difficulties led one of us to 

 subject the ore to a preliminary heating in hydrogen or coal-gas. The 

 iron could then be readily dissolved i!i hydrochloric acid, reduced by stannous 

 chloride, and estimated volumetrically. In these estimations, however, 

 potassium permanganate could not be used if really accurate results were 

 required, owing to the disturbing effect of hydrochloric acid, and conse- 

 quently one was driven to employ the bichromate method, which has the 

 serious defect of requiring an external indicator. These defects have been 

 entirely removed by modifying the process, which is now carried out in 

 the following manner : — 



A weighed quantity of finely ground ore is introduced into a hard glass 

 bulb tube by means of a small copper scoop (made of thick copper foil bent 

 into the desired shape and soldered to a stout piece of copper wire). Into 

 the ends of the tube, corks carrying narrow glass tubes are then fitted. 

 Should the ore contain organic matter, air is drawn through the tube by 

 means of a filter pump or aspirator, and the bulb heated to redness for a 

 few minutes, being gently rotated backwards and forwards during the 

 heating. It is then allowed to cool, the air-current stopped, and a stream 

 of hydrogen or coal-gas substituted. This is lighted at the exit end of the 

 small glass tube. Should hydrogen be used, the tube may be prevented 

 from closing up by the use of a platinum tip, made by rolling a small strip 

 of platinum foil round the end of the tube. After heating for from ten 

 to thirty minutes, according to the nature of the ore, the tube is allowed 

 to cool, the stream of hydrogen or coal-gas is shut ofi, and the reduced 

 ore shaken into a flask containing 1 or 2 grams of sodium bicarbonate and 

 a little water. Any ore remaining in the tube is washed into the flask 

 with dilute sulphuric acid. By this means sufficient carbon dioxide is 

 evolved to fill the flask, and so prevent oxidation of the iron. In order 

 to still further guard against oxidation, the flask is closed by a rubber cork 

 carrying a short exit-tube, and an inlet-tube which dips beneath the surface 

 of the solution in the flask, through which a steady stream of carbon dioxide 

 is allowed to flow from a Kipp's apparatus. The flask is then heated, and 

 the solution boiled for from five to twenty minutes, according to the ease 

 with which the iron dissolves. This operation requires little or no attention, 

 and can be carried out while another sample is being heated in the bulb 

 tube. 



When it is seen that all the iron is dissolved, the solution is allowed to 

 cool in the air, or more rapidly by closing the exit-tube with the finger, 

 and allowing water to flow over the outside of the flask, the carbon dioxide 

 apparatus being still, of course, attached. It only remains to shut off the 

 carbon dioxide, remove the cork from the flask, wash the tubes with a 

 little water, and titrate the solution with potassium permanganate. 



