44: ' MAGNETITE. 



ted hydrogen. The reduction must be effected at the 

 highest temperature of the gas-lamp, for otherwise 

 the reduced iron, even when cool, may reoxidize and 

 sometimes inflame in the air. It is safer to reduce the 

 oxide in a small porcelain boat, placed in a tube of 

 porcelain, which is heated by a charcoal fire, or over 

 the gas furnace. 



The reduced iron is heated in a stream of hydro- 

 chloric acid gas. Silicic acid, which is often contained 

 in limonite, is then left undissolved, and may be 

 weighed. 



24. MAGNETITE.* 

 FeO, Fe 2 O 3 . 



To determine the amount of oxygen which is com- 

 bined with the iron, the proto-sesquioxide is reduced 

 by hydrogen, as in No. 23. 



" If the substance contain only proto-sesquioxide of 

 iron, the whole of the iron may be determined by dis- 

 solving in hydrochloric acid, heating with some chlo- 

 rate of potassa, to convert all the protochloride into 

 sesquichloride, and adding ammonia to precipitate the 

 sesquioxide of iron, which is washed, dried, ignited, 

 and weighed. 



If other constituents be present the total amount of 

 iron may be determined as follows: The substance is 

 dissolved in an excess of hydrochloric acid, the proto- 

 chloride converted into sesquichloride by addition of 

 chlorate of potassa, and all free chlorine expelled by- 

 boiling. The solution is then diluted with water until 

 the flask is more than half-full; a weighed strip of 

 bright sheet-copper is placed in the solution, the flask 

 closed by a cork furnished with a narrow glass tube, 



* Forge-scales have a similar composition. 



