42 HEMATITE. L1MONITE. 



into protoxide. The solution is boiled till it no longer 

 smells of sulphurous acid, neutralized with carbonate 

 of soda, and, in order to produce a little sesquioxide 

 of iron, mixed with a very little chlorine- water, the 

 quantity of which must be regulated according to the 

 amount of phosphoric acid which is present. The 

 solution must now be mixed with an excess of acetate 

 of soda, when phosphate of sesquioxide of iron sepa- 

 rates as a white precipitate. Chlorine- water is then 

 added, drop by drop, until the liquid has assumed a 

 reddish color, when it is boiled, so that the precipitate 

 may collect, and be filtered. From this precipitate 

 the phosphoric acid is separated by sulphide of ammo- 

 nium, as directed above. 



Or it may be dissolved in hydrochloric acid, boiled 

 with sulphite of soda, and afterwards with excess of 

 caustic soda, till the precipitate is converted into black 

 proto-sesquioxide of iron, which is filtered off. The 

 solution is acidified, and the phosphoric acid precipi- 

 tated as above. 



23. HEMATITE, Fe 2 3 , AND LTMONITE, Fe 2 O 3 , 3 HO. 



For the determination of the water, weighed frag- 

 ments of the ore are heated to redness, for a long time, 

 in a platinum crucible. If the mineral decrepitates, 

 it must first be finely powdered. 



In order to determine the oxygen, the fragments of 

 ignited limonite or of hematite are heated to redness 

 in a weighed bulb-tube of very infusible glass (the 

 bulb being as small as possible), through which a 

 stream of dry hydrogen, free from arsenic, is transmit- 

 ted as long as any water is formed. 



In order to purify hydrogen it is passed through the 

 U tubes containing pumice or fragments of porcelain 



