On Primary Ores of Iron. 353 



The form and appearance of the mafs of this ore much 

 fefembles the exceffively faturated i'peeimens of crude iron 

 and plumbago, defcribed in my paper upon the principles of 

 iron and fteel, with an allowance in the former for its long 

 expofure to the tarnifhing effects of water and other ele- 

 ments : the agency of thefe has conferred a variety of colours 

 in flowers, though the principal colouring of the ore feems to 

 have been the effects of oxygen combined with the iron at 

 certain degrees of heat : in its raw ftate the magnet has little 

 power over it. Of this ore pulverifed (which pofTeffed a line 

 reddifh brown colour, interfperfed with mining fpecula of 

 magnetic iron ore, refembling plumbago produced in the 

 fmelting furnace), I threw into an iron veflel heated to red- 

 nefs 80 grains : a gas was difengaged, which, from its fmeJl, 

 I concluded was carbonic acid gas, for I had not at hand a 

 proper apparatus or lime-water to try it with : the ore deep- 

 ened during ten minutes expofure, without changing the 

 fplcndor of the fmall fpecula; when cooled, it was found to 

 have loft 2 grains = 2 '25 per cent. 



I next introduced into a clofe veffelj in fmall pieces', 315 

 grains, and expofed them to torrefaclion for four hours in a 

 bright red heat : the refidue weighed 282 ; fo that there were 

 loft ot carbonic acid, and perhaps a little water, 33 grains = 

 lo - 7 per cent. The fine red, brown, and purple colours, 

 were now totally annihilated ; a flightly coloured powder was 

 attached to the Hopper of the veflel J the. ore was now of a 

 dull blndfti colour, much frittered, granulated, but not pul- 

 verulent: the magnet in this ftate pofleffed aconfiderable de- 

 gree of influence over it, but by no means in proportion to 

 the quantity of iron which it contained — *not even equal to 

 what it has on common iron'-ftones : from this circumftance 

 I inferred, that aconfiderable quantity of oxygen ftill remain- 

 ed fixed with the metal. In order to afcertain this, I intro- 

 duced the laft product, weighing 283 grainy into a clofe vef- 

 fel, mixed with charcoal duft : the mixture was expofed for 

 nearly ten hours to a bright red heat; the ore being then fe- 

 Vol. ill. A a parated. 



