Olf SPARRY IRON ORES. 



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diminish the fusibility of iron ores; at least if this cohesion therefore not 

 can be estimated by the harclncss of the ore, and the resis- gjon. ' 

 tance it offers to the action of acids, for none possess these 

 two qualities in a more striking degree than the iron crystals 

 of the isle of Elba. The committee are of a similar opinion, 

 only the fusion must requife so much lousier time in pro- 

 portion as the ore is in frag^ments of a larger bulk, 



' 'Mr.'DescOtils could have wished to analyse specimens of 

 i^fractory iron "spar coin pari tively with specimens of th6 

 same ore become fusible by exposure to the air: bat not hav- 

 ini^been able to procure any, he thought he might supply 

 their place by two pieces from the same vein, one of which 

 was not altered, the otheir had passed to the state of a free 

 ore. 



Without describing the method be employed for this pur- 'But tomagn*;. 

 pose, which we' Consider as very accurate, we shall only say, *^^' 

 tiiat be found the dtx!omposed ore no longer contained any 

 magnesia or carbonic acid, while the other contained four per 

 cent of carbonic acid and magnesia. 



The analysis of live other specimens of free ores, from Farther proofs, 

 different places, gave him the same results, whence he con- 

 cludes, that the separation of the magnesia is complete when 

 the decomposition of the ores is complete. 



In some cases he suspects^ that it is to the efflorescence of Modeinwhick 

 the pyrites, from which scarcely any spai-ry iron ore is free, the magnesia. 

 that the solution and abstraction of the magnesia of the raw ^^ ^^^^'^ ; , 

 ore is owing; since sulphate of magnesia is sometimes to be 

 observed on heaps of ore of an analogous nature exposed to 

 the air, as well as in the waters with which these ores are 

 washed ; and he has obtained similar results in a small way, 

 by putting magnesian iron spar in powder, into a solution of 

 sulphate of iron. 



He believes however, that it is most frequently the carbo- Action of car- 

 nic acid, which, disengaged from the iron in proportion as 

 this absorbs oxigen, dissolves and carries ofl" the magnesia by 

 means of watep, .1 



As to the change effected in the roasted ore by exposure Effect of roa^-* 

 to air and rain, the conjectures of Mr, Descotils are con- ing. 

 firmed by analysing the waters, with which a heap of roasted 

 ore long exposed to the air had been washed. These waters 



contained 



