On the Component Parts of Iron-Jtones. 201 



tcnlains, capable of afTuming the aeriform ftate by the com- 

 bination of caloric. This operation ought to be performed 

 in a progreffive heat, always fhort of fufion, The water is 

 then flowly evaporated without being decompoieti >, the ca- 

 loric unites to the carbonic acid, which foon affumes the 

 gafeous ftate ; and laftly, the fulphur, if any, fublimates. 



This procefs is eflentially neceflary to be performed before 

 the iron-ftone is introduced into the blaft-fumace. Were 

 raw iron-ftone, or ore, precipitated in the violent heat of 

 the fmel ting- furnace, the water and acid would inftantlybe 

 decompofed; the oxygen would partly unite to the iron in 

 addition to the fixed quantity peculiar to each ore, and part 

 of it wouid oxygenate the fulphur, either of the ore, or of 

 the pit-coal, a portion of which is always prefent in the 

 furnace. The whole mafs would then be precipitated in 

 fufion, and a dark porous lava obtained, containing iron 

 more difficult to be revived than ever, owing to the oreat 

 quantity of oxygen combined with it. In cafes of this kind, 

 the difengaged hydrogen manifefts its efcape, by changing 

 the colour of the flame from a mellow white to a pale fickly 

 blue. 



It muft from all this appear obvious, that, when torre- 

 facbon has been properly conducted, a very considerable part 

 by weight of the whole will be difiipated : the abfence of 

 thefe volatile fubftances always leaves the iron-ftones more 

 or lefs magnetic. The lofs of weight, however, is very dif- 

 ferent in the various claffes of iron-ftones, even when they 

 arc all expofed for the fame length of time to a degree of 

 heat capable of expelling thofe mixtures, which, under fuch, 

 circumftances, aflumc the gafeous ftate. 



I. Calcareous iron-ftone, when properly expofqd to tor- 

 refa&ion, lofes more of its weight than either of the other 

 two claffes. Where the lime is abundant, I have found this 

 iron ftonc lofe 38 per cent. bu{ more commonly 3$ and 36 

 per cent, of water, carbonic acid, and fulphur. 



3. Ar- 



