198 On the Component Tarts of Iron-Jlones. 



work to thofe who may wifti to attain a practical knowledge 

 of thefe ores, fo far as it relates to their manufacture. 



It is however eafy to counteract the natural tendency 

 which every iron-ftone has in this cafe, to afford its iron of a 

 certain quality, and to make each of them yield crude iron 

 of all the different degrees of fufibility and ftrength. Is it 

 not obvious, that fince the qualities of crude iron depend 

 upon the mixtures and their kinds compoiing the ftones, 

 that if nature be affifted by adding or fubtraCting from them 

 in the blaft-furnace, every quality of crude iron may be 

 produced from the fame iron-ftone ? I have feen moft of 

 thefe remits determined in the large way, and the whole of 

 them beautifully confirmed in the affay-mrnace. 



It remains with the prefent manufacturer to confider whe- 

 ther itwill be more his intereft to rejeCt fuch iron-ftones as are 

 of difficult carbonation, or to apply the neceffary additional 

 proportions of fuel, capable of correcting the quality of fili- 

 ceous iron-ftones. Not fo, however, to thofe who may at 

 fome future period fucceed him j neceffity, at all times inge- 

 nious, affifted by the increafing light which fcience daily 

 fheds over our manufactures, will devife the means of calling 

 into profitable exiftence the metal contained in all thofe 

 ores which may have fallen into difrepute in the prefent 

 day, or from which at this time it is thought impracticable 

 to extraCt metal in the large way. 



The ufual criterions by which iron-ftone is judged, whe- 

 ther it be fufficiently rich in iron for the purpofe of fmelting, 

 are the following : 



1 . The degree of tenacity with which it adheres, to the 

 tongue after torrefaCtion : 2. Its colour: 3. The obedience 

 to the magnet when pulverifed : 4. By depriving of its iron 

 a given weight of the ore, in contaCt with charcoal and fu- 

 Jible earths in the affay-furnace. 



The firft and third of thefe methods are liable to great 

 error,, The adhefion to the tongue will be more in propor- 

 tion 



