in ^e Manufa3ure of Crude Iron,. 55 



frequently refolved into tranfparent cryftals : the chafmi 

 where thcfe are found are fometimes enriched with beautiful 

 prifniatic pvritical cryftals of a flat fcaly form. The com- 

 ponent parts of this Hme-ftone are as follow : Water of 

 cryftallifation and carbonic acid - - 39'52 



Siiex - - - . 5-73 



Lime - - - - 5475 



ICO parts. 



From what has been ftated, we are led to inquire into the 

 caufe which produces effe6ls fo widely different in the fufi- 

 bility and ftrength of crude iron. The exiilence of calcare- 

 ous, argillaceous and fiiiceous earths in the blaft furnace, has 

 been mentioned as eff'efting thefe changes; and it has been 

 alfo noticed that, under certain mixtures of thcfe, determinate 

 qualities of crude iron are produced. 



If a predominancy of calcareous earth is ufed as the 

 ftandard for comparifon, with a local proportion of fuel, we 

 find that in proportion as the lime is diminifhed in quantity, 

 and clay added through the medium of the ore, the quantity 

 of meta! produced will be lefs, but its ftrength greatly in- 

 creafcd ; and if the argillaceous ores are pure, the carbona- 

 tion of the metal will be little altered. Should fiiiceous 

 mixtures be applied in place of argillaceous, we find that, in 

 proportion as limedecreafes, and the quantity of fand in the 

 furnace is augmented, the quality of the iron becomes lefs 

 carbonated, lefs fufible, and its fmall portion of ftrength 

 greatly impaired : fand through the medium of the ore may 

 be added, fo as to render the iron as brittle as glafs, and a? 

 white in the fracture as filver. 



Again, let a predominancy of fiiiceous earths in the blaft 

 furnace be the ftandard for comparifon ; in proportion as thef« 

 are dlminiftied by the addition of argillaceous ores, the metal 

 will paf&from the ftate of extreme brittlenefs and oxygenation, 

 to a ftate comparatively ftrongerand containing more carbon, 

 {iliould calcareous iron ftones be added, their addition will 

 E 4 inauediatcly 



