and Iron-Stones ly Fujion. 187 



dency which individual ores have to afford their metal car- 

 bonat 'd, pofleffing ftrength, or otherwife, a flux of a me- 

 dium proportion of calcareous earth and glafs is determined 

 upon ; fuch as, with an iron-ftone of that genus, would af- 

 ford fuper-carbonatcd crude iron. Let the button of iron fo 

 obtained be the ftandard whereby to judge of fucceeding 

 refults ; and let all the ores belonging to the fame mine, or 

 ufed at the fame work, be compared with it : thefe will be 

 found, according to their mixtures, pofleffing different de- 

 grees of carbonation ; fome of them white in the frafture^ 

 and others again as richly carbonated as the ftandard regu- 

 lus ; their decrrees of ftrength alfo approaching or receding 

 from the ftandard as they approximate or vary from the na- 

 ture and proportion of its original mixture. 



To complete fuch an undertaking with accuracy, requires 

 a minute knowledge of the operations of the aflay-furnace, 

 and the degree of heat from time to time excited : the quan- 

 tity of ore in fuch a chain of experiments fliould be at all 

 limes the fame, and the requifite heat conveyed and com- 

 pleted a,t fimilar ftages of fufion and of feparation. Strict 



fircngth to the metal, yet I have not ventured a conjefture how far and 

 in what manner the mechanical ftrufture of the metal is altered when 

 additional ftrength is thus obtained. It will be a difficult matter to de- 

 cide, whether it is derived from the natural infufibility of the clay, by 

 preventing feparation for a longer time, and new modifying the ftrufture 

 of the particles of metal; or whether the acquired ftrength is entirely owing 

 to the molcculas of the metal becoming more flattened and tenacious by a 

 varied ftnge of cryftallifation. Moft probably it is owing to both caufes, 

 tgid that the former is pioduftive of the latter ; the one the caufe, and the 

 pther the cffcdt accounted for. 



We find, that from fiiiceous iron-ftone, which is fufed with the grcateft 

 facility, iron is obtained uncommonly white and brittle ; and again, from 

 pure calcareous iron-ftones, which are ftill more difficult to reduce than 

 the other two claffcf , we fmd an oppofite extreme of brittlcncfs, arifmg from 

 an extra combination of carbon, which deftroys the continuity of the par- 

 ticles to each other. Clay ftill holds the medium ; and its addition alone 

 rtflorcs a juft tejuilibrium, not of ftrength only, but of fufibility. 



^ accuracy 



