f?00 On the Affinities of Earths for Carlun. 



affords any carbon to iron in fusion, I was forced to seek a 

 new theory. 



I had often remarked that, in forming crucibles, a mix- 

 ture of plumbago, charcoal, or coke-dust, while it conferred 

 a degree of toughness to the clay in the act of heating, and 

 presented what is by workmen called clinking, uniformly 

 created a degree of fusibility beyond the natural tendency of 

 the clay when unmixed. It occurred to me that this fusi- 

 bility might proceed from a chemical atr.nitv being excited 

 by the clay upon the carbonaceous matter of the addition 

 in very high temperatures, and that something similar taking 

 place betwixt the earths and the carbon in the blast-furnace, 

 might tend to explain, in a satisfactory manner, the phaeno- 

 mena of the ditlevent iron-stones. 



I immediately considered lime, clay, and silex, in some 

 respects in the same state as the metallic oxides, and parti- 

 cularly similar to the one with which they were united in 

 their earthy state ; each of them separating from the com- 

 mon mass, according to their atiinitics, portions of the car- 

 bonaceous matter of the fuel, and either with it becoming 

 a binary compound, or by discharging it in the state of an 

 elastic vapour. 



From this theory it seemed consonant with the practical 

 remarks formerly made to deduce, that the fact of calca- 

 reous matter in the blast-furnace, and particularly in union 

 with iron-stones, forming iron more carbonated than argil- 

 laceous or siliceous ores, might arise from a less degree of 

 affinity subsisting betwixt calcareous earth and carbon, than 

 between the others and that substance : or that, in other 

 \vords, lime not absorbing at all, or in very small quantities, 

 the carbon of the fuel, a larger portion was left to be united 

 with the iron; and hence followed an easy explanation of 

 its tendency to form carburated or " sulphury iron." 



As the products of carbonation diminish by the increase 

 of clay, I immediately inferred that clay absorbed a larsjer 

 portion of carbon than lime, and this robbed the iron of a 

 portion of its coaly principle. The same reasoning I ap- 

 plied to siliceous iron-stones, but in an extent proportioned 

 to the excessive decarbonation of the metal when these 

 iron-stones are used in quantity. 



As all theory, however, seemed objectionable that was 

 not founded upon direct experiment, particularly when the 

 elementary principles could be subjected with ease to their 

 supposed respective affinities, I determined to engac^e in an 

 undertaking", which, though it at first sight appeared labo- 

 rious, promised a rich and an abundant har\-est. 



The 



