different Earths for Carbon. 49 



bling the coarsest lavas or cinders that come from the blast- 

 furnace. 



2d, From this circumstance I would endeavour to explain in 

 part a chief constituent in the scouring cinder of the blast-fur- 

 nace, not hitherto explicable upon common grounds. When 

 these circumstances unite to produce this cinder at the fur- 

 nace, it flows copiously of a black spongy texture, frequently 

 igniting sparks resembling the deflagration of carbon. The 

 quantity of iron, which has hitherto been deemed its colour- 

 ing principle^ seldom exceeds 3 percent., and always ap- 

 peared to me to be inadequate to explain the uncommon 

 appearance of the cinder. Upon the grounds of clay- ab- 

 sorbing carbon, it is easy to suppose, should any cir- 

 cumstance occur in the smelting process to establish an 

 extra share of affinity betwixt the argillaceous matter of the 

 ores and the carbon of the fuel, that a considerable portion 

 of the latter will unite to the former, and change the colour 

 and form of the lava. The crude iron then will become 

 decarbonated, as a consequence of this affinity. It will be 

 deprived of its necessary share of fuel, become inflammable, 

 and oxidate before the blast. The iron thus debased will 

 unite to the general current of lava, and account for the 

 portion of iron which such cinders generally contain. This 

 explanation is the reverse of what could be formerly ad- 

 vanced; for the scouring or running of a black porous 

 cinder could only be attributed to the combustion of the 

 iron by some more remote cause. 



3d, The affinity or tendency which carbon has to unite 

 with clay is so great, that l-300dth part of the former pro- 

 duces the most striking varieties in the result. In many 

 other experiments, not particularized here, I found that 

 even 1-SOOdth part of carbon produced an effect upon the 

 product, as to density, colour, and transparency. This 

 being the case, may' there not exist similar unsuspected 

 affinities betwixt iron and clay, and betwixt oxygen and 

 clay, even in the process of smelting ? and may not these 

 be productive of permanent effects upon the quality of the 

 manufactured iron ? 



4th, I had frequently occasion to notice, in the course of 

 performing these experiments, the strength of affinity ex- 

 isting betwixt carbon and the different clays. In one ex- 

 periment, wherein pure clay and carbon were exposed in a 

 Cornwall clay crucible with a Sturbridge clay cover, I re- 

 marked that the pure clay was equally so as when intro- 

 duced ; but the interior surface of the crucible was covered 

 with alight blue glaze, while the top of Sturbridge clay 



No. 73. June 1804. D was 



