\'0L. LXXXir.] PHILOSOPHICAL TRANSACTIONS. 213 



tion as to absorption. One principal difficulty, as it appears to me, in the ma- 

 nufacture of iron, is to get rid of the charcoal. The oxygene readily enough 

 unites with a small portion; but the attraction of the iron on the one hand, and on 

 the other, the little disposition of the charcoal to put on the elastic form, in 

 comparison with many other less fixed substances, together form a very con- 

 siderable obstacle to the change of charcoal into air ; and, as I have already 

 observed, the iron probably holds the charcoal more strongly as its quantity 

 diminishes. In this state of things a small additional impediment will prevent 

 the heat from throwing the charcoal into the state of air ; and some degree of 

 pressure must be adequate to this effect : and why may not this point, from 

 which as you recede on opposite sides, the attraction of the particles of charcoal 

 for each other, or for iron, either shall or shall not be overcome by heat, have 

 been found in these experiments ? The next consideration will both illustrate and 

 confirm these ideas. 



3. A chemist, whose notions of iron are derived principally from books, and 

 from the phenomena which are presented by processes not having metallurgy for 

 their immediate object, will be apt to consider some things related above as in- 

 consistent : the violence of the heat, for instance, and the smalliiess of its 

 effects ; since even cast iron was not fused in all the experiments. The fact is, 

 when cast iron exposes a large surface, and heat is gradually applied, it proves 

 almost as infusible as malleable iron : indeed, by the gradual action of heat it is 

 converted, superficially at least, into malleable iron, or approximates towards it : 

 and considering only iron and charcoal, I believe, the fusibility of iron will be 

 directly as the quantity of charcoal it contains. Now in the experiments I have 

 described, pieces of ], 2, and 3 drachms, and sometimes less, were used, for 

 larger could not be inserted into the neck, of the retort. And, in order to avoid 

 this inconvenience in future, I would recommend cylinders to be cast, of a dia- 

 meter suited to the mouths of the vessels. This infusible coat would be an 

 impediment to the conversion of the parts below, by pressing on them ; the 

 elastic fluids could not either traverse the solid surface so freely as a liquid, and 

 perhaps, as I am disposed to believe, they could not traverse it at all. The 

 malleable skin seems close in its texture, and the porosity of the rest might 

 arise from the generation of just air enough to produce an internal expansion. 

 In the puddling operation, it is of the most material consequence to keep the 

 mass in constant agitation. Thus the parts are thoroughly blended, the attrac- 

 tion of cohesion is a good deal counteracted, and there can be no pieces hide- 

 bound, if I may so express myself. This last perhaps is the greatest advantage 

 derived from the labour of the workman. 



4. I was asked by one of the most ingenious and profound philosophers of the 

 present age, why I had neglected the action of the atmospheric air in the theory 



