272 On cerlam Products ohlained 



tinued red lieat, after which it left an oxide or rather a carbonat 

 of iron, such as remains from the combustion of plumbago. It 

 is in fact to be considered as an artificial plumbago, a substance 

 of whose nature all the charcoals of difiicult combustibility par- 

 take, deriving their resemblance apparently from the same cause. 



The formation of this plumbaginous substance serves to show 

 a very powerfid affinity between iron and carbon, even where the 

 proportions are very dift'crent from those which enter into the 

 composition of steel. But to effect this combination, it is neces- 

 sary that tlie carbon be in a state of previous union with other 

 substances, and that it be applied to the iron in that state. It 

 .will be in vain that we attempt to combine iron with charcoal 

 for this end, unless the charcoal or carbon be in that state of very 

 minute division in which it exists when precipitated by a new 

 affinity frona some previous combination. 



It is necessary now to account for the iron in this compound. 



This distillation of wood for charcoal is carried on in iron ves- 

 sels, and hence is derived the iron which enters into the com- 

 position of the pitch. I will not say that it is solely derived thence, 

 as it is probable that if there were iron containcfl in the vegeta- 

 ble matter, it would also be found in the same place. When the 

 acetic acid has been separated the iron remains united to the 

 pitch. This fact may show us, that if in the destructive analysis 

 of vegetable (and probably animal) matter, we trust to find the 

 iron they may contain in the residual matter of the distillation, 

 we may be dibappointed, since it may be carried over, together 

 with the substances I have now been describing, in the act of 

 ebullition, as happens in tliis very case, its tendency being to 

 combine with them, in preference to the ciiarcoal. 



As it was no part of my design to examine the vegetable ele- 

 ments, I did not pursue any experiments with this substance di- 

 stilled in earthen vessels so to ascertain whether in tliis case also 

 it would contain iron, l>ut I did enough to satisfy- myself that 

 the pitch was essentially the same in whichever way produced. 



It is already known that a substance resembling plumbago is 

 formed in water, it having been discovered by Fabroni in the 

 comitry round Naples. It is equally known to be formed in the 

 iron foundries; and the advocates for the igneous origin of coal 

 have also contended for that of plumbago, and h?ve supposed it 

 to have been produced by the contact of melted greenstone with 

 beds of coal. But even if we admit this cause of its formation, 

 something else seems necessary for the production of the sub- 

 stance, and some other mode of applying the heat reciuired be- 

 fore it can be produced. Nor indeed does the explanation suf- 

 ficiently qorrcsj;ond with the general geological po'^ition of plum-t 

 bago, 



