8 Dr Macculloch on Black Lead from Cast-Iron, 



mon way of making charcoal in pits ; although that process is 

 always used in the gunpowder manufactories. It is for the same 

 reason that animal charcoal, or that of coal, will not make gun- 

 powder. Both of these are hard and brilliant ; and the former, 

 in particular, has sometimes a pseudo-metallic lustre, equal to 

 that of black-lead. The chain of analogy is thus extended 

 among all these substances : but it is time to terminate this com- 

 munication. I am, yours, &c. &c. 



J. MACCULLOCH. 



EDIN.BUKGH, July 



