INTRODUCTION. 13 



Now it is interesting in the first place to notice that 

 many of these substances can be obtained from the 

 products of the rotting, or decomposition of wood, such 

 as goes on in bogs and in the soil; and, in the second, 

 that it is just these bodies which we obtain when coal 

 is heated — and we know that coal is practically nothing 

 but wood long bottled up in the earth. 



The other moiety of our piece of wood will be 

 found in the form of a much shrunken, but very perfect 

 model of the original specimen, and black in colour : in 

 fact, as a piece of charcoal. It is very interesting to 

 notice that it may show all the essential structural 

 peculiarities of the wood so distinctly, that it is even 

 possible to recognise the species of wood by means of 

 the microscope. 



These facts gain in importance when you learn that 

 it is frequently not difficult to make out the characters 

 of fossil woods, and I have had opportunities of satis- 

 fying myself that pieces of various species of timber, 

 buried for ages in the earth, show sufficient of their 

 structure, not only to enable one to determine what tree 

 yielded them, but even to show the marks of injury 

 done to them by parasitic fungi, as well as the parasites 

 themselves in their interior. I have also had occasion 

 to examine pieces of charcoal from the remains of an old 

 Roman funeral-pyre, or other fire, the structure of which 

 was quite recognisable. In all these cases the black 

 " carbonised " wood invites comparison with what we 

 know of coal — which is, in principle, indeed nothing else. 



The lump of charcoal, representing about half the 

 weight of the dry wood, will be found to consist almost 

 entirely of carbon : I say almost entirely, because a small 

 proportion of it will be found to be a mixture of several 

 mineral substances or salts, comprising what is known 



