INTRODUCTION. 15 



And j3. Incombustible constituents, or "ash," com- 

 prising salts of lime, potash, and a few other elements, 

 forming in all only something like from one to two per 

 cent, of the total weight of the piece of wood. 



But it is evident that such analyses as the above 

 would throw little light on the question, in what form 

 are these chemical elements and compounds present in 

 the intact wood ? And I shall have to pass over any 

 reference to the methods by which the chemist would 

 proceed in his further examination of the piece of woojd, 

 and content myself with the following brief summary. 



Mention has already been made as to the water which 

 is expelled on drying, and we have seen that nearly 

 50 per cent, by weight of the dry wood was carbon, 

 chiefly in the form of a charcoal skeleton of the structure. 

 Before the application of the intense heat of his com- 

 bustion apparatus, however, the chemist would find that 

 this structural part was composed of peculiar substances 

 known as cellulose and lignin, both of which consist of 

 carbon, hydrogen, and oxygen, combined in different pro- 

 portions ; the destruction of these substances it is which 

 yields the greater part of the carbon compounds referred 

 to above. 



Careful examination would also show that starch is 

 present in our piece of wood, and that in quantities which 

 vary greatly according to the season and the age of the 

 wood ; in the winter the percentage weight of starch 

 would be considerable, whereas in summer there would 

 be very little. 



5. BY THE PHYSICIST. 



Examined as a physical object, and by means of the 

 methods devised for measuring and weighing accurately. 



