TIMBER AND TIMBER TREES. 



the water of the " sap," as it is called, held by capillarity 

 in the visible cavities of the wood ; but the second lot 

 of water was present in the substance of the walls of 

 those cavities, not as movable liquid water, but as what 

 we know as " imbibed " water, and it was held fast 

 between the structural units of those walls by molecular 

 forces of another category. 



Having determined that the piece of wood contained 

 (in whatever form) so much water, the chemist would 

 then proceed to analyse the solid, dry portion, of known 

 weight, which remains. 



This he would do by burning it under conditions 

 which he would be able to control. Here, again, he 

 ■could advance in stages. If he chose^ he might first 

 simply raise the temperature, gradually, but far beyond 

 the drying points already referred to, and so distil off as 

 much as could be thus got rid of ; he would then examine 

 the products, and would find some curious and interest- 

 ing results. 



Put shortly, about one-half of the substance of the 

 dry wood will be eventually distilled off in the form of 

 gases and vapours, while the other half will remain 

 behind in a solid form. 



The gases which escape will consist of Carbon 

 dioxide, carbonic oxide. Marsh-gas, and certain other 

 gaseous compounds of the elements Carbon and Hydro- 

 gen. 



The more liquid bodies will contain certain com- 

 pounds of Carbon, with Hydrogen, or with that element 

 and Oxygen, of the nature of Alcohol, Vinegar, and such 

 like substances. Benzol, Xylol, Creosote, and a number 

 of other queer compounds, as well as Ammonia. More- 

 over, many of these substances will be mixed in a brown 

 or black viscid mess, which is in fact "tar." 



