lochhead] CANADIAN DEPARTMENT 279 



It will be found, by holding the hand above the flame of the lamp, 

 that no charcoal issues from //—nor does it come out of the surround- 

 ing air. Hence it must have been in the stick at first. But why did 

 the charcoal not then make the stick black? 



Heat slowly and carefully a little dried wood, cut into small pieces 

 in the bottom of a closed test-tube. Clear drops of a tasteless liquid 

 like water form on the inside of the tube above the wood; and as the 

 water gathers, the charcoal appears. The water evidently comes out 

 of the dry wood and leaves the charcoal behind. 



It can easily be shown, by means of a hand balance, that a piece 

 of charcoal (from a stove) weighs less than a piece of the dry wood, 

 equal in size, from which the charcoal was obtained. 



It is plain then that dry white wood contains both charcoal and 

 water, and that when the water is driven out by the heat, the charcoal 

 can be seen. And so it appears that the wa'er in the wood hides the 

 charcoal, else the wood would look black, and the charcoal conceals 

 the water, else the wood would feel wet. 



Ic may now be stated that when two substances —as charcoal and 

 water in this case — are so united together that they conceal each 

 other's properties, the two substances are said to be chemically 

 united or combined; and the substance they form by their union is 

 called a chemical compound. Thus dry wood may be regarded as a 

 chemical compound of carbon and water. 



Next mix together, in a bottle, water and powdered charcoal. Do 

 they unite chemically? They do not conceal each other's properties. 

 The black charcoal can still be seen and the water felt. They now 

 form, not a chemical compound, but a mechanical or physical mix- 

 ture. But how can the charcoal and water be got to unite chemically ? 

 They must have been chemically separate before they united to form 

 wood; but we don't know, at present, how to compel them to com- 

 bine to form wood. 



Put finely divided wood, to the, depth of about an inch, into a test- 

 tube loosely closed with a cork or the thumb — and apply heat until 

 the tube is filled with smoky gas; then without withdrawing the heat 

 remove the cork or thumb, and try with a match until you succeed, 

 to set fire to the gas in the tube. How do you account for this com- 

 bustible "wood-gas"? Since this gas will burn, it cannot be water- 

 gas (steam); so we must conclude, since chemists find that pure wood 

 is composed entirely of carbon and water, that this gas was formed in 

 some way from these two substances in the wood. It should be noted 



