90 ON CAMBIUM. 



Caroline. I should think the wood, which burns so 

 well because it consists almost wholly of charcoal. 



Emily, And yet the leaves in which the carbon is de- 

 posited, when separated from the oxygen, should con- 

 tain more of that ingredient than the wood. 



Caroline. In that case leaves should be used for fuel 

 in preference to wood. 



Mrs. B. Emily is right : the green parts of plants 

 contain the most carbon ; and dry leaves make an excel- 

 lent combustible, but they are too large in volume to 

 form a convenient one. 



After the leaves, the bark, especially when green, 

 abounds most with carbon ; and, lastly, the wood : the 

 alburnum or white wood contains the least. 



Caroline. Green wood then should be most combus- 

 tible ; and yet it is noted for burning badly. 



Mrs. B. By green wood is commonly meant wood 

 not sufficiently dried. Whatever quantity of carbon wood 

 contains, it cannot prove a good combustible, unless the 

 water, and other juices injurious to combustion, first be 

 evaporated. 



The alburnum, when well dried, burns briskly, because 

 it contains a greater quantity of hydrogen than perfect 

 wood; and it is the combustion of hydrogen, you may 

 recollect, which produces flame : but, owing to its defi- 

 ciency of carbon, alburnum gives out less heat. 



The ascending sap, we have observed, contains also a 

 great variety of earthy and alkaline particles ; such as 

 magnesia, lime, silex, potash, and soda. When the 

 evaporation from the leaves takes place, these bodies are 

 deposited, and become constituent parts of the cambium, 

 and are thus conveyed to their several destinations. 



The most soluble of the earthy salts such as lime and 

 magnesia, are naturally most abundant in the sap ; and 

 when a plant is burnt, the earths, being incombustible, 

 form the materials which constitute its ashes. 



The alkaline salts, potash and soda, being also of a 

 soluble nature, are conveyed in considerable quantities 



489.^-Which parts of plants contain most carbon 1 ? 490. Which 

 next; and which least! 491. When will wood become a good com- 

 bustible! 492. Why does alburnum burn so well! 493. What ig 

 said of the alkaline particles with which sap is impregnited! 494. What 

 earthy salts in wood constitute its ashes when burnt! 



