158 Economical Method of heating Flues of Forcing Houses. 



affords much more light and heat during combustion, than 

 an equal bulk of dry wood ; and I was long acquainted with 

 the circumstance before I was in any degree able to conjec- 

 ture the cause of it ; but I have subsequently attributed the 

 increased production of heat and light by the intermixture 

 of green and dry wood to the decomposition of water, the 

 oxygen of which readily combines with charcoal in a red 

 heat, whilst the hydrogen being disengaged, burns when it 

 comes into contact with the atmospheric air : and, upon 

 subjecting the experiment to the inspection of Sir Humphry 

 Davy and Mr. Pepys, they both agreed in attributing the 

 increased strength and brightness of the fire to the decom- 

 position of the water, which exhaled from the green wood. 



The mixture of coal dust and clay being always placed 

 upon the fire in a very wet state, necessarily discharges a 

 large quantity of water in the state of steam; part of which 

 condenses in the cooler parts of the flues ; where it is pro- 

 bably absorbed in considerable quantity by the bricks, and 

 exhaled into the house ; for I have often found the sides of 

 the flues to feel damp. My hot-house, therefore, though 

 apparently a dry stove, is not really such ; and possibly the 

 exhalation of moisture from the flues may be the cause why 

 my pine plants have thriven so much better in very high 

 temperature, than such plants are said to have usually done 

 in those forcing houses which are properly called dry stoves, 



