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longer, as when the fires are made up at night, this 

 may be readily accomplished by putting a row of the 

 thick square paving tiles on the top of the whole 

 length of the flue, an hour or two before the houses 

 are finally closed. 



Flues are best built of bricks set on 

 their edges, and the top formed of a 

 shallow iron trough for the purpose of 

 holding water, and thus keeping the air 

 moist as required. At night, for retain- 

 ing heat, pantiles may be placed along 

 within the trough. The best form is the annexed. 



Hot Water in Tanks. — It is a law of fluids that 

 their hottest portions rise to the surface of the con- 

 taining vessel, and the coldest portions as invariably 

 subside to the lowest surface, because heat makes 

 them expand, and consequently diminishes their spe- 

 cific gravity ; and the abstraction of heat makes them 

 contract, and as consequently increase that gravity. 

 "When the boiler and tank are filled with water, as 

 well as their connecting pipes, and a fire is lighted, 

 the hottest portions rise to the top, flow along the 

 surface, and getting cool, sink to its bottom, and 

 passing downward enter again at the lower part, to 

 he once more heated, and pass through the same cir- 

 culatory system. A very small boiler will speedily 

 raise the heat of the water, in a very large tank, to 

 180 degs. ; and if this heat be imparted late in the 



