30 



These calculations are all founded upon the suppo- 

 sition that the condensed water is returned to the 

 boiler whilst hot ; but if this cannot be effected, then 

 one twelfth more fuel will be required. The boiler 

 for the supply either of steam or hot water, should 

 be covered with the best available non-conductor of 

 heat ; and this is either charcoal or sand. 



A case of brickwork, with pulverized charcoal, be- 

 tween this and the boiler, is to be preferred to any- 

 other. A boiler having a surface of seventy feet ex- 

 posed to the air, in a temperature of 32 degs., requires 

 an extra bushel of coals to be consumed per day, to 

 compensate for the heat radiated and conducted from 

 that surface ; and the smaller the boiler, the greater is 

 the proportionate waste. The surface of the pipes 

 should be painted black, because a surface of this 

 colour gives out more heat in a given time than any 

 other. {Johnson's Principles of Gardening^) 



In heating by hot water there are some practical 

 questions which gardeners require to have answered, 

 but to do which neither the country ironmonger nor 

 country builder is usually qualified. One of these 

 questions very usually is, " How large ought the boiler 

 to be to keep these pipes hot?" Now, the total size 

 of the boiler really has nothing to do with the ques- 

 tion ; indeed, the smaller it is, the better, provided a 

 sufficient surface of it can be exposed to the fire. 



Mr. Hood furnishes the following useful table, 



