234 PRINCIPLES OF GAEDENIKG. [CH. VII. 



of water per hour, to allow for unavoidable loss. In 

 the extreme case of the thermometer being at zero, 

 the consimiption of coals to keep up tliis evaporation 

 will be 12|lbs. per hour^. 



These calculations are all founded upon the sup- 

 position 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 ^^ith the best available non-con- 

 ductor of heat, and this is either charcoal or sand. 

 A case of brick-work, -with pulverized charcoal be- 

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

 other. A boiler ha\ing a surface of seventy feet 

 exposed to the air in a temperature of S'Z^ 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 sui'faces of this colour give out more heat 

 in a given time than any other. 



Solar light is essential to the ripening of all fruit ; 

 it ^^•ill not ripen in the dark, and the greater the 

 light's intensity and the longer its daily endiu'ance, the 



* For these rules I am chiefly indebted to ]\Ir. Tredgold's 

 valuable work on " Warming and Ventilation/' which will well 

 repay the gardener for the perusal.' 



