170 FIXED STRUCTURES FOR GROWING 



tubes, cisterns, or tanks of water. By arrangements of this kind, steam 

 can be made both to supply heat permanently and expeditiously. 

 Waste steam from mills and factories might often be turned to excel- 

 lent account by turning it into hot-water pipes. It forms a better cir- 

 culating force than most boilers, the motion of the water being well- 

 nigh instantaneous. The rate of the circulation and the degree of 

 heat generated can be regulated at will by stop-cocks. 



Hot water is the medium of heating plant-structures now generally 

 adopted, and it is without dispute far preferable to any of the pre- 

 ceding modes. Water is such an excellent carrier of heat, that a house 

 warmed by hot-water pipes is not hotter at one end than at the other, 

 which is almost always the case when smoke-flues are employed : none 

 of the heat which the water derives from the fuel is lost, as in the case 

 of flues, which when coated internally with soot convey a great part of 

 the heat out at the chimney-top ; no sulphureous or other disagree- 

 able effluvium is ever given out by hot-water pipes when they become 

 leaky, as is the case with flues when they are not air-tight ; and the 

 hot water in the pipes serves as a reservoir of heat when the fire goes 

 out ; but smoke-flues, when the fire goes out, are rapidly cooled from 

 within by the current of cold air which necessarily rushes through 

 them till it has reduced the temperature of their tops and sides to that 

 of the open air. Whether heating by hot-water is more economical 

 than heating by smoke-flues, will depend chiefly on the kind of appa- 

 ratus employed ; but in general we should say that it is not attended 

 with any advantages of this kind. Mr. Rogers is of opinion that with 

 a well-constructed. and well-managed apparatus, the saving of fuel may 

 amount to twenty-five per cent, over well-constructed and well- 

 managed flues ; but he allows that in a large proportion of the hot- 

 water apparatus now in use the consumption of fuel greatly exceeds 

 that of common furnaces. The cause of the circulation of water in 

 pipes is the same as that which produces the ascent of the air in flues 

 viz., difference of specific gravity produced by heat. In water, the 

 particles at the bottom of the boiler being heated become lighter and 

 rise to the surface, while their place is taken by cold particles from the 

 water in the boiler itself, or in the pipes that communicate with it, 

 which are heated in their turn, and ascend to the surface of the water 

 in the boiler and the surface of that in the upper pipe. In like 

 manner, the air heated by the consumption of the fuel in the furnace 

 becomes lighter, and ascends along the flue, while its place among the 

 fuel is supplied by cool air, which enters through the grating beneath 

 it to supply combustion. Neither air nor water will move along readily 

 in very small flues or pipes : for smoke-flues seven inches by ten 

 inches are the smallest dimensions, and hot water does not circulate so 

 rapidly in pipes under two inches in diameter as to give out heat equally 

 throughout their whole length. 



The modes of heating by hot water are very numerous, and it would 

 occupy too much room in this work to enter into a detailed descrip- 

 tion of them, which, however, is the less necessary as the best modes 

 are sufficiently known for all ordinary purposes by most ironmongers ; 



