SECTION IV. 



HOT-WATER BOILERS AND PIPES. 



1. Size of Boilers, and surface necessary to be exposed to the 

 fire. In adapting the boiler of a hot-water apparatus, it is not 

 necessary, as in the case of steam boilers, to have its capacity 

 exactly in proportion to the quantity of pipe that is attached to 

 it. On the contrary, it is sometimes desirable to invert this 

 order, and to attach a boiler of small capacity to a considerable 

 length of pipe. We do not mean, however, in recommending a 

 boiler of small capacity, to propose, also, that it should be of 

 small superficies ; for the efficiency of a boiler very much depends 

 upon the quantity of surface exposed to the fire. The larger 

 the surface exposed to the action of the calorific influence, the 

 greater will be the economy of fuel, and, therefore, the greater 

 will be the effect of the apparatus. 



In proposing the adoption of boilers of small capacity, how- 

 ever, it is necessary to accompany the recommendation with \ 

 caution against running into extremes, for this error has been 

 the cause of the inefficiency of apparatus in many instances. 

 In some boilers, we have seen the space allowed for the water 

 so very small that the boiler was thereby rendered completely 

 useless. 



Too small a quantity of water, and too large a surface exposed 

 to the fire, give rise to various evils, among which are the depo- 

 sition of neutral salts and alkaline earths by the water which 

 evaporates, contracting the water-way, and impeding circulation ; 

 and also preventing the full action of the fire on the exposed 

 surface of the boiler. 



But perhaps the greatest evil arising from this state of things, 



.is from the repulsion of heat by the metal of the boiler. The 



quantity of water it contains being so small, and the heat of 



the fire very intense upon it, a repulsion is caused between 



