2oo THE POPULAR SCIENCE MONTHLY. 



It is clear from these considerations, that, in order to insure the 

 maximum effect from the fuel, the heating surface of the pipes should 

 be sufficiently large to warm all the air required without its being 

 necessary to raise the temperature of the water in the boiler to any 

 great extent, and the proportion between the boiler-surface and the 

 pipe-surface, that is to say, between the surface which absorbs heat, 

 and the surface which gives out heat, should be such as to render it 

 unnecessary for the fire to be forced, because, the lower the tempera- 

 ture at which the gases from the fire pass off up the chimney, the 

 greater will be the economy. 



In order to show the waste which results from forcing the boiler, 

 i. e., from passing the gases into the flue at a high as compared with a 

 low temperature, I will give an instance of one experiment. The pro- 

 portion of heating surface in the boiler to the heating surface of the 

 pipes is assumed by some manufacturers as 1 to 100, or, when great 

 heat is required, 1 to 40. An experiment made on 4,000 feet of pipe, 

 heating certain greenhouses by a wagon-shaped boiler with 40 square 

 feet of heating surface, showed that a certain temperature was kept up 

 for 8 hours with 8 bushels of coal ; but when, by the addition of an- 

 other boiler, the heating surface of the boiler was increased to 80 square 

 feet, the temperature could be maintained for the same period with 4 

 bushels of coal. The outer temperature was the same on the two days. 



On these grounds it is not so economical, so far as the consumption 

 of fuel is concerned, to use steam instead of water, either water heated 

 to a high temperature under pressure, or to heat air for warming pur- 

 poses, because the gases from the fire employed to produce the higher 

 degree of heat will pass off at a high temperature, and the heat they 

 contain be wasted. On the other hand, the capital outlay required, 

 where highly-heated pipes are used, is smaller than with hot-water 

 pipes, because a smaller heating surface, and therefore smaller pipes, 

 will suffice when the temperature is high ; and, moreover, a very small 

 pipe will convey steam to any required place, whereas with hot water, 

 at a relatively low temperature, much larger pipes are required. It 

 follows that where the price of fuel makes it necessary to reduce the 

 permanent annual expenditure, the original capital outlay must be in- 

 creased. There is a further consideration in regard to economy with 

 hot-water pipes, steam-heating, and all appliances for warming buildings 

 from a central fire, viz., that if the heat has to be conveyed for long 

 distances before its useful application comes into force, very much heat 

 is lost, and consequently fuel is wasted. On the other hand, against 

 the saving which would result from a more immediate application of 

 the heat to the place to be warmed, there is to be weighed the dimin- 

 ished expense of attendance consequent upon the use of one fire instead 

 of several fires, each with its attendance and supply of fuel. There 

 remains one source of economy to be applied to close grates used for 

 heating water, which has not yet been adopted. I mean the applica- 



