176 



HEATING AS APPLIED IN HORTICULTURE. 



tion is attained by regulating the supply 

 of air to the furnace to the lowest extent 

 possible, so as merely to keep up the re- 

 quired heat in the boiler, and prevent the 

 fire from becoming extinguished. The 

 boiler is a modification of Rogers' conical 

 one, which, Mr Smith observes, is no 

 very new invention, having been em- 

 ployed by the Union Canal Company at 

 the suggestion of the late Sir John Robi- 

 son, for warming their passage-boats, 

 twenty years ago. Mr Smith's boiler is 

 fitted into a sheet-iron case, with a cast- 

 iron bottom and ash-pit door, which is 

 grooved to fit the frame closely for the 

 exclusion of air. The boiler a is sur- 

 rounded with sand, having a sand-joint 

 for the door at top g. No air is admitted 

 to the fuel except that which enters the 

 furnace through the register in the ash- 

 pit /, and on this the steadiness and 

 slowness of combustion depends. The 

 fuel is supplied by removing a part of 

 the top at k, and the smoke passes off 

 through the pipe h. The pipes are placed 

 as in the section fig. 212, b b, either ver- 



ig. 212. 



tically, as here shown, or horizontally, as 

 may be most convenient ; and Mr Smith 

 suggests that they should have a gradual 

 rise from the boiler to the highest point 

 to which they may be carried. An air- 

 cock d and expansion-cistern c are placed 

 at the highest point, the latter being con- 

 nected with the pipes by a small tube. 

 The furnace e is placed in the centre of 

 the apparatus ; a piece of sheet-iron I is 

 bolted to the case, at which point the 

 pipes are connected or disconnected with 

 the boiler by coupling screws m, while n 

 is a tap for drawing off the water, and / 

 is the ash-pit. According to the length 

 the pipes may be carried, coupling-screws 

 are attached, so that the whole heating 

 power can be shortened or lengthened at 

 pleasure, as well as taken to pieces in case 

 of a change of position being desirable. 

 Mr Smith recommends, when the appa- 

 ratus is likely to be portable, that the 



pipes be made of copper ; we see no reason 

 why 2-inch leaden ones would not do as 

 well, and they would be much cheaper. The 

 boiler is to be placed outside the pit or 

 frame, and protected by a wooden covering. 



The following diagrams of boilers we 

 prefix to this article. The pipes, &c, 

 being attached to them in the usual man- 

 ner, we do not deem it necessary to spe- 

 cify them under the denomination of any 

 particular mode of heating, as they may 

 be applied to almost any of those already 

 described. 



Neeves boiler^ of which the annexed fig. 

 213, presents a transverse and a longitu- 



Fig. 213, 



dinal section. Mr Neeve was an early 

 improver on hot-water boilers ; and being 

 in his youth the principal assistant of the 

 late Mr Tredgold, he completely under- 

 stood the subject both in theory and prac- 

 tice. On this subject, after acquiescing 

 in the correctness of the rules laid down 

 regarding the surface of pipe, &c, he says, 

 " Still I think that the calculation for the 

 size of the boiler is not sufficiently clear ; 

 for a furnace may be so constructed, that 

 although a given quantity of fuel may be 

 consumed in a given time, yet a great 

 portion of the heat from that fuel may 

 escape through the flue, without being of 

 service to the boiler." This is substan- 

 tially true ; and no boiler has yet been 

 invented that will take up all the heat 

 from the fire burning under it, as water 

 is capable of extracting only a certain 

 amount of caloric, and beyond that point 

 it cannot go. Hence, under all circum- 

 stances, a certain amount of heat must 

 be lost, unless it can be turned to account 

 by passing through a flue or otherwise, 

 after passing the boiler, or unless the 

 quantity of fuel can be so graduated as 

 to heat the water in the boiler to the de- 

 sired point and no more — a matter, we 

 presume, of no small difficulty. 



