HOTHOUSE FURNACES. 



261 



Magazine," vol. xvi. p. 136 : " When the 

 fire is first lighted, it should be allowed 

 to burn brisk and clear, till the fuel in 

 the bottom is well ignited ; it may then 

 be filled up to the throat of the furnace, 

 when it will last through the night. In 

 filling, care, of course, must be taken 

 that the fuel is not so small and dusty 

 as to stop the draught. As fuel cannot 

 be consumed without air, if a furnace 

 be constructed of considerable depth," 

 (the form of Mr Rogers' boiler being 

 conical, it follows that his furnaces are 

 deeper than those under boilers in a 

 horizontal direction — still the philosophy 

 of combustion is pretty much the same 

 in both cases,) " and filled with fuel, and 

 air be admitted only at the bottom, that 

 fuel alone is consumed which lies imme- 

 diately on the bars, and first receives 

 the draught of air. The fuel above, 

 providing it transmits the air, becomes 

 red hot, or nearly so, but does not con- 

 sume, until that below it is destroyed. 

 In this manner, one of these conical 

 furnaces being lighted and filled with 

 fuel, that portion in the upper part of 

 the furnace which cannot burn, absorbs 

 the heat of the burning fuel below, and 

 radiates or transmits it to the water on 

 every side. So perfect is this absorption 

 of heat, that for several hours after the 

 furnace has been filled up with cinders, 

 though there may be a fierce fire below, 

 little or no heat escapes by the chimney, 

 the whole being taken up by the sur- 

 rounding water. The economy, there- 

 fore, of fuel in such an apparatus is very 

 great ; and it is also evident that excess 

 of draught must be guarded against, so 

 much only being allowed as will con- 

 sume the fuel steadily, which is easily 

 learned by experience. The necessity 

 also of keeping the aperture in the 

 front close, so that air enters the fur- 

 nace only through the ash-pit, is hence 

 evident." 



Besides the proper construction of fur- 

 naces, much of the success of their opera- 

 tion depends on the manner in which 

 they are attended to. This is a matter 

 sadly neglected, not only in gardens, but 

 in all large establishments, even where 

 regular engineers are employed in super- 

 intending them. Nor is it a subject 

 much treated on, in works of horticulture 

 at least. The first, and almost the only 



useful instructions we know of in a pub- 

 lished form, are given in a paper "On 

 the Management of Hothouse Furnaces," 

 by the late W. Atkinson, Esq., in the " Hor- 

 ticultural Society's Transactions," vol. v. 

 p. 467. They are to this effect : "When 

 the fire is first lighted, the ash-pit door 

 may be left open till the fuel be properly 

 kindled. The door should then be shut 

 close, leaving the brass register so far 

 open as to allow sufficient air to blow the 

 fire, but not more than is absolutely ne- 

 cessary to make it burn well — not vio- 

 lently, nor with a strong draught ; for if 

 more air be admitted than is required for 

 a moderate brisk fire, it occasions a great 

 waste of fuel without increasing the heat. 

 The fire-place door must at all times be 

 kept shut, and the sloping part of the 

 iron frame of the door must be kept clear 

 of coals, so as not to prevent the door 

 from latching. No air must be let in at 

 the door at any time, except when it can- 

 not be avoided, in feeding the fire. Any 

 cold air that may get in at the fire-place 

 door is apt to rush over the fire into the 

 flue without being heated, and that air 

 tends to cool the flue instead of heating 

 it. Therefore, all the air that is neces- 

 sary for blowing the fire must be ad- 

 mitted at the ash-pit register, in order 

 that it may get heated in passing through 

 the fire to the flue. 



" It is impossible to determine the 

 exact opening necessary to be left in the 

 ash-pit register to admit sufficient air, as 

 that greatly depends upon the goodness 

 and length of the flue, and the height of 

 the chimney. 



" When a flue is once properly heated, 

 the draught becomes stronger, and then 

 a smaller opening in the register is suffi- 

 cient to supply the fire with air. In this 

 state, about ^ an inch opening in the 

 register is generally sufficient, and it 

 should be shut quite close, if it will be 

 found that the fire will burn in that posi- 

 tion, as a considerable quantity of air will 

 get in through the joints of the ash-pit 

 door. The best fuel for hothouse fire- 

 places is cinders or braise. This is cheaper 

 than using coals only, and keeps up a 

 steadier fire with less smoke. At all 

 times when fresh fuel is added to the fire, 

 the hot fuel unconsumed must be pushed 

 with an iron rake towards the further 

 end of the bars, and fresh fuel applied 



