HOTHOUSE FURNACES. 



251 



§ 8. — HOTHOUSE FURNACES. 



The hothouse furnace described by 

 Nicol about the beginning of the present 

 century, is still very generally in use, and 

 may be understood by the following de- 

 scription of it in his own words : " It is 

 simply an oven, capable of containing less 

 or more fuel, according to the kind of 

 hothouse to which it may be attached, 

 and the kind of fuel to be used." His 

 medium size is of the following dimen- 

 sions : — " The oven is 30 inches long and 

 20 inches wide ; the grate 18 inches long 

 and 10 inches broad; the furnace-door 

 10 inches square, with a circular valve in 

 the centre of it 3 inches in diameter ; the 

 ash-pit door is of the same construction 

 and width, but 15 inches deep. These 

 valves turn with a handle, and are cap- 

 able of admitting any quantity of air to 

 the extent of half their diameters, which 

 is deemed sufficient. The sole of the oven 

 is placed 12 inches below the level of the 

 flue, and is paved with firebrick. The 

 walls are also formed of firebrick to the 

 height of 12 or 15 inches, and the arch 

 is turned with the same material. Fire- 

 clay is used instead of lime." 



Little improvement has taken place on 

 this furnace up to the present time, if we 

 except the introduction of larger bricks 

 in its construction, thereby lessening the 

 number of joints, and the lengthening out 

 the floor by introducing dead-plates be- 

 tween the fire-bars and furnace door. The 

 first improvement made on Nicol's fur- 

 nace was by the late Mr Loudon in 1 803, 

 who added a double door, upon Count 

 Rumford's principle. Hay, Steuart, At- 

 kinson, and others, about the same time 

 turned their attention to the subject ; but 

 we observe little alteration of consequence 

 made by any of them, excepting by the 

 latter, who introduced brass registers in 

 ash-pit doors, instead of the iron ones 

 used by Nicol, as being less liable to cor- 

 rosion, and of course much easier opened 

 and shut. He also added the dumb or 

 dead plate, which is either a plate of 

 thick cast-iron, or a strong fire-clay tile, 

 placed between the opening of the door 

 and the front end of the bars or grate, 

 laid in a slanting direction, having an in- 

 clination of from 3 to 4 inches from the 

 door towards the grating, and from 1 foot 

 to 18 inches in length, according to the 



size of the furnace. A similar dumb- 

 plate was placed between the inner end of 

 the grating and the throat of the furnace, 

 laid slanting upwards in the direction of 

 the floor of the flue. Upon the front 

 dead-plate the fresh supplies of fuel are 

 laid, and become pretty well carbonised, 

 being ignited by the fire on the grate. 

 While it burns slowly there, the smoke is 

 given out, and, having to pass over the 

 fire on the grate, becomes to a certain 

 extent consumed. 



It may here be remarked that this was 

 the first attempt to consume smoke, at 

 least in garden structures ; and fires ma- 

 naged as directed by him, and detailed 

 in the latter end of this article, are 

 found to answer the purpose very satis- 

 factorily. The great advantage of double 

 doors and ash-pit registers — the latter 

 first suggested by Dr Black, and after- 

 wards put in practice by Count Rumford 

 — is the command they give the fireman 

 over the state of the fire. By shutting 

 them closely up, the process of combus- 

 tion is lessened from the want of air, and 

 the fire may be kept in a state of suspen- 

 sion, as it were, for many hours ; while 

 on opening the register either in the door 

 or the ash-pit, air is admitted, and combus- 

 tion goes on. Indeed it is impossible to 

 regulate the temperature of any house 

 without these necessary appendages and 

 their proper application. As regards the 

 size of furnaces, we may remark that, 

 where the best Newcastle coal is used, a 

 furnace will be amply sufficient of half 

 the size of that required where inferior or 

 Scottish coal is alone to be got. 



To understand the defects of the fur- 

 naces in common use, we should consider 

 that the greatest part of the floor— often 

 the whole of it — is taken up with the 

 grate, which is also, in many cases, too 

 wide in the bars. They frequently have 

 two ill-fitted doors, one to supply the fuel, 

 and the other to remove the ashes. This 

 unnecessary extent of grate and doors 

 admits too much air, by which the fire 

 is not only kept below the temperature 

 sufficient to consume the smoke, but also, 

 as soon as the door is opened, a vast 

 quantity of cold air sweeps over the fire 

 and through the flues, carrying along 

 with it three-fourths of the heat in them 

 out at the chimney-top. Then the cold 

 damp coal is thrown into the centre of 



