324 



SCIENCE OF GARDENING. 



Part II. 



271 



1649. The iron doors admit of several varieties ; but it does not appear that there is any- 

 great difference in the effect produced by the different plans of Nicol, Hay, Stewart, and 

 others. A double door has the advantage of durability, of preserving heat, and of not so 

 readily admitting cool air to pass over the fire ; which air, of course, must be less heated, 

 and consequently less capable of heating the flue than such as, entering from below, passes 

 through it. The use of the ash-pit door is to act as a regulator to the current of air, or as 

 a damper or suffocator. 



1650. Vacuities have been formed around furnaces, and by communications between these 

 and the open air, and an air -flue in the house, a stream of heated air has been introduced : 

 but this air is so little at the command of the gardener ; is so dried up or burnt, as the 

 phrase is, that is, mixed with offensive gases from decomposed water, burned oil, iron, 

 sulphur, or very fine dust ; and so liable to be mixed with smoke, that such plans are now 

 generally laid aside. Vacuities, however, are frequently formed round furnaces, and 

 along the first four or six f 2et of the flue, in order to temperate the heat in that part ; but 

 such vacuities rarely have any communication with the air of the house. Where a house 

 of considerable length and volume is to be heated, it is generally deemed better to increase 

 the number of furnaces than to increase their size, or have recourse to air-flues ; for when 

 the latter practice is resorted to, they are necessarily projected so far into the shed, or 

 otherwise kept back from the house, that a great part of the heat is lost in the mass of 

 brick-work which surrounds them. Small furnaces, on the contrary, may be built in great 

 part under the walls or floor of the house. In countries where turf, wood, or inferior 

 coal, is used for fuel, the chamber of the furnace must be large ; on the contrary, where 

 the best coal, cinders, charcoal, or coke (the three last, the best of all fuel for hot-houses, 

 as having no smoke), is used, they may be made smaller in proportion to the different de- 

 grees of intensity of the heat produced by these different materials* In fixing on the 

 situation of furnaces, care must be taken that they are always from one to two feet under 

 the level of the flue, in order to favor the circulation of the hot air and smoke, by allow- 

 ing it to ascend. 



1651. A small lime-kiln {fig. 271. a) is 

 in some places constructed or fixed over 

 hot-house furnaces for burning lime ; and 

 when the heat, which passes through the 

 limestone, is made to enter the flues (<j), 

 it is evident a real benefit must result from 

 the practice, as the heat applied to the 

 burning of the lime in the common way 

 escapes in the atmosphere. The grate 

 or fuel bars (rf) are contrived to draw 

 out, by means of a grooved frame (c), 

 so that when the lime is burned, it then 

 drops into the ash-pit (6). 



1652. As to the size of hot-house fire- 

 2)laces, the door of the furnace may be from 

 ten inches to one foot square ; the fuel- 

 chamber from two to four feet long, from 

 eighteen inches to two feet wide, and of 

 the same dimensions as to height. Every 

 thing depends on the kind of fuel to 

 be used. For Newcastle coal, a chamber 

 of two feet long, eighteen inches broad, 



and eighteen inches high, will answer as well as one of double the size, where smoky 

 Welsh or Lancashire coal is to be used. Various contrivances, as hoppers, horizontal 

 wheels, &c. have been invented for supplying fuel to furnace-fires without manual labor, 

 and especially during night ; but from the nature of combustion, and the common mate- 

 rials used in this country to supply it, no effectual substitute has yet been discovered. If 

 wood or charcoal, or even cinders or coke were used, there would be a greater chance of 

 such inventions succeeding, but we do not think ourselves warranted in detailing any of 



them. ", . . . ... 



1653. The modes of constructing flues are various. The original practice was to build 

 them on the naked earth, like drains or conduits ; or in the solid walls of the backs and 

 fronts of the pits, like the flues of dwelling-houses. The first improvement seems to have 

 been that of detaching them from the soil by building them on flag-stones, or tiles sup- 

 ported by bricks ; and the next was, probably, that of detaching them from every descrip- 

 tion of wall, and building their sides as thin as possible. A subsequent amelioration 

 consisted in not plastering them within, but in making their joints perfect by lime-putty, 

 by which means the bricks were left to exert their full influence in giving out the heat ot 

 the smoke to the house. 



