greater the production of soot, the more frequent the necessity of cleansing, and the smaller the flue in that case, the more troublesome will it be to keep it in order. In any case, however, periodical cleansing must be provided for, and for the flue of average capacity, iron soot doors answer best, or common flagstones may be employed. These should be inserted at the end of every straight line of flue; consequently, wherever the flue turns will be the place for a soot door or something equivalent thereto.
The furnace should be of brick, with double iron doors, and a damper above in the first part of the flue, and a valve in the door of the ashpit for regulating the draught. In determining the dimensions it is well to remember that a comparatively large fire burning slowly is to be preferred to a small fire with a brisk draught. But here, again, the nature of the fuel to be burnt must also be considered, for if it is of a kind that produces little smoke, the opening in front may be dispensed with. It is well, however, to provide for any kind of fuel, and especially for the consumption of the waste fuel of the household, for the cinders the servants “get rid” of will, in many places, sufrice for the preservation of a good collection of plants.
The flue system is now rarely adopted, having been in a great measure superseded by the hot water system, which will next be described. Plenty of good plant growing has been accomplished by means of flues, but they occupy much space, and are liable to crack and emit sulphureous fumes, to the sudden destruction of the plants they are intended to preserve.
The Hot-water System is so generally adopted that there are as many plans of apparatus provided for it as there are days in the year, and, as a matter of course, everybody’s boiler is the best. To a beginner in hothouse practice the variety of boilers must be extremely perplexing, but it will soon be found that they differ but little in essential particulars. In every case there is a furnace beneath a boiler or in the centre of it, and from the boiler proceed iron pipes, laid horizontally around and about the house. The heated water passes out of the top of the boiler into what is called the “flow” pipe, and having traversed the length of the house comes back to the bottom of the boiler by what is called the “return” pipe, and this motion of the water is described as the “circulation.” It is analogous
