AND CONSERTATORT. 15 



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, how- 

 ever, 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 equi- 

 valent 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 deter- 

 mining the dimensions it is well to remember that a compara- 

 tively 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 dis- 

 pensed 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, sufiice for the preservation of a good collec- 

 tion 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 measure superseded by the hot water system, which will next 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 accom- 

 plished 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 difler 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 



