DETACHED GREENHOUSES, ETC. 179 



the gas tar eats right into the grain of the metal, often 

 half through it, so that all surface applications are use- 

 less. Better let all painting of the pipes alone, as a 

 rather better radiation of heat is got if left unpainted. 



HEATING BY FLUES. 



When personal attention can be given to the fires, by 

 heating greenhouses with flues a great saving in cost can 

 be made ; in fact, nearly half the cost of construction ; 

 for we find that the hot-water heating apparatus usually 

 is half the cost of building greenhouses, while, if heated 

 by flues, the cost would not be more than ten per cent. 

 of the whole. A new method of constructing flues (or 

 rather a revived method, for it originated in 18^2,) has 

 been in use for the past few years, which has such mani- 

 fest advantages that many now use it who would no 

 doubt otherwise have used hot-water heating. Its pe- 

 culiarity consists in running the flue back to the furnace 

 from which it starts and into the chimney, which is built 

 on the top of the furnace. As soon as the fire is lighted 

 in the furnace, the brick-work forming the arch gets 

 heated, and at once starts an upward draft, driving out 

 the cold air from the chimney, which puts the smoke 

 flue into immediate action and maintains it ; hence there 

 is never any trouble about the draft, as in ordinary flues 

 having the chimney at the most distant point from the 

 furnace. It will be understood that the chimney into 

 which the flue is returned is placed on the top of 

 the arch of the furnace, and not in it, as some might 

 suppose. 



By this plan we not only get rid of the violent heat 

 given out by the furnace, but at the same time it insures 

 a complete draft, so that the heated air from the furnace 

 is so rapidly carried through the entire length of the flue, 

 that it is nearly as hot when it enters the chimney as 



