THE FORCING GARDEN. 



liGUses, so as to consume the least possible quantity, is a de- 

 sideratum. " Heat is the same material, in whatever manner 

 it may be produced, and a given quantity of fuel will produce 

 no more heat when burning under a boiler, than when burn- 

 ing in a common furnace." 



FLUES. 



Various opinions have been entertained respecting the proper 

 size and situations of flues, and the materials of which they 

 should be constructed. The most primitive mode of their con- 

 struction appears to have been under the surface of the borders, 

 like drains, or in the solid walls of the house, and of large (hmen- 

 sions. Experience, however, soon proved the error, and we 

 have long found them built upon more correct principles. 

 Large, broad, and deep flues are used by the Dutch, and have 

 been recommended by a wTiter in the Caledonian Horticultural 

 Memoirs. Deep and narrow flues are used in Russia, and are 

 often met with in this country. Can-flues have been used for 

 a long period, but as they are rapidly heated and soon cooled, 

 they are only adapted for moderate fires; but, judiciously 

 chosen, they may frequently be more suitable and profitable 

 than common flues, as for example, where there are only 

 slight fires wanted occasion^illy, as in the case of a vinery with 

 late grapes, only requiring a slight fire to dry up moisture, or 

 repel a slight degree of frost, or where there is a regular sys- 

 tem of watching the fires ; in which case, but not otherwise, 

 the temperature can be sufficiently regulated. 



Cast-iron flues have been recommended on account of their 

 durability, but unless they were bedded in sand or masonry, 

 they are liable, in an extreme degree, to the same objections 

 as can-flues. Sir George M'Kenzie, the inventor of curvi- 

 linear hot-houses, has recommended what he terms an em- 

 brasure flue, upon the principle of its exposing a greater sur- 

 face of heated material in proportion to its length. It is 

 evidently a very unsightly flue, and possesses no merit to in- 

 duce our recommending it. Mr. Gowen"] in the Horticultural 

 Transactions, recommends a flue formed of bricks, which is 

 hollowed out in the middle, and of the usual thickness at the 



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