On the Construction of Flues of Hot-Houses. 



215 



nary construction ; and even in situations where they are 

 easily got, gardeners almost universally complain of the 

 trouble they occasion, and of their rapidly wasting. There 

 can be no doubt that the best form for a flue is that of a 

 cylinder, which is the form of what have been denominated, 

 in the " Memoirs of the Caledonian Horticultural Society,"* 

 Can flues ; but it is obvious that while the cost of such flues 

 is considerable, they are more liable to damage ; and they are 

 more expensive in repair than any other. It is a pity that 

 these objections are so strong ; because the peculiar advantage 

 of cylindrical flues is, that, while there is radiation from the 

 whole surface, the air is rapidly heated by its being in contact 

 all round. 



The application of cast iron to the construction of flues has 

 been often thought of, but, in my opinion, too hastily rejected. 

 To have this material in the form of tubes, may be objected 

 to on the score of expense, as well as unwieldiness ; and it 

 may be urged against its use, under any form, that it is apt to 

 crack on the application of cold water, which cannot be 

 avoided when water is given to the plants in a house. The 

 advantages which cast iron offer, are, however, so great, that 

 I have kept it long in my view ; and at length I feel myself 

 warranted in recommending for trial, a form of flue, con- 

 structed chiefly of iron, which seems to embrace every thing 

 that is desirable. 



The figure represents a section of the flue in its complete 

 state : A. B. is the bottom, made of cast iron, three-eighths 

 of an inch thick, having two ledges to support the other pieces 

 of cast iron of the same thickness, A. D. and B. D. When 



* Vol. I. page 65, and page 353. 

 VOL. V. F f 



