146 HEATING AS APPLIED IN HORTICULTURE. 



appearance. We have lately had speci- 

 mens of fire-clay flues of the pattern fig. 

 143, made in lengths of 6 feet each, and 

 tubular ones, 1 foot clear in diameter, of 

 the same length — thus lessening the num- 

 ber of joints, and forming in either case 

 the most elegant of all flues. The sides 

 are 2 inches thick, and are carried clear 

 of the ground by reposing on chairs of 

 the same material supported on brick 

 piers. 



Very elegant and useful flues can be 

 made of fire-clay tiles, 3 feet long, 1 foot 

 broad, and 2\ inches thick. These tiles 

 are to be set on edge, having bottoms 

 and covers of similar dimensions, and to 

 be half-checked, so that they may fit into 

 each other; and, to render them more 

 secure, they may be batted together with 

 iron clamps, placed inside, and flush with 

 the inner surface of the flue — the holes 

 for the bats being formed before the tiles 

 are burnt. 



Flues of the above descriptions, if made 

 from 2 to 3 inches thick, become, in fact, 

 a modification of our best brick flues, 

 having fewer joints, and having a more 

 elegant appearance. The advantage of 

 earthenware and fire-clay flues are, that 

 they can be erected at much less expense, 

 and are much sooner heated than any 

 other. On this latter account they are 

 valuable in greenhouses and pits for 

 half hardy plants, where heat is required 

 to be got quickly up to repel sudden 

 attacks of frost. An improvement on 

 these flues is, to leave the sides of the 

 tiles of the usual thickness, and to hollow 

 out their centres to half the thickness — 

 that is, to form each tile into a separate 

 panel, similar in principle to the bricks 

 used in Gowen's flue, noticed below ; and, 

 for greater elegance, a neat moulding 

 may be carried round the inner side of 

 each panel. They may also be portable, 

 and removed when not required. In 

 this case it will be best to pack the joints 

 with well-prepared fire-clay ; but if 

 intended to be permanent, they should 

 be jointed with cement or mastic. 



Broad flues — fig. 146 — have been re- 

 commended by Steven- 

 son in " Caledonian 

 Horticultural Society's 

 Memoirs." The only 

 advantage of them, 



them fit only for situations where power- 

 ful fires are kept up. 



Fig. 146. 



Fig. 147. 



Narrow and deep flues — 

 fig. 147 — were recommended 

 by the late Mr Oldacre, some 

 time gardener to the Emperor 

 of Russia. The advantage of 

 these, we confess, we could 

 never clearly see. 



-fig. 148. These 



Fig. 148. 



Flues 



are now seldom used, unless for carrying 

 off smoke from detached 

 flues running parallel to the 

 fronts of houses; and also, 

 in cases where hot water is 

 employed, it is better to 

 take the smoke, and conse- 

 quently the heat that passes 

 the boiler, along the back 

 wall, as exemplified in some 

 of the pine-stoves in the 

 gardens at Dalkeith. These 

 flues give out a certain por- 

 tion of heat, which it is 

 better to employ than to 

 lose by its escaping at the 

 chimney-top. By leaving square open- 

 ings over them, a considerable degree of 

 heat is thrown into the house from the 

 top and side, and the sheds behind are 

 kept both dry and warm by the heat that 

 escapes from the opposite sides of the flues. 



The embrasure flue — fig. 149 — is an in- 

 vention of Sir George Mackenzie's, and 



Fig. 149. 



Fig. 150. 



recommended by him as exposing a much 

 greater heated surface in proportion to 

 its length than the ordinary or straight 

 flue. The merits of this flue have been 

 said scarcely to counterbalance the extra 

 expense of erection ; we, 

 however, think differently, 

 and have seen them work 

 admirably, as any one ac- 

 quainted with the nature 

 of heat will readily see by 

 the diagram. 



Gowerfsflue — fig. 150 — 

 requires bricks and covers 

 to be made on purpose : 



however, is a slower draught, rendering they are of the usual thickness at the base, 



