334 Memoirs of the Caledonian Horticultural Society. 



ends of brick built out of the walls of the chamber in an irregular manner, 

 so as to touch the outer wall, for the purpose of strengthening the inner 

 one; but these must not be so numerous as to prevent the heat from 

 rising and diffusing itself freely through the pits. 



" c c, Brick pillars, 9 in. square, supporting the cover of the steam- 

 chamber, &c. 



" d d, Pieces of rough flags, 6 or 7 in. broad, and 3 thick, linteling 

 over the open space between the brick pillars, and supporting the inner 

 wall of the steam-flue e e. This wall is 3 in. thick, built of stock bricks, 

 and closely jointed with Roman cement. The depth of the plant pit is 

 20 in. 



"ff, A course of bricks, 9 in. broad, for the seat of the steam-pipes. 

 On each side of this is a gutter 3 in. broad, and the same in depth ; the 

 floor of the steam-chamber has a rise of 3 in. on both sides, from the edge 

 of the gutters to the outer walls ; and is paved with hard common bricks 

 laid in lime. The upper bed of the lintel (d d) is 2 ft. 10 in. in height, 

 above the floor of the pit at the wall. 



" m n o, Cast-iron steam pipes, of 3 in. bore (in some cases they are 

 3 J in.), on the opposite sides of which, a line of half-inch holes (g g) are 

 bored at 2 ft. distance from each other, in quincunx order : there is thus 

 one hole for every foot of pipe in length. 



" h h h, Cisterns cut out of solid stone, 6 in. square, and 6 deep, having 

 grooves a quarter of an inch deep on the top of the opposite edges at the 

 gutters. As the ground on which the pits are built falls from east to west, 

 the condensed steam in the east division of pipes returns into the boiler ; 

 but, as on the west it cannot do so, pieces of* pipe three fourths of an inch 

 bore, and 4 in. in length, are cast on the under side of the steam-pipe at 

 h h h, in the west division. The condensed steam passes through these 

 pipes into the cisterns, and flows over into the gutter, as does also the con- 

 densed steam from the chamber, and is carried off by the small drains i i. 



" k 7c, Cast-iron rollers in frames, on which the pipes rest, the under 

 part of the pipes being 2|in. above the brick seat. 



" / /, in jig. 55., and in fig. 57., are slide valves or cocks, by which the 

 steam is admitted at pleasure into the pipes of the 

 melon- pit. The draw-rod passes through an oblong 

 opening in the cover m, which is of polished Ar- 

 broath pavement, and the opening is covered over 

 with an oblong piece of brass about five eighths of 

 an inch thick, secured to the stones by bats and 

 screws. This piece of brass has also an oblong 

 opening, through which the rod of the valve passes 

 to the outside of the plant-pit, and is of such length 

 as to allow for the elongation of the iron pipes when 

 heating, and their contraction in becoming cold. 

 On the surface of this piece of brass is placed an- 

 other, furnished with a stuffing-box, through which 

 the rod passes, and keeps it in its place. Both are fitted close to each other, 

 and kept down by a leaden weight ; and thus the escape of steam from the 

 chamber below into the atmosphere of the pit is prevented. After this 

 simple apparatus has been adjusted, the cross handle of the rod is fixed on 

 with a screwed nut. 



" n, A stuffing-box, made of two pieces of sandstone, batted together, 

 with a circular cast-iron cover bolted to the stones ; the box is stuffed with 

 lint and a little tallow, to prevent the heat and steam from passing from 

 the one pit into the other. The pipes being laid, small brick pillars (o o) 

 are built on each side, about 5 in. higher than the upper side of the steam 

 pipe. These pillars support pieces of rough flags (p) in the section, cross- 



piiik ifflii , 



