PITS HEATED BY HOT WATER, &c. 



451 



breadth, as are also the side walls to the 

 height of 6 or 7 inches. Down the middle 

 of each pit let a line of bricks set on edge 

 be placed, leaving the one nearest the ex- 

 treme ends out : this will give a flow and 

 return current ; the line of bricks form- 

 ing the outer edge of each tank being kept 

 3 inches clear of the side walls, to prevent 

 the loss of heat by absorption or other- 

 wise. Over the tanks thus formed, thick 

 slate or thin pavement is to be laid, and 

 closely jointed with cement, extending 

 from back to front of the pit. Apertures 

 at every 5 or 6 feet may be cut in them, 

 to which iron or earthenware tubes should 

 be attached, of 4 inches in diameter, and 

 furnished with stoppers, to be taken out 

 for the admission of moist heated air into 

 the atmosphere of the pit, and replaced 

 when that is not required. Similar pro- 

 vision should be made over the apertures 

 between the outer edges of the tanks and 

 the side walls, to allow the heated air in 

 them free access into the pit ; and as the 

 air from such sources is not over moist, 

 the openings may be left uncovered. The 

 back walls may be 3| feet high above the 

 ground-line ; that is, allowing 8 inches for 

 the depth of water and thickness of the 

 top covering, and 2 feet 10 inches from 

 the top of the covering to the glass. The 

 front wall above ground-line should be 2 

 feet 6 inches. Circumstances will always 

 direct this, as the height of pits must be 

 suited to the purpose for which they are 

 intended. The boiler will supply all, or 

 part, as maybe required; and this can be 

 regulated by stopcocks placed in the 

 pipes which connect the boiler with the 

 tanks ; and these again can be subdivided 

 by sluices, as in fig. 251. By this means 

 we would have 1200 square feet of sur- 

 face heated by one fire ; and for the pur- 

 pose of growing young plants in pots, 

 forcing French beans, strawberries, aspa- 

 ragus, potatoes, salads, &c, such pits 

 would be invaluable. The walls should 

 be 9 inches thick, for durability, and also 

 for retaining the heat, or for the exclusion 

 of cold ; and if they are built hollow, so 

 much the better. The rafters and wall- 

 plates should be of iron, and the sashes of 

 the best Baltic or sound yellow pine timber. 

 The glazing should be with crown glass, 

 in sizes 6 inches by 1 0. To use larger glass 

 in such structures is unnecessary. The 

 roof may be on the ridge-and-furrow prin- 



ciple, without much difference in the cost. 

 The range should extend from east to 

 west, so as to present the frontage to the 

 meridian, or nearly so. 



To heat the greatest possible space, at 

 the least possible expenditure of fuel and 

 cost of erection, we think this and the fol- 

 lowing the best of all methods. 



Fig. 632 represents a span-roofed pit 

 extending to the length of 100 feet from 



Fig. 632. 



north to south, and 12 feet in breadth 

 within the walls, of which the footpath 

 occupies 2 feet 6 inches. The boiler is 

 placed in the middle, at one side of the 

 pit, its top being level with the floor of 

 the passage, and placed under the side 

 tank. The stoke-hole is to be sunk by 

 the side of the pit, so that the fire can be 

 managed from without. One flow-pipe is 

 to rise perpendicularly from the top of the 

 boiler to the surface heating pipe, and 

 another from the end of the boiler passing 

 under the footpath and opposite tank, and 

 rising with a gentle bend to the flow-pipe. 

 These pipes branch out to the right hand 

 and to the left, and are carried to the two 

 extreme ends of the pit, where they are 

 bent down and made to return towards 

 the boiler in the hot-air tank, formed of 

 pavement for top and bottom. The bot- 

 tom is supported by cast-iron brackets 

 set in stone plinths by the side of the 

 footpath — these plinths rising perpendicu- 

 larly to the height of the beds, and serving 

 the purpose of supports, to which the long 

 narrow strips of Welsh slate are secured 

 which form the sides of the beds, to the 

 depth of 12 inches. To these, at every 

 25 feet, the arched supports of the ridge 

 are fixed. Bottom ventilation is obtained 

 by 4-inch openings in the side walls, 

 opening into a 9-inch area extending the 

 whole length of both sides of the pit. 

 This area is provided with a cast-iron 

 covering, the frame-work of which is fixed 

 to the top of the area wall, as well as to 

 the sides of the pit, having its upper part 



