230 HORTICULTURE [HEATING. arch is turned leaving a space the depth of the top flue doors I, to serve as an upper flue, while the space below forms a lower flue. The grate bars are inside the cylinder towards the lower part, the space above them forming the furnace, and that below them the FIG. 39. Stevens s Trentham Boiler. ash-pit. The heat thus passes through the centre of the cylinder, then returns by the upper flue over its ton, and is conducted to the chimney by the lower flue, which arrangement is found to work better than when the heated air is made to pass through the lower flue first. Tubular Tubular Boilers. While the action of tubular boilers is rapid, and boilers, they are undoubtedly very powerful, they are said to be prodigal in their consumption of fuel, and liable to crack. In many cases, how ever, they have done good work for many years, and they are conse quently employed to a considerable extent. The original tubular boilers were horizontal, but the upright form has nearly superseded this, and the Upright Oval Tubular of Mr Gray, and the Duplex Upright Tubular of Messrs Weeks & Co., both of Chelsea, the latter marked by improvements introduced specially to meet the foregoing objections, are the best forms at present in use. The Duplex (fig. 40) is made in two equal parts, each being capable of FIQ. 40. Weeks s Duplex Tubular Boiler. being worked alone. Each section consists of a semicircle of up right tubes forming the boiler proper, fitted with the diaphragm a, by which more perfect combustion of the fuel is secured, a series of horizontal pipes forming the furnace/, a flow pipe b and a return pipe c, and an outlet d for removing sedimentary deposits from the interior. Ladds s Boiler (fig. 41) is a horizontal tubular, which is found to be extremely powerful as well as economical. It is a rectangular box 6 feet long, made of 2-inch iron pipes, fixed into hollow water spaces which form the ends ; these pipes act as fire bars, and form the sides of the furnace. Above the fire there are three series of horizontal pipes, each covered by a layer of tiles so placed as to convert the two intervening spaces into flues, along which the flames and smoke travel for 18 feet, the smoke escaping at the far end by an opening in the upper layer of tiles. Each tier of pipes FIG. 41. Ladds s Boiler. in its turn therefore gets its share of heat from the burning fuel, and the consequence is that the apparatus is very quick in its action. The tubes are fitted in with Portland cement and hempen cord packing tar ropes being found to destroy the cement. These boilers each heat 3000 feet or more of 4-inch piping. On the top of the upper layer of tiles are placed about 9 inches of ashes, then ordinary inch boards which rest on 4J-inch retaining walls, and on thes3 8 or 10 inches more of ashes, which very efficiently prevents any loss of heat. Stoves, <L-c. In the case of very small houses petroleum stoves or Sti lamps are sufficient to keep out all ordinary frosts, but they are attended with a disagreeable smell. A small conical or cylindrical boiler attached to a system of piping is by far the safest and best in such cases. The furnace heating may also be effected either with petroleum, or, better still, as requiring no attendance, with gas. The furnace should be accessible from the outside only, so that none of the products of combustion may enter the house. A small conservatory might be readily heated in this way from a furnace fixed in a recess of the back wall or in the basement of the house, and placed near one of the fire-places, so that the outlet may be con ducted into the chimney. A flow and return passing along under the side and front stage (avoiding doorways) might be kept heated by means of a small boiler of any form set over a circlet of gas jets. If on the level, the arrangement would be more simple still, since the boiler could be set in the house without brickwork, and the furnace constructed beneath it by piercing through the exterior wall, and fitting the opening with an ordinary furnace door. Hot-water pipes are best made of cast-iron. Tow or rope, and a Mi mixture of red and white lead, are generally used for packing or sh; caulking the joints, though some prefer vulcanized india-rubber an rings, which make good sound joints, and are very easily remov- of able ; for the joints near the fire iron cement must, however, be used. Flat pipes, and fluted or semi-circular pipes have sometimes been used, but the cylindrical form is much to be preferred. The number of pipes must be regulated by the extent to be heated, and the degree of temperature required ; it is often well to have three or even four flow pipes and only one return pipe. Pipes of 4-inch bore are almost universally employed, but 3-inch pipes may often be used in small houses. It is a mistake to stint the quantity of piping, since it is far more economical and better for the plants to have a larger surface heated moderately than a smaller surface heated to the highest possible degree. The pipes should, moreover, be placed near the front or lowest part of the house, and, to prevent loss of heat by conduction, should be sup ported clear of the ground, not less than 6 inches, upon cast-iron chairs. Mr Cannell of Swanley has adopted the plan of fixing two or Pi] three distinct lines of small piping close under the roof glass, soum as to prevent the air near the glass from getting cold. This roc contrivance is particularly useful in repelling damp during winter ; gla and it may also be adopted for wanning pits intended for the growth of half-hardy plants. Hot water may be beneficially applied to garden walls, not, He however, for the purpose of forcing the blossoms, but to assist in of
maturing late fruit and the young wood in unpropitious seasons.
