446 



PITS AND FRAMES. 



on each side : the covers are of slate, 

 cemented so as to prevent the vapour 

 from rising up through the soil, and 

 raised 3 inches from the top of the tank, 

 so that the vapour of the hot water 

 comes in contact with the whole of the 

 under surface of the bed; and the bottom 

 heat from one end of the bed to the 

 other is nearly equal ; whereas, when the 

 covers are close down on the tanks, the 

 heat is very unequal. Into the vapour- 

 chambers four pipes were introduced for 

 the purpose of admitting vapour when 

 required in the pits. The covers of these 

 pipes are a piece of 1-inch thick wood, 

 made to project about half an inch over 

 the pipe all round : two holes are bored 

 through the wood, even with the inside of 

 the pipe, and opposite one another ; then 

 a piece of strong wire, a foot long, 

 is doubled, and an end pushed through 

 each hole, until the double of it forms 

 a handle, and the two legs below a 

 spring which presses against the sides of 

 the pipe, and keeps the lid at any height 

 to which it may be raised, and thus 

 prevents the hot vapour from ascending 

 directly to the foliage of the plants and 

 scorching them. 



" The ventilation of the back pit is the 

 only other thing to which I will direct 

 your attention. The back wall is hollow, 

 1 foot 8 inches deep, with the bricks 

 thrown across it to keep the wall strong. 

 The ventilators for the admission of air 

 on the outside are placed on the bottom 

 of the hollow wall ; and where the' air is 

 to enter the pit, the holes are at the top 

 of the hollow. Now, the cold air, when 

 admitted below, is obliged to travel to the 

 right and left, as shown by the arrows in 

 the wall, and at the same time rises a little 

 before it can enter the pit ; and in conse- 

 quence of this hollow wall being con- 

 nected with the hot-air chamber, it is 

 always full of warm air, so that the fresh 

 cold air gets the chill taken off it before 

 entering the pit." 



References to the letters marked on the 

 plan : aaaa tanks, b stoke-hole, c ash-pit, 

 d hot-air chamber, e cold-air drain. 



Dalkeith propagating -pit. — The an- 

 nexed section, fig. 621, and ground-plan, 

 fig. 622, exhibit this pit. It is connected 

 with a bulb-pit at a, ground-plan, which 

 shows the flow and return hot-water pipe 

 taking the water to the tanks b b from the 



boiler, which is placed in the division 

 between both pits, as seen in the follow- 



ing fig. 623, and at c in fig. 622, which 

 represents the flow-pipe from the same 

 boiler, the return-pipe being under it, as 



Fig. 622. 



seen in the section, both being placed in 

 a space separating the tank from the front 

 wall. The intention of the tanks is to 

 supply bottom heat to a bed of sand in 

 which cuttings are planted, or pots set or 

 plunged, when bottom heat is required. 

 The other pipes extend the whole length 

 of the pit, for producing atmospheric heat. 

 The tank extends about three-fourths of 

 the whole length, leaving the remainder 

 at e without bottom heat, being used for 

 hardening off newly-potted plants, &c. 

 Under tbfcs space, mould, sand, and pots 

 are kept for use. The tanks are of brick 

 and cement, covered with Welsh slates, 

 and having a frame of wood 10 inches 

 deep all round to keep in the sand or 

 plunging material. A shelf, /, is placed 

 along the front, which, being somewhat 

 shaded, is used to set newly-potted-oft 

 plants upon ; while another is suspended 

 from the roof g, and runs along the back 

 for those pretty well established in the 

 pots. These pits are sunk, as will be seen 

 by the ground-lines h h. They are 6 feet 

 wide within, and seven feet high at the 

 back, and are entered at the end at i. 



