POLMAISE METHOD OF KEATING HOTHOUSES. 



61 



is the case, they are built of fire-bricks, as are also the flues ; and 

 wherever the walls are likely to be much heated, they are Stour- 

 bridge fire-bricks, set in the same clay, being-, in my opinion, 

 more durable than Welsh lumps ; it will be well to parge the 

 outside of the walls of the stove. The stove is 3 feet high, 

 which allows 3 inches for paving of ash-pit + 1 foot for depth of 

 ash-pit + 3 inches for depth of bars + 1 foot 6 inches for depth 

 of furnace from bars to plating = 3 feet. The iron top is 

 formed of three plates, with a view to allow of expansion ; two 

 of these plates have extending rabbets, so that when laid in place 



they have this appearance. , r^rpi j » , 



They are 1 foot 6 inches one way by 3 feet 6 inches the other, 

 so that when laid in their place, and the space for expansion be- 

 tween each allowed, they form a surface of 4 feet 7 inches by 

 3 feet 6 inches. This, by calculation, will be found to give them 

 a 4-inch bearing on the four outside walls of stove. Along the 

 wall of stove next the hot-house, a course of thin brick is laid, 

 not close to the edge of plating, but half an inch from it. The 

 two end walls are carried up three courses higher in 4i-inch 

 work, and so also the outer wall ; and between all these and the 

 edge of plating there is a half-inch space ; the purpose of this 

 groove is to fill it with sand, so that the plates can expand and 

 squeeze up the sand, while, when they contract, this will follow 

 back and keep the joint air-tight. I am assured, however, by 

 practical men of great experience, that it will be found quite un- 

 necessary to have the plates cast in three pieces ; that it would 

 suffice if cast in one piece, provided it were cast with a loop 

 round the edge, which should fall into a groove of sand, and that 

 the plate would then expand in the loops : this will greatly lessen 

 the danger of exhalation. The situation of the damper, as shown 

 in section, is bad ; it should be placed exactly at the junction of 

 the flue with the chimney; and it will be found to economize fuel, 

 by preventing the loss of heat, if between the brickwork form- 

 ing the end of chamber and the stove some non-conducting 

 material, such as hair-felt, be placed, and also if double doors be 

 used for the furnace. I find the only loss of heat that takes place 

 in the apparatus at Nutfield is from the furnace-doors and the 

 bricks around them, and this might be prevented by the above 

 plan. The doors employed are Sylvester's patent, which, for all 

 purposes where the regulation of draught is required, seem to be 

 the best that can be imagined ; there are no hinges to rust, or 

 machinery to get out of order, or screws to untwist ; they simply 

 hang on a frame, in which they slide, the edges of the door and 

 frame being ground to fit ; and another advantage which they 

 seem to me to possess is, that if any explosion should take place 



