PITS HEATED BY HOT WATER, &c. 



443 



heated from a boiler adjoining. The 

 spaces /, between the hot-water-pipe 

 flue and the back wall, are to be made 

 solid with earth and rubbish, so as to 

 form a good foundation to the connecting 

 openings or flues to be laid on top of 

 them. Those between the said flue and 

 the front wall, g, should be filled with 

 hard, dry, open materials. 



In fitting this pit for the reception of 

 plants, the space between the hot-water- 

 pipe, flue, and the front wall of the pit, as 

 well as the whole surface of the pit over 

 the flue, and the space between it and 

 the back wall, should be covered, as 

 shown in the section, with stones, brick- 

 bats, or coarse gravel, to the depth of not 

 less than 12 inches. Over this, if for 

 melons or cucumbers, is to be placed a 

 layer of turf, with the green side under- 

 most, and over it the necessary com- 

 post, h. If the pit is intended for pines 

 in pots, or other plants, then gravel or 

 coal ashes may be substituted. 



" By this arrangement it will be per- 

 ceived," says Mr Rogers, (in his commu- 

 nication on the subject to the " Gar- 

 deners' Magazine,") " three things are 

 attained — bottom heat, top heat, with an 

 atmosphere constantly moist, and finally, 

 a constant circulation of air. Unless I 

 am much mistaken, supposing the pit to 

 be 6 feet wide, and 3 feet high at back, and 

 1 foot 3 inches in front above the mould, 

 the whole atmosphere of such a pit would 

 pass through the flue once in every two 

 minutes when the apparatus was in full 

 work, thus producing a constant and 

 vigorous circulation. Farther, if it be 

 desired to change a portion of the air 

 continually, small apertures to the out- 

 ward air may be made in the front 

 descending flues: a small portion of 

 fresh air will then pour in, continually 

 mingling with the descending air, and 

 ascending heated into the pit, supplying 

 the place of that which will escape 

 through unputtied laps and various cre- 

 vices. The internal areas of the pilaster 

 flues should not be less than 6 inches 

 square, which they may be according to 

 the" proposed plan; and the cross flues 

 and apertures into the pit must have the 

 same area. If it be found that, with this 

 area or apertures, the heat produced by 

 the pipes is brought up too rapidly, not 

 having sufficient bottom heat, and over- 



heating the top, these apertures may be 

 diminished. If they be too small, an 

 inequality will arise between the tempe- 

 rature of the back and front of the pit, 

 caused by an excessive difference of the 

 ascending and descending air. The total 

 heat brought up will be the same ; for as 

 the heat increases, the velocity with which 

 the air will ascend will increase also ; but 

 if apertures of the size above recom- 

 mended be employed, there will not be 

 2° difference between the front and back 

 of the pit. In order the better to dis- 

 perse the ascending currents, it may be 

 well that the aperture, instead of opening 

 directly into the pit, should have a semi- 

 cylindrical draining-tile placed in front 

 of it, to throw its draught right and left ; 

 but this is an unnecessary refinement; 

 a pair of 4-inch pipes will be found suffi- 

 cient for cucumbers and melons, or pines, 

 in a 6-foot pit." Regarding the tempe- 

 rature thus secured by two pipes, Mr 

 Rogers candidly observes that it may be 

 insufficient " for early forcing," and con- 

 sequently for hot pits during the winter. 

 He very properly suggests the employ- 

 ment of four instead of two pipes ; but 

 we apprehend that if a nozzle-pipe were 

 attached to the boiler, and if the flue in 

 which the pipes are placed was rendered 

 water-tight, so as to constitute a tank, 

 temperature enough would be attained 

 without going to the expense of the extra 

 set of pipes; and such an arrangement 

 would give out a far more genial and 

 humid heat. 



In this pit, as well as in most others 

 heated by hot water, it quite clearly 

 appears that much of the heat of the 

 furnace must be lost by escaping at the 

 chimney-top. We see no reason why this 

 heat, after passing the boiler, should not 

 be turned to advantage, by being made 

 to pass along in a smoke-flue, under 

 the heated air-flue, in the chamber / 

 To effect a complete command of heat 

 in this otherwise excellently contrived 

 pit, we think it would be requisite to 

 carry a tank along the flue d, and also 

 the smoke-flue in space /, as already 

 alluded to. With such an alteration, we 

 think this would be one of the best pits 

 which has come under our notice. At 

 all events, as constituted by its intelligent 

 author, it is at present deficient in the 

 command of heating power. 



