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HEATING AS APPLIED IN HORTICULTURE. 



boiler. Hot-water pipes from the same 

 boiler pass along the ends and front of 

 the house b, in the front and end passages. 

 These pipes are very properly laid level 

 with the tanks, which prevents the latter 

 from overflowing. Tubes — c in section — 

 pass up through the bed from the tanks, to 

 admit steam into the house when required. 

 The pipes are open at the extreme ends, 

 and the water makes its return through the 

 cistern c in plan, instead of by an elbow 

 turn, as is usually the case. This is done 

 so that the orifices of the pipes may be 

 easily stopped, to prevent circulation in 

 summer, when little atmospheric heat is 

 required. We would have preferred stop- 

 cocks such as are used in the Frogmore 

 gardens, placed at the ends nearest the 

 boiler. The tanks are also furnished with 

 sluices, d, at the ends of the flow-tanks, 

 by which the heat is regulated. 



General remarks on tank-heating. — The 

 principal objections to the tank mode of 

 heating, (unless the necessary provisions 

 are made,) are an excess of bottom with 

 a deficiency of atmospheric heat, and an 

 excess of humidity when the heat from 

 the tank is admitted freely into the house 

 or pit. On this subject, we find the fol- 

 lowing very sensible remark, in a com- 

 munication from an anonymous corres- 

 pondent in "The Gardeners' Chronicle." 

 " It is well known," he observes, " that 

 by means of a flow and return tank, the 

 degree of bottom heat in pits can be very 

 steadily maintained. Once the mass of soil, 

 or other materials composing the bed, 

 is heated to the required pitch, very little 

 heat is required to keep it up, and sud- 

 den changes of extreme temperature do 

 not greatly affect it. If the temperature 

 outside be one night at 55°, and the next 

 at 25°, this difference of 30° will only 

 occasion a few degrees lower temperature 

 in the soil of the bed. But the case is 

 very different as regards the air of the 

 pit ; for under the above conditions it 

 would certainly be affected to a much 

 greater extent, perhaps as much as 20°. 



" Presuming that the temperature of 

 the bed is exactly what it ought to be, 

 any attempt to counteract the coldness 

 of the air in the pit, in a cold night, will 

 cause an excess of bottom heat, which by 

 repetition must prove highly injurious. If 

 the communication of heat from the tanks 

 to the surface is only through the mass 



of soil, the conduction of heat is exceed- 

 ingly slow, whilst its escape by the glass 

 is rapid. To raise the temperature of 

 the whole mass of soil 10° in as many 

 hours, would require an extraordinary 

 force of fire; notwithstanding which, 

 should a fall of external temperature take 

 place to the extent of 30°, not an unusual 

 circumstance, the top heat will lose 30°, 

 less 10° counteracted by increase of bottom 

 heat ; — or, in other words, the air in the pit 

 will be 20° lower than it ought to be ; and 

 in attempting to prevent this, the bottom 

 heat will be raised 10° too high. If the 

 tanks are in a chamber communicating 

 with cavities between the walls and soil, 

 the external cold will be much more 

 readily counteracted by the increased 

 heat of the tanks ; but if, as presumed, 

 the bottom heat was previously high 

 enough, an excess must be communicated 

 to the soil by any extra heating of the 

 tanks immediately under it. It is evident 

 that, whilst the requisite supply of heat 

 for the bottom is almost uniform, and 

 that for the top is exceedingly variable, 

 both cannot be duly heated by combina- 

 tion. A separate command of heat is 

 necessary for each. A boiler with tanks 

 for bottom heat, and another with tanks" 

 or pipes "for top heat, and the whole 

 so constructed as to admit of giving 

 out moist or dry heat, according as 

 may be required, is doubtless the most 

 perfect arrangement ; and perhaps it 

 might be found ultimately not to be 

 the most expensive." This correspondent 

 proposes to introduce a small steam-pipe, 

 say of 2 inches bore, to rise from the top 



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