BOILERS AND PIPES. 



233 



ject of elaborate calculation, which the 

 imperfections and uncertainties of the 

 practical details render of little value. 

 The following, as a general rule, will be 

 found, perhaps, as good if it were demon- 

 strated by algebraic formulae : — Take the 

 cubic contents of the house, and for half- 

 hardy plants give to every 100 feet 10 

 square inches of boiler surface, and 1 

 square inch of fire grate. For tropical 

 plants, double these proportions ; and 

 for forcing-houses, take intermediate pro- 

 portions according to the temperature 

 required." 2000 feet of pipe-surface is 

 found sufficient to heat the large conser- 

 vatory at Chiswick, containing 100,000 

 cubic feet of capacity, and 1 1,000 square 

 feet of glass. This, with ease, commands 

 a degree of heat 30° above the external 

 temperature. 



Much depends upon the distance that 

 the pipes are apart from each other at 

 their junction with the boiler, as regards 

 the insuring a proper circulation. That 

 distance should not be less than 1 6 inches 

 from centre to centre of 4-inch pipes of 

 ordinary length, where they have not to 

 dip under the level of the top of the 

 boiler. For general purposes, where the 

 boiler is not more than 18 inches deep, 

 it will be better to take the flow-pipe off 

 from the top, and insert the return-pipe 

 as near to the bottom of the boiler as the 

 joining can be safely made. Where the 

 pipes are less than 4 inches, and extend 

 50 or 60 feet from the boiler, with only 

 one turn, the above precaution is of less 

 consequence, as the water will be con- 

 siderably cooled before its return to the 

 boiler. 



The proper size of pipes requires some 

 consideration ; for, at first sight, we might 

 be led to suppose that the main feeding- 

 pipe, which proceeds from the boiler, and 

 has to supply several circulating ones, 

 ought to be of area equal to that of all 

 the circulating pipes together. This, 

 however, is not the case. A 4-inch pipe 

 will serve a supply to four pipes of like 

 diameter; but beyond this number it will 

 be prudent to increase the size of the 

 feeding-pipe, more especially if the cir- 

 culating ones extend to a length exceed- 

 ing 50 or 60 feet; but this increase of 

 size need not exceed the above propor- 

 tion, as the velocity in the main pipe 

 is increased, in proportion to the num- 

 VOL. i. 



ber of branches, to the limits above 

 stated. 



Small pipes should be employed, say 

 of 4-inch diameter at most, when the 

 water is to be conveyed to a distance 

 from the boiler, as in the case of two or 

 more houses being heated at the same 

 time, and at some distance from each 

 other; as a pipe of the above dimensions, 

 while it is sufficient to afford the supply, 

 loses only one-half the heat which a pipe 

 double the size would do, the water flow- 

 ing four times as fast in the former as in 

 the latter case, and the loss of heat in the 

 water being not in proportion to the 

 velocity, but to the length of circuit. 

 Pipes so circumstanced should be laid in 

 an air-tight drain, as air in a stationary 

 state is a powerful non-conductor; or 

 they may be embedded in charcoal, or 

 some other equally non-conducting mate- 

 rial. Indeed, smaller connecting or feed- 

 ing pipes than the above have been 

 successfully employed — even 2-inch pipes 

 to supply 4-inch radiating ones. 



It is not easy to say how far hot water 

 may be carried in pipes enclosed in air- 

 tight drains, but certainly much farther 

 than has yet been attempted. The most 

 proper drain for this purpose is the double- 

 walled barrel, (fig. 313,) or one with up- 

 right sides and circular top, (fig. 314 ;) as 



Fig. 313. 



Fig. 314. 



these, together with the elliptical or egg- 

 shaped, are the strongest of all drains, 

 and have, at same time, the property 

 of throwing off the water from above 

 them. MrAinger, 

 * lg ' ;il in " Gardeners' 



Chronicle," has 

 proposed a square 

 drain or tunnel, 

 with double sides, 

 as in fig. 315 ; 

 and recommends 

 that both ends 

 be open, " the 

 one opening into the atmosphere of 



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