158 



HEATING AS APPLIED IN HORTICULTURE. 



opening for filling the apparatus with 

 water. This opening in the expansion- 

 pipe is placed near to its lowest extremity, 

 and when the pipes are charged with 

 water, this aperture is secured with a 

 strong screw. The expansion-pipe is 

 capable of containing 1-1 2 th as much 

 water as is contained in the whole of the 

 smaller pipes. The greatest care must 

 be taken that this pipe be kept empty, else 

 the expansive force of the heated water, 

 which is irresistible, would burst the pipes. 



To show the power of this apparatus, 

 we may mention that the average heat of 

 the pipes is in general 350°, which is equal 

 to a pressure of 135 lb. per square inch, 

 and that in different parts of the pipe 

 there has been found a variation of tem- 

 perature amounting to 200° or 300°. This 

 variation is owing both to the intensity 

 of heat in the furnace, and also to the 

 proportion the surface of the coil-pipes 

 bears to the surface of the radiating ones. 

 The variation in temperature has been 

 observed to amount to from 220° to 550°, 

 the latter being equal to a pressure on 

 the pipes of 1100 lb. per square inch, 

 or upwards of 71 atmospheres. " It may 

 be admitted," says Bernan, in " History 

 of Heating," &c, "that the hazard of 

 bursting is nearly relative ; for as Mr 

 Perkins proves his pipes, when cold, to 

 resist a pressure of 2800 lb. per inch, 

 there may be, and perhaps is, less danger 

 in working his apparatus at a pressure of 

 1100 lb. on the inch, than a Trevithic 

 engine working under 50 lb. on the inch. 

 We know, however, from experience, that 

 from use the material of the pipes loses 

 its original tenacity, and that pipes which 

 have, when cold, resisted the pressure 

 stated by Mr Perkins, when heated, have 

 given way even below the temperature at 

 which they had long been worked with 

 safety. The fear of danger, if its actual 

 presence in the average of cases be dis- 

 puted, is no doubt greatly increased by 

 the knowledge that no method has been 

 devised to regulate the pressure in the 

 sealed pipes, like the safety-valve of a 

 steam-engine, nor any means to prevent 

 a careless attendant on the furnace at 

 any time endangering the safety of the 

 apparatus. In many cases the high tem- 

 perature of the pipes is objectionable, 

 from surfaces at 300° or 400°, rendering 

 the air insalubrious by decomposing the 



animal and vegetable matters suspended 

 in it. On this account a high-pressure 

 pipe is not superior to a German stove, 

 whose surface is generally about 300° ; 

 and a pipe at this temperature cannot be 

 placed without danger near combustible 

 materials." 



The maximum pressure in high-pres- 

 sure steam-boilers is only from 45 to 48 

 lb. per square inch, while the pressure 

 on the coil of pipes in this system varies 

 from 10 to 24 times that amount, accord- 

 ing to the intensity of heat in the furnace. 

 " As there are no means of regulating the 

 temperature in hermetically-sealed pipes, 

 so there can be none for limiting the 

 pressure which they sustain." The appa- 

 ratus may to all appearance be perfectly 

 safe at the time of inspection, and, in a 

 few months afterwards, if in the hands of 

 unskilful or careless people, it may be 

 exceedingly dangerous. The coil-pipes, 

 being at all times exposed to such an 

 intense heat, will become thinner and 

 thinner, until they give way at last, when 

 the consequences may be disastrous. 

 While we are quite sensible of the great 

 ingenuity of this invention as a most 

 powerful heater, we are equally alive to 

 the danger attending it ; and therefore we 

 would never think of applying it to hot- 

 house heating. The small size of the 

 pipes, and the facilities they afford of 

 being placed behind skirting-boards, and 

 conveyed under floors in dwelling-houses 

 and public buildings, have rendered this 

 system popular amongst house architects. 

 It would be well for them, however, to 

 consider how far they place in jeopardy 

 of fire the buildings into which they in- 

 troduce pipes heated to upwards of 400°, 

 and placed amongst combustible mate- 

 rials. These considerations have led us to 

 enter more fully into the merits of the 

 system than we had originally intended. 



The four following diagrams from 

 Bernan's " History of Heating and Ven- 

 tilation," will more clearly explain Per- 

 kins' principle. In fig. 169, "A coil of 

 wrought-iron pipe of small diameter, 

 placed in a furnace a, is continued and 

 conducted through the building, and the 

 necessary quantity of surface is given by 

 forming coils n of the pipe, which are 

 placed in the rooms or spaces to be 

 heated ; and the pipe is finally returned, 

 as at s, into the furnace, where it is joined 



