65 



THE ORCHID WORLD. 



silver, followed by copper, brass, cast-iron, 

 wrought-iron, and lead. The great cost of 

 the first three compels us to utilise cast-iron 

 for the construction of the boiler and pipes. 



Although a saving in the cost of the heat- 

 ing apparatus is thus obtained, it must be 

 remembered that the greater the difficulty of 

 transferring the fire-heat to the water, or the 

 heat of the water to the surface of the pipes, 

 the larger will be the amount of fuel con- 

 sumed. With the ever increasing cost of fuel 

 we may, in the near future, have to consider 

 whether it will be more advantageous to 

 spend a larger sum of money in erecting an 

 apparatus composed of some material, such 

 as copper, having a higher power of 

 conductivit}'. 



Radiation, from radio, to emit, or give off, 

 rays. The air, by direct contact, receives a 

 small amount of heat from the hot-water 

 pipes. It is not sufficient for heat to be 

 brought to the surface of the hot-water pipes, 

 it must be radiated, or given off. One may 

 often have heard a remark to the effect that 

 although there are plenty of pipes in the 

 house, which are alw-ays hot, yet the tempera- 

 ture of the air is never as warm as it should 

 be. This is an interesting point. Those who 

 have been up in a balloon, or a flying machine, 

 have noticed that the atmosphere gets colder 

 and colder the further they go away from the 

 earth, yet at the same time they are getting 

 nearer to the sun. This is because the rays 

 of heat always pass through the air without 

 affecting it ; it is only when they come in 

 contact with heat absorbing substances that 

 these bodies are gradually made warm. The 

 air IS warmed by direct contact with these 

 heated bodies. 



It will, therefore, be seen that it is abso- 

 lutely necessary for the pipes to give off rays 

 of heat which, when coming in contact with 

 heat absorbing materials in the house, will 

 warm them ; these warmed objects will then 

 warm the air in direct contact with them. 



Now this radiation does not depend on the 

 material of the pii>es, but entirely on the 

 nature of their outer surface or skin. If the 

 pipes were made of silver, a metal of high 

 conductive but low radiative power, they 



would, when feeling e.xtremel\- liot, radiate 

 or give off very little heat. If these silver 

 pipes were polished still less heat would be 

 obtained from them. This is because silver 

 is a bad radiating material. Lamp black is 

 one of the very best and most suitable radi- 

 ating materials. If the silver pipes are coated 

 with this substance we lia\e the finest 

 conductive material radiating, or giving ofl, 

 heat in a very efficient manner. 



Cast-iron pipes come very near to those 

 of silver, but even with these a great deal 

 will depend on whether the surface is rough 

 or polished. If m the latter state poor 

 results are bound to occur, but if coated with 

 lamp black the radiating power will be 

 greatly increased, and a corresponding rise 

 in the temperature of the house will be 

 produced. 



Therefore, it will be plainl\- seen that in 

 order to allow the heat of the water to mani- 

 fest itself on the outside of the pipes these 

 must be made of a material having a high 

 conductive power ; and secondly, the surface 

 of these pipes must be in a suitable radiating 

 condition or the heat will not be given off into 

 the house. 



Convection (from conveho, to carry up). 

 Water is a fairly good conductive substance, 

 but it is almost impossible for the heat to 

 pass through a long length of pipe. Resource, 

 is, therefore, taken of the difference in the 

 weight of hot and cold water. The idea that 

 hot-water always ascends is incorrect. It is 

 the cold water which, being heavier, sinks to 

 the lowest part and so forces the hot-water 

 to the highest portion of the heating appar- 

 atus. If the pipes are placed on a continual 

 rise the hot-water will gradually pass through 

 them in reaching the highest point. When 

 parting with its heat it becomes heavier and 

 again returns to the boiler. It is thus that 

 the circulation is maintained. 



Convection is also in evidence in the atmo- 

 sphere. As soon as the air is warmed by 

 contact with a heated body it rapidly ascends, 

 its place being occupied by air of a lower 

 temperature. The circulation of air takes 

 place at a much more rapid rate than that 

 of water. G. W. 



