212 VARIOUS METHODS OF HEATING DESCRIBED IN DETAIL. 



plants from being subjected to a high temperature, that are situ- 

 ated in the vicinity of the pipes. In the drawing, (Fig. 43,) 

 the flow and return pipes are placed together, the other side 

 being heated by the flue from the fire. This arrangement is 

 intended to economize heat, and to save the expense of pipes, 

 which, in some places, might be an object of importance, and 

 even if they were not so, the plan is decidedly good. As for the 

 tank, it is an admirable contrivance. Not only is the evil of 

 having highly heated pipes for weeks and months together, 

 directly under the roots of plants, prevented, but when the tank 

 is once heated, a more agreeable and healthy warmth will be 

 produced, and the equilibrium of temperature be maintained 

 for a much longer time. 



The tanks used may either be wooden or metallic. The lat- 

 ter are preferable, both on account of durability and radiation 

 of heat, although wooden ones are much cheaper, and answer 

 the purpose perfectly. Wooden tanks, if the wood be kyanized, 

 or otherwise treated with a metallic solution, will last for many 

 years, and produce a very agreeable warmth. Galvanized iron 

 and zinc are now in common use for this purpose. The dura- 

 bility imparted to it by the process of galvanization, which pre- 

 vents oxidation, is evident from the number of articles made 

 of this material and exposed to the atmosphere. For horticul- 

 tural purposes, this article is likely to become exceedingly 

 useful ; as every one is aware of the injury which ordinary hot- 

 water pipes, and other metallic substances used in horticultural 

 erections, are liable to from rast. Tanks made of this material 

 give out their heat much more rapidly. But it must be consid- 

 ered that the same circumstances that would render them more 

 quickly effectual, would also render their effect more transient. 

 For pits and very small houses, the pipes and tanks might be 

 made of this material. Its cheapness and lightness are impor- 

 tant advantages in its favor; for, when heavy-cast metal pipes 

 are conveyed to a great distance, the cost of carriage will nearly 

 amount to the same sum as would purchase galvanized iron or 

 zinc tanks, and convey them too. 



In using this kind of tanks, the utmost care ought to be 

 taken in supplying them with water. They ought never to be 



