76 PRACTICAL FLORICULTURE. 



front. This heat, after it leaves the direct action of the 

 fire, when passing again to the front of the boiler, is called 

 " secondary," and though its power is comparatively 

 slight compared with the direct heat from the fuel to the 

 inner surface, yet it otherwise indirectly benefits, by check- 

 ing the rapid escape of heat out at the chimney, whicli 

 would be the case to a great extent if this back draft was 

 not used. We believe that by using this second heating 

 surface, a saving of one-third in fuel is made. At present 

 prices, a boiler and pipes to heat 1,000 square feet of glass 

 by hot water will cost in this district about $500. Brick 

 flues, to heat the same area, would cost about $100. 



Heating by tanks of hot water was much in use a few 

 years ago, when the grape vine fever was at its height, 

 and is still used by some for propagating purposes ; 

 but our experience, as well as that of many others who 

 have had them in extensive use, is that they are an un- 

 profitable means of heating. Made in the usual way, of 

 wood, we have never known them to be in use over two 

 winters without seriously leaking. If made by lining 

 with zinc, or by having them made of cast-iron, they then 

 cost as much as the regular 4-inch pipe, and are not so 

 durable, and for the heating for any purpose they have no 

 advantage in any respect over them ; four years ago I 

 threw out over 2,000 square feet of wooden tanking, that 

 had leaked so as to become unserviceable in three years, 

 and replaced it by 4-inch pipe. Almost all who have used 

 them have had the same experience. 



