t% The Sweet Potato 



steam or hot water is employed than where other meth- 

 ods of supplying heat are used. 



" When steam or hot-water pipes are used to heat 

 the hotbed, the best results are secured when the pipes 

 are placed near the bottom of the hotbed pit, the soil 

 being put on a tile or board floor resting on pipe or 

 wooden supports so as to leave a space of a few inches 

 between the bottom of the pit and the floor. The num- 

 ber and size of the heating pipes required depend on 

 the rapidity of the circulation and on the temperature 

 of the water or the pressure of the steam. When hot 

 water is used, four 1%-inch pipes will be ample in 

 most cases for beds not over 50 feet long. For larger 

 beds 2-inch pipes should be used. Two of the pipes 

 serve as flow pipes and two as returns. The water 

 enters at one end, makes the circuit of the bed, and 

 leaves at the same end. The point where the pipes 

 enter the bed should be the highest in the system, and 

 the point where the pipes leave the bed the lowest in the 

 system. The pipes should have a unifonn grade and 

 should be evenly spaced, with the flow pipes about a 

 foot from each outside wall and the returns in the 

 middle. When steam is employed the arrangement of 

 the bed and pipes is the same, but smaller pipes may be 

 used. With steam at 10 pounds pressure 1-inch pipes 

 are large enough for 50-foot beds, and 1^-inch pipes 

 are ample for beds up to 100 feet long." 



A general idea of the construction of a pipe-heated 

 bed may be gained from Fig. 7. The same rules gov- 

 erning greenhouse heating apply to piping beds of this 

 kind. 



