A Correspondent at Washington, D. C, writes: "I am Figuring on a greenhouse job and want to run my pipes in accordance with the annexed sketch. Will the arrangement work? C is a 100-foot coil under a hot-bed, and it must be supplied from the main A on the other side of the path P without obstructing the passageway. This coil is the last at the end of pipe A.

"I think it would circulate all right by going over the walk and having another bend around under it as shown. The main A is higher up than the branch to the coil. If this will not work, what would you suggest ?"

[The lower loops D, J, K, K are unnecessary. The arrangement will circulate through the upper loops D, E, G, H if the air be prevented from collecting there. This can be readily done by connecting a vent pipe E L to reach up above the expansion tank and open at the top. This can be the more easily done since in a greenhouse system the tank is rarely very much elevated.]