Now take a sheet of copper and cut a piece about six inches and a quarter long by six inches broad, and bend it over a wooden roller to the shape shown at [Fig. 12], keeping it an inch and a half apart between A B. Cut also two other pieces of copper to the shape of your bent sheet ([Fig. 12]), and make it long enough to reach to the dotted line. These form the two ends, which may be placed an eighth of an inch from the edges, as in [Fig. 13], and soldered in place, and the projecting rims turned over and sweated with solder from the outside in the same manner as you did to the boiler-ends in [Fig. 11]. Then drill a three-quarter-inch hole at B ([Fig. 13]) for the bottom of chimney-tube to go into, and cut a piece of three-quarter-inch brass tubing of sufficient length to pass out at top of boiler about half an inch, as shown at A ([Fig. 10]). You can then hammer out a rim or flange on the bottom end of chimney-tube, and push it up through the hole in the copper box and solder it in place from the top, as at A ([Fig. 14]).
Now drill a couple of small holes at each end of the box B C ([Fig. 14]); these should be rather more than an eighth of an inch in diameter, to allow an eighth of an inch tube to pass through.
Get two twelve-inch lengths of hard-drawn steam-piping of an eighth of an inch in diameter, and with your screw-plate put a thread on each end of about half an inch in length, then drill some holes in any odd piece of brass plate, and with the screw-taps form eight nuts to fit the threads on the piping, and finish them up to shape with a file.
Fig. 15.
Then take the piping and bend it very gently, to prevent it cracking, round a bar of iron or handle of some tool held in the vice until it is of the form shown at [Fig. 15]. Do each one the same, and then mix a little turps with some white lead and smear each end where you have formed the screws, taking care not to get any into the tubes, and they might have a plug of paper put in temporarily to prevent it.
Fig. 16.
Now put a nut on at either end as far as the thread will allow it, and smearing a little white lead round the holes drilled in ends of box B C ([Fig. 14]), push the tubes in from the inside and screw up firmly with the remaining nuts in the position shown at [Fig. 16]. The inside nuts can then be tightened up with a spanner, and if you have carefully done this you will never be troubled with any leakage, no matter what pressure you may get in the boiler.
These tubes are immensely strong, and from their small size the water in them is raised quickly to a higher temperature than that contained in the rest of the boiler, causing a continual circulation to take place and a constant supply of steam to be formed.