latter is put into and secured to the steel firebox shell.
To put the copper firebox into place the boiler is lifted by a crane and turned upside down, so that it rests on its back supported on blocks with the bottom of the firebox casing upwards. The copper firebox is then lifted by the crane and gently lowered into the firebox casing. To accomplish this, the foundation ring, which has been placed temporarily in position, will have to be removed. The firebox has to be set by measurement and to the marked centre lines, so that it will occupy an exactly central position. When everything is correct, the firebox and the shell are riveted together through the replaced foundation ring with long rivets, and also at the firehole ring. The roof stay holes in both the firebox and the top of the shell, when direct roof stay bolts are used, are reamered out with long reamers, and the holes are tapped in position for the stay screw threads. The reamering and tapping of screw threads through the plates are done by means of pneumatic drilling machines. These are driven at high speed by compressed air, and are arranged to take drills, reamers, taps, etc., as required. It may here be mentioned that every modern boiler shop is equipped with a complete air-compressing plant, from which pipes are taken to every part of the shop. To a large number of points on these pipes, flexible tubes can be attached to serve pneumatic chipping and caulking hammers, portable drilling machines, etc., so
