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24 case of steel tubes a ridge or beading is also rolled on the tube on the boiler side of the firebox tubeplate. Brass or copper tubes are expanded and secured by driving short pieces of steel tube (called ferrules) tightly into the ends which pass through the tubeplate. At the smokebox end the tubes are merely expanded, neither beading nor ferrules being used.

Mountings. The boiler is then sent to another part of the shop to have the “mountings” put on. This term includes all the brass and other fittings, such as safety valves, water and steam gauges, cocks, etc. In British practice the mountings are not screwed directly into the boiler plates. Steel “pads” or seatings of the same shape as the flanges of the mountings having been previously riveted to the boiler, the flanges are secured to these by studs. The joints are faced and scraped, and either made metal to metal with boiled linseed oil, or a thin sheet of asbestos slightly smeared with red lead is placed between the faces. The nuts are then tightened gradually to make an absolutely steam-tight joint.

Boiler Testing. The boiler before it leaves the shops undergoes two tests. The first is a hydraulic test up to a pressure from 25 to 50 per cent. higher than the pressure at which the boiler works in service. The safety valves are locked, the boiler filled up with water, and the necessary pressure obtained by forcing additional water