_Answer._ 1. The height of the water in the boiler should always be maintained so as to cover the heating surfaces. 2. The boiler should be kept as clean, that is, as free from scale, mud and other impurities, as possible. 3. It should never be subjected to strains from sudden heating or cooling. 4. The steam-gauge and safety-valves should be examined and tested frequently, to be sure they are in order; and 5, they should examine every part of the boiler which is accessible, but especially the stay-bolts, to see that there is no fracture of any part or any injurious corrosion or other dangerous defect. QUESTION 514. _What should be done in case of the bursting or collapse of a tube?_ _Answer._ As soon as possible after it occurs, the runner must stop the train, and close first the end of the flue in the fire-box, and then that in the smoke-box, by driving in _iron plugs_, which are usually provided for the purpose. These plugs are attached to the end of a bar, with which they are inserted into the tubes. If the escape of water and steam from the tube is so great as to make it difficult to see the end of the tube, the steam may sometimes be drawn up the chimney by starting the blower. If, however, the escape is so great as to make it impossible to insert the plug, then the steam pressure must be reduced by running with both pumps on, or by starting the injector; or it may be necessary to draw the fire and cool off the engine. When a flue collapses, the front end of which is behind the steam or petticoat pipes, it is usually necessary to cool off the engine before a plug can be inserted, especially if any considerable amount of water and steam escape from it. While driving in the plug, the runner and fireman should always keep themselves in such positions that the plug can not hit them in case it is blown out by the steam. If the engine is not supplied with iron flue-plugs, a wooden plug can be cut of the proper size and driven in. This can be attached to the bar referred to and inserted; but if no such bar is carried with the engine, the wooden plug can be made on the end of a long pole and then cut nearly off. It is then inserted into the flue and driven in and broken off. It will be found that such plugs will burn off even with the end of the flue, but will not burn entirely out. QUESTION 515. _What should be done in case a bolt, stud or rivet blows out of the boiler and thus allows the steam or hot water to escape?_ _Answer._ If it is accessible, cut a plug on the end of a long pole and drive it in in the same way as described above. This will avoid the necessity of cooling off the engine; but in some cases it will be found that a plug can not be inserted or driven in without drawing the fire and cooling off the boiler. QUESTION 516. _In case it is found necessary to draw the fire and cool off the boiler, and if so much water has escaped as to uncover the crown plate, what must be done?_