_Answer._ If a steam-chest is broken a block of wood should be bolted over the mouth of the steam passage, so as to prevent the escape of the steam from the steam-pipe on that side. It will sometimes require considerable ingenuity to devise means of fastening such a block or blocks of wood so as to cover the mouth of the steam passage. As cylinders are now usually made, the blocks can be fastened by cutting them to the proper form and size, and then placing a thick block on top, and bolting the steam-chest cover down on top of it. If the cover is broken, a part of it may be used or a piece of plank with a few holes bored into it be employed instead. In some cases a piece of board can be bolted over the end of the steam-pipe. When the latter is broken, it should be taken down and a piece of board or plank bolted over the opening of the ~⊤~-pipe to which the steam-pipe was attached. The engine can then be run with one cylinder as before, although usually in such cases it is not necessary to disconnect any other parts than the valve stem. QUESTION 521. _What must be done if a piston, cross-head, connecting-rod or crank-pin is broken or bent?_ _Answer._ If the piston, cross-head or main connecting-rod is broken, the same course must be pursued as when a cylinder is broken. If a coupling-rod or a crank-pin of a trailing-wheel is broken, then it is necessary to take down both the coupling-rods, but not to disconnect the main connecting-rods or their attachments, unless they are injured. QUESTION 522. _If one coupling-rod is broken or taken down, why must the other be taken down also?_ _Answer._ Because if only one rod is used there is then nothing to help the cranks of the trailing wheels past the dead-points, so that in starting, or if they are moving slowly when they reach these points, they are quite as likely to revolve in one direction as the other. If they happen to turn in the reverse direction to that in which the wheels to which they are coupled are moving, then the crank-pins of one or the other pair of wheels are very liable to be broken or bent. QUESTION 523. _What must be done if a driving-wheel tire or driving-axle breaks?_