204 STEAM.
ever so careful, when great danger follows; while if the cocks were placed a little higher, the loss of water would not be necessarily followed by so much danger. In a 230. 2. Duties to Machinery when Steam is Getting up.The water in the boiler when the fires are lighted ought to be just above the bottom of the glass. large, or even moderate sized boiler, the water will expand, and there is also not so much water to heat at first; and we know, by reason of conduction and radiation, that small bodies of water are heated comparatively more rapidly than large. On first lighting the fires they should not be kept too large, but just sufficient to cover the bars. large thin surface of fire is found to be the most effective on getting under weigh. A When the fires are lighted, and the steamer is going on a long voyage, it is the practice to rub the polished parts of the engine over with a composition of tallow and white lead. This prevents any rust forming on the rods, etc., from water dropping on them which may have been used for keeping the bearings cool. The discharge valve is also opened now, or else on starting the engine something will give way. Several accidents have. occurred by neglecting to do this. The safety valves are now to be inspected to find out whether they are fast corroded to their seatings. If so, they must be freed and made ready to act before starting. It is a good plan, and one much practised, to give the engines a good blowing through whilst the steam is getting up. This warms the cylinder, and tries any joints that may have been made since the engines were worked last. It also saves the steam, for if not done now (when the engine is starting), a great amount of steam is wasted in heating the cylinder instead of imparting its elastic force to the piston. It is thus that boilers are sometimes taxed beyond their powers, and the steam pressure reduced to perhaps a very dangerous point. 231. 3. Starting the Engines. All ships are now fitted with the double eccentrics, or "Stephenson's Link Motion," by which the engines are started, or rather by this the slide valves are under the command of the engineer, and can be
