The spreading system is most commonly employed in the Western States, where the coal contains a great deal of clinker. When this is practiced, the coal is spread evenly over the whole of the grate in a thin layer, and its success and economy depend upon the regularity and evenness with which this layer of coal is maintained and the fire fed. The thickness of the coal must be adapted to the working of the engine. When it is working lightly, the layer of coal should be thin, but when the engine is pulling hard the layer of coal must be thicker, otherwise the violent blast may lift the coal off the grates. The success of this system, as was explained in answer to Question 388, depends upon the manner in which the thickness of the fire is regulated, on the admission of the proper amount of air above the fire, and on the frequency with which the fire is supplied with coal. When this system of firing is employed not more than two shovels-full of coal should be put into the fire-box at once, and if the engine is not working hard, one or even less will be sufficient. The firemen must, however, determine by experience the thickness of fire, amount of air which should be admitted and the frequency of firing which will give the best results in practice. Doubtless these will vary with different kinds of fuel and the construction of engines. Usually the greatest obstacle in the way of producing good results is the fact that firemen would rather “take things easy” than exercise that diligence and observation which will alone insure success in any occupation. QUESTION 496. _How can smoke be most effectually prevented?_ _Answer._ The means of preventing smoke were very fully explained in answer to Questions 379 and 388. It may be said briefly that this can be done only by properly regulating the supply of air which is admitted to the fire. The means of doing this have already been explained. QUESTION 497. _What method of firing is employed when anthracite coal is used?_ _Answer._ The spreading system alone is then used. QUESTION 498. _How may the rules which firemen should observe when bituminous coal is used be briefly stated?_ _Answer._ 1. Keep the grate, ash-pan and tubes clean. 2. Break the coal into small lumps. 3. Fire often and in small quantities. 4. Keep the furnace door open as little as possible. 5. Consult the steam gauge frequently, and maintain a uniform steam pressure, and if necessary to reduce the pressure do it by closing the ash-pan dampers rather than by opening the furnace door. QUESTION 499. _On arriving at a station where a train stops longer than a few minutes, what should the locomotive runner and fireman attend to?_