_Answer._ By oil-cups attached to the straps, above the journals, similar to the cups used on the _guide-rods_, but which are not shown in the engravings of the connecting-rods. Sometimes _oil-cellars_, as they are called, are attached to the under side of the straps. These are metal boxes, which are filled with oil, which is agitated violently by the rapid motion of the rods, and is thus applied to the journals through holes drilled in the straps. In order to confine the oil and prevent its leaking out around the journals of the coupling-rods, the brasses at _n_, _n_, fig. 99, are usually made so as to enclose the outside end of the crank-pin, which thus not only keeps the oil in, but excludes the dust. The brasses are usually lined with Babbitt’s or some other kind of soft metal, which is thought to be less liable to heat from the friction of the journals. QUESTION 180. _Are the coupling-rods always made with stub-ends?_ _Answer._ No; their ends are sometimes made in one piece--that is, without straps or keys. The holes which receive the crank-pins then have brass rings or _bushings_, as they are called, which fit tightly and are driven into the holes, and form the bearings on the pins. When these rings become worn they are driven out and new ones put in. QUESTION 181. _What is meant by the term lost motion?_ _Answer._ It is used to designate the wear of machinery, which causes a loss of motion in some of the parts. Thus if the bearings of the main connecting-rods are worn, the piston must move a distance equal to the wear at each end of the stroke before it moves the crank-pin. Lost motion might therefore be called the looseness of the parts. When we speak of _taking up_ the lost motion, we mean making parts which were loose fit tightly. PART XI. THE VALVE-GEAR. QUESTION 182. _What is meant by the valve-gear of a locomotive?_ _Answer._ By the valve-gear is meant the arrangement of eccentrics, rods, links, rockers, etc., by which the valves are moved and their motion regulated. QUESTION 183. _What is required of the valve-gear in working a locomotive?_ _Answer._ It must be so arranged that the locomotive can be run either backward or forward, and so that the motion of the wheels can be reversed quickly and with certainty. It should enable the runner to employ the greatest power of the engine by admitting steam into the cylinders during the whole or nearly the whole of the stroke of the pistons, or when less power is required, to use the steam more economically by working it expansively, which latter is accomplished with the present appliances by changing the travel of the valve. QUESTION 184. _How is the valve-gear constructed so as to run the engine either backward or forward?_ _Answer._ As already explained, in answer to question 76, two eccentrics are provided for each cylinder. These are set so that one of each pair will run the locomotive in one direction, and the other two the reverse way.