_Answer_. It is intended to carry a supply of dry sand, which is scattered on the rails in front of the driving-wheels when the latter are liable to slip. This is done by two pipes, _e′, e′_, plate I, one on each side of the engine. They lead from the sand-box to within a few inches of the rail. At the upper end and inside the sand-box they each have a valve which is operated by a lever which is connected to the cab by a rod which enables the locomotive runner to open or close the valve at pleasure. The sand-box is usually made of sheet iron with a cast iron base, and a top of a more or less ornamental design. It also has an opening on top through which the sand is supplied to the box. This opening has a loose cover to exclude rain and dirt from the sand. The sand-box is usually located on top of the boiler in front of the front driving-wheels. QUESTION 326. _What is the bell U for?_ _Answer_. It is used for giving signals of the starting or approach of the engine. It also is located on top of the boiler and is usually hung on a cast iron frame and rung with a rope connecting it with the cab. QUESTION 327. _What is the weight of an ordinary locomotive bell?_ _Answer_. From 50 to 100 pounds. QUESTION 328. _What is a locomotive head-light?_ _Answer_. It is a large lamp, _T_, plates I and II, placed in front of the locomotive to signal its approach at night and also to illuminate the track for the locomotive runner. [Illustration: _Fig. 198._ Scale 1¹⁄₂ in. = 1 foot.] QUESTION 329. _How is a head-light constructed?_ _Answer_. The lamp has what is called an Argand burner; that is, a burner with a hollow cylindrical wick, through the centre of which a current of air circulates, which thus supplies the flame with a larger quantity of air than is possible if the latter can come in contact with the former only from the outside. The result is that the combustion is much more brilliant than with ordinary burners. In order to throw all the light on the track the burner is placed inside of a concave reflector, _a b c_, fig. 198, which is of a _parabolic_ form. One of the peculiarities of this form of reflector is that if a light is placed in its focus _f_ the rays will be reflected from its surface in parallel lines. Thus, let _a b c_, fig. 198, represent a section of such a reflector. Now, if a light be placed in the focus _f_ the rays will strike against the reflector, be thrown in the direction of the dotted lines _f 1 x, f 2 x ... f 9 x_, etc., and thus be thrown directly in front of the engine. The reflectors are usually made of copper and plated with silver. The lamps and reflectors for head-lights are inclosed in a rectangular case which is supported on two brackets bolted to the front of the smoke-box. On these brackets a wooden shelf is fastened on which the head-light rests. QUESTION 330. _What are the running-boards and hand-rails?_