The cylinders of locomotives in this country are now universally placed on the outside of the wheels, as has already been described. In order to fasten them securely together and to the boiler, they are attached to what is called a _bed-plate_ or _bed-casting_, _D D_, figs. 94 and 95, which is placed between them. Some builders make this bed-casting in a separate piece, and the cylinders are then bolted to it on the outside, about at the dotted lines, _l_, _m_, fig. 95. Others cast one-half of it with each cylinder, as shown in our engravings, and then bolt them together at the line _i_, _j_, which is the centre of the engine. The bed-casting is also bolted to the smoke-box by the flanges _E_, _E_. The cylinders are bolted to the frame _F_ with bolts, _m_ and _k_, fig. 95. After the cylinders are bored out, and the ends turned off, _heads_, _A_ and _B_, figs. 92 and 94, are fitted with steam-tight joints to each end. These heads are fastened with bolts and nuts, _a_, _a_, _a_, to flanges, _C_, _C_. QUESTION 160. _How is the steam conducted to and from the cylinders?_ _Answer._ Two pipes or passages are cast in each cylinder, the one, _G G′_, fig. 95, for admitting steam into the steam-chest, and the other, _H H′_, for exhausting it from the cylinders. The one _G G′_ is called the _steam-passage_, and the other, _H H′_, the _exhaust-passage_. The steam-passage terminates at one end with a round opening, _G_, figs. 94 and 95, to which the steam-pipe _o_, figs. 40 and 95, is attached inside of the smoke-box. At the other end it divides into two branches, _G′_, _G′_, fig. 94, each of which terminates in an opening, _g_, _g′_, inside of the steam-chest. The steam is thus delivered at both ends of the chest, and can pass freely into each of the steam-ports. By making the cylinders in this way, they are exactly alike for each side of the engine, or, to use a shop phrase, there are “_no rights and lefts_,” so that a cylinder casting can be used for either side of the engine. This method of making cylinders has been adopted by a number of the principal builders in this country, but is by no means universal. [Illustration: Fig. 92. Scale ³⁄₄ in. = 1 foot.] [Illustration: _Fig. 93._] [Illustration: Fig. 94. Scale ³⁄₄ in. = 1 foot.] [Illustration: Fig. 95. Scale ³⁄₄ in. = 1 foot.] QUESTION 161. _How is the steam-chest constructed?_ _Answer_. It usually consists of two castings, one of which, _J_, figs. 92 and 94, is a square cast-iron box made open at the top and bottom. This rests on the top of the cylinder casting and is joined to the latter with a steam-tight joint. On top of it is a cast-iron cover, _K K_. The steam-chest and cover are held down by bolts, _p_, _p_, which are screwed into the cylinder casting and have nuts on top. QUESTION 162. _How are the slide-valves made to work steam-tight on the valve-seats?_