another.  The preferable arrangement appears to be, to cast upon each blow-off cock a bend for attaching the cock to the bottom of the boiler, and the plug should stand about an inch in advance of the front of the boiler, so that it may be removed, or re-ground, with facility.  The general arrangement of the blow-off pipes is to run a main blow-off pipe beneath the floor plates, across the ship, at the end of the engines, and into this pipe to lead a separate pipe, furnished with a cock, from each boiler.  The main blow-off pipe, where it penetrates the ship’s side, is furnished with a cock:  and in modern steam vessels Kingston’s valves are also used, which consist of a spindle or plate valve, fitted to the exterior of the ship, so that if the internal pipe or cock breaks, the external valve will still be operative.  Some expedient of this kind is almost necessary, as the blow-off cocks require occasional regrinding, and the sea cocks cannot be re-ground without putting the vessel into dock, except by the use of Kingston’s valves, or some equivalent expedient.

472.  Q.—­What is the proper construction and situation of the injection cocks, and waste water valves?

A.—­The sea injection cocks are usually made in the same fashion as the sea blow-off cocks, and of about the same size, or rather larger.  The injection water is generally admitted to the condenser by means of a slide valve, but a cock appears to be preferable, as it is more easily opened, and has not any disposition to shut of its own accord.  In paddle vessels the sea injection pipes should be put through the ship’s sides in advance of the paddles, so that the water drawn in may not be injuriously charged with air.  The waste water pipe passing from the hot well through the vessel’s side is provided with a stop valve, called the discharge valve, which is usually made of the spindle kind, so as to open when the water coming from the air pump presses against it.  In some cases this valve is a sluice valve, but the hot well is then almost sure to be split, if the engine be set on without the valve having been opened.  The opening of the waste water pipe should always be above the load water line, as it will otherwise be difficult to prevent leakage through the engine into the ship when the vessel is lying in harbor.

473.  Q.—­What is the best arrangement of gauge cocks and glass gauges?

A.—­Gauge cocks are generally very inartificially made, and occasion needless annoyance.  They are rarely made with bottoms, or with stuffing boxes, and are consequently, for the most part, adorned with stalactites of salt after a short period of service.  The water discharged from them, too, from the want of a proper conduit, disfigures the front of the boiler, and adds to the corrosion in the ash pits.  It would be preferable to combine the gauge cocks appertaining to each boiler into a single upright tube, connected suitably with the boiler, and the water flowing from