Some convenient ar rangment, such as a cord or lever, should be fitted to a safety-valve, so that it can readily be opened by hand; and the valve should be moved at least once a day, to keep it in good working order. A simple experiment to determine whether or not the valve is in truth a safety valve can readily be made by every steam-user. It will only be necessary to shut off the steam from the engine, or wherever else it is used, and making up a good fire in the boiler, observe whether the pressure increases materially beyond the point for which the valve is set. This experiment can be made without the slightest danger, since, if the valve will not relieve the boiler automatically, it can be opened to any desired extent by hand. Anyone can readily perceive the importance of making this test, for with a good safety-valve in working order, the chances of a disastrous boiler explosion are greatly diminished. 13.