official tables to be available for the purpose of continuous steaming at 10-knot speed, as the consumption for auxiliary purposes varies from about 5 to 8 tons a day.
It will readily be understood that the supply and economy of coal on board a fighting ship are matters of the very utmost importance, and any contrivances tending to facilitate them are of great value, but it is probably less well known that the health and efficiency of modern marine boilers depend very largely on there being no stint in the supply of fresh water for them. Such, however, is the case. Any appreciable admixture of raw sea water is fatal to the delicate constitutions of boilers working at a pressure of 155 lbs. on the square inch. Hence special arrangements have to be fitted for making up the necessary waste of fresh water that must occur during a voyage of very moderate length. Theoretically, if machines were perfect, the fresh water taken in from the shore, converted into steam in the boilers, and reconverted into fresh water by the surface condensers, would not diminish in quantity and might go back to the boilers from week's end to week's end on its round of profitable employment. But, in practice, what with unavoidable leaky joints and occasional escapes of steam at the safety valves, it is found that there is a deficit of hundreds of gallons of water every day, which has to be made up. To this end all ships are now fitted with distilling apparatus, or 'evaporators' as they are generally called, for the purpose of converting salt water into fresh, not only for the use of the
