of 8 atm.—­120 lb.—­is thus obtained in fifty to fifty-five minutes from the time the spray jet was first started.  In daily practice, when it is only necessary to raise steam in boilers already full of hot water, the full pressure of 7 to 8 atm. is obtained in from twenty to twenty-five minutes.  While experimenting with liquid fuel for locomotives, a separate tank was placed on the tender for carrying the petroleum, having a capacity of about 3 tons.  But to have a separate tank on the tender, even though fixed in place, would be a source of danger from the possibility of its moving forward in case of collision.  It was therefore decided, as soon as petroleum firing was permanently introduced, to place the tank for fuel in the tender between the two side compartments of the water tank, utilizing the original coal space.  For a six-wheeled locomotive the capacity of the tank is 3-1/2 tons of oil—­a quantity sufficient for 250 miles, with a train of 480 tons gross exclusive of engine and tender.  In charging the tender tank with petroleum, it is of great importance to have strainers of wire cloth in the manhole of two different meshes, the outer one having openings, say, of 1/4 in., the inner, say 1/8 in.; these strainers are occasionally taken out and cleaned.  If care be taken to prevent any solid particles from entering with the petroleum, no fouling of the spray injector is likely to occur; and even if an obstruction should arise, the obstacle being of small size can easily be blown through by screwing back the steam cone in the spray injector far enough to let the solid particles pass and be blown out into the fire-box by the steam.  This expedient is easily resorted to even when running; and no more inconvenience arises than an extra puff of dense smoke for a moment, in consequence of the sudden admission of too much fuel.  Besides the two strainers in the manhole of the petroleum tank on the tender, there should be another strainer at the outlet valve inside the tank, having a mesh of 1/3 in. holes.

Driving locomotives.—­In lighting up, certain precise rules have to be followed, in order to prevent explosion of any gas that may have accumulated in the fire box.  Such explosions do often take place through negligence; but they amount simply to a puff of gas, driving smoke out through the ash-pan dampers, without any disagreeably loud report.  This is all prevented by adhering to the following simple rules:  First clear the spray nozzle of water by letting a small quantity of steam blow through, with the ash-pan doors open; at the same time start the blower in the chimney for a few seconds, and the gas, if any, will be immediately drawn up the chimney.  Next place on the bottom of the combustion chamber a piece of cotton waste, or a handful of shavings saturated with petroleum and burning with a flame.  Then by opening first the steam valve of the spray injector, and next the petroleum valve gently, the very first spray of oil coming on the