Spray injector.—­Steam not superheated, being the most convenient for injecting the spray of liquid fuel into the furnace, it remains to be proved how far superheated steam or compressed air is really superior to ordinary saturated steam, taken from the highest point inside the boiler by a special internal pipe.  In using several systems of spray injectors for locomotives, the author invariably noticed the impossibility of preventing leakage of tubes, accumulation of soot, and inequality of heating of the fire box.  The work of a locomotive boiler is very different from that of a marine or stationary boiler, owing to the frequent changes of gradient on the line, and the frequent stoppages at stations.  These conditions render firing with petroleum very difficult; and were it not for the part played by properly arranged brickwork inside the fire box, the spray jet alone would be quite inadequate.  Hitherto the efforts of engineers have been mainly directed toward arriving at the best kind of “spray injector,” for so minutely subdividing a jet of petroleum into a fine spray, by the aid of steam or compressed air, as to render it inflammable and of easy ignition.  For this object nearly all the known spray injectors have very long and narrow orifices for petroleum as well as for steam; the width of the orifices does not exceed from 1/2 mm. to 2 mm. or 0.02 in. to 0.08 in., and in many instances is capable of adjustment.  With such narrow orifices it is clear that any small solid particles which may find their way into the spray injector along with the petroleum will foul the nozzle and check the fire.  Hence in many of the steamboats on the Caspian Sea, although a single spray injector suffices for one furnace, two are used, in order that when one gets fouled the other may still work; but, of course, the fouled orifices require incessant cleaning out.

Locomotives.—­In arranging a locomotive for burning petroleum, several details are required to be added in order to render the application convenient.  In the first place, for getting up steam to begin with, a gas pipe of 1 inch internal diameter is fixed along the outside of the boiler, and at about the middle of its length it is fitted with a three-way cock having a screw nipple and cap.  The front end of the longitudinal pipe is connected to the blower in the chimney, and the back end is attached to the spray injector.  Then by connecting to the nipple a pipe from a shunting locomotive under steam, the spray jet is immediately started by the borrowed steam, by which at the same time a draught is also maintained in the chimney.  In a fully equipped engine shed the borrowed steam would be obtained from a fixed boiler conveniently placed and specially arranged for the purpose of raising steam.  In practice steam can be raised from cold water to 3 atm. pressure—­45 lb. per square inch—­in twenty minutes.  The use of auxiliary steam is then dispensed with, and the spray jet is worked by steam from its own boiler; a pressure