obtained, thus giving about 60 per cent. efficiency, while 40 per cent. of
the heating power is unavoidably lost. But with petroleum an evaporation
of 12.25 lb. is practically obtained, giving 12.25/16.2 = 75 per cent.
efficiency. Thus in the first place petroleum is theoretically 33 per
cent. superior to anthracite in evaporative power; and secondly, its
useful effect is 25 per cent. greater, being 75 percent. instead of 60
percent.; while, thirdly, weight for weight, the practical evaporative
value of petroleum must be reckoned as at least from (12.25 - 7.50)/7.50 =
63 per cent. to (12.25 - 7.00)/7.00 = 75 per cent. higher than that of
anthracite.

_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 ½ mm. to 2