These was another kind of marine engine that I think should not be
passed over without notice; I allude to Howard's quicksilver engine.
The experiments with this engine were persevered in for some
considerable time, and it was actually used for practical purposes in
propelling a passenger steam-vessel called the Vesta, and running
between London and Ramsgate. In that engine the boiler had a double
bottom, containing an amalgam of quicksilver and lead. This amalgam
served as a reservoir of heat, which it took up from the fire below
the double-bottom, and gave forth at intervals to the water above it.
There was no water in the boiler, in the ordinary sense of the term,
but when steam was wanted to start the engine, a small quantity of
water was injected by means of a hand-pump, and after the engine was
started, there was pumped by it into the boiler, at each half
revolution, as much water as would make the steam needed. This water
was flashed on the top surface of the reservoir in which the amalgam
was confined, and was entirely turned into steam, the object of the
engineers in charge being to send in so much water as would just
generate the steam, but so as not to leave any water in the boiler.
The engines of the Vesta were made by Mr. Penn, for Mr. Howard, of
the King and Queen Ironworks, Rotherhithe. Mr. Howard was, I fear, a
considerable loser by his meritorious efforts to improve the
steam-engine.
There was used, with this engine, an almost unknown mode of obtaining
fresh water for the boiler. Fresh water, it will be seen was a
necessity in this mode of evaporation. The presence of salt, or of any
other impurity, when the whole of the water was flashed into steam,
must have caused a deposit on the top of the amalgam chamber at each
operation. Fresh water, therefore, was needed; the problem arose how
to get it; and that problem was solved, not by the use of surface
condensation, but by the employment of reinjection, that is to say,
the water delivered from the hot well was passed into pipes external
to the vessel; after traversing them, it came back into the injection
tank sufficiently cooled to be used again. The boilers were worked by
coke fires, urged by a fan blast in their ashpits, but I am not aware
that this mode of firing was a needful part of the system.