194 
Steam Engine, 
is called a single engine, a less considerable altitude of 
metal is required, because the steam always acts on the 
upper side of the piston. For single engines, oil, or wax, 
or fat of animals, or similar substances, in sufficient quan- 
tity, will answer the purpose, if another improvement, 
which constitutes part of my said invention, be applied to 
the engine, namely, to take care tliat either in the double 
or single engine so to be worked, the outlet that conveys 
the steam to the condenser shall be so posited, and of such 
a size, that the steam may pass without forcing before it 
or carrying with it any of the metal or other substance 
employed, that may have passed by the piston ; taking 
care at the same time to provide another exit for the metal 
or otlier substance collected at the bottom of the steam 
vessel or working cylinder to conveys the same into a re- 
servoir kept at a proper heat, whence it is to be convey^- 
ed to the upper side of the piston by a small pump work- 
ed by the engine or by any other contrivance. In order 
that the fluid metal or metals used with the piston may 
not be oxidated, I always keep some oil or other fluid 
substance on its surface, to prevent its coming in contact 
With the atmosphere and to prevent the necessity of em - 
ploying a large quantity of fluid metal, I generally make 
my piston of the depth of the column required, but of a 
diameter a little less than the steam vessel or working cy- 
linder, excepting where the packing or other fitting is ne- 
cessary to be applied ; so that, in fact, the column of fluid 
metal forms only a thin body round the piston. In some 
cases I make a hollow metallic pistoiv, and apply an altitude 
fluid of metal in the inside of the same, to press its outside 
into contact with the steam vessel or working cylinder, 
“ It may be necessary, however, to state, that in apply- 
ing my improved method of keeping the steam vessels of 
steam engines at any required temperature to the engine 
known by the name of Savary’s, in any of its improved 
