192 
Steam Engine^ 
ed into vapour : or I put into the said case or cases mer« 
cury or mixtures^ of metals, as of tin, bismuth, and lead, 
capable of being kept in a state of fusion in a lower tem-^ 
perature than that intended to be employed in working 
the steam-engine ; and I so form the surrounding case or 
cases as to make it or them admit the aforesaid oil, or other 
substance employed, to come into contact not only with 
the sides of the steam vessel or vessels, or working cylin- 
der or cylinders, but also with the bottom and top of the 
same, so that the whole may be as much as possible main- 
tained at one uniform temperature ; and this temperature I 
keep up by a fire immediately under or round the case or 
cases that contains the aforesaid oil or other substance, or 
by connecting the said case or cases with a separate vessel 
or vessels kept at a proper temperature, filled with the oil 
or other substance made use of as aforesaid. In some 
circumstances, or whenever the same may be convenient 
or desirable, I employ the fluid metals, or mixtures of me- 
tals, and oil or other of the substances before enumerated, 
at one and the same time in the same engine : that is to 
say, in the part of the case or vessel exposed to the great- 
est action of the fire, I sometimes have the aforesaid me- 
tals or mixtures of metals, and in the parts less exposed 
to the action of the fire, I put oil, or other substances ca- 
pable of bearing the requisite heat without being convert- 
ed into vapour. 
“ By this arrangement, and method of applying the sur- 
rounding heat, I not only obviate the necessity of employ- 
ing steam of a great expansive force round the steam ves- 
sel or vessels, or the working cylinder or cylinders, as al 
ready mentioned, to maintain them at the temperature re- 
quired, but I am enabled to obtain from steam of a com 
paratively low temperature, or even from water itself ad- 
* Chancellor Livingston suggested this idea manv years ago ta 
Dr. Priestley. T. C. 
