88 Steam Engine. 
and he immediately concluded, that, to obtain any consi- 
derable degree of exhaustion, the cylinder and its con- 
tents must be cooled down to 100 degrees at least ; in 
which case, the reproduction of steam in the same cylin- 
der must be accompanied with a great expense of heat, 
and consequently of fuel. He next endeavoured to as- 
certain the temperature at which water boils when placed 
under various pressures ; and, not having any apparatus 
at hand by which he could make his experiments under 
pressures less than that of the atmosphere, he began with 
trying the temperature of water boiling under greater pres- 
sures ; and by laying down a curve, of which the abscissce 
represented the temperatures, and the ordinates the pres- 
sures, he found the law by w^hich the two are connected, 
whether the pressure be increased or diminished. 
Observing, also, that there was a great error in Desa- 
guliers’ calculation of the bulk of water when converted 
into steam, and that the experiment on which he founded 
his conclusion was in itself fallacious, he thought it es- 
sential to determine this point with more accuracy. By 
a very simple experiment with a Florence flask, which 
our limits will not allow us to detail, he ascertained, that 
water, when converted into steam under the ordinary pres- 
sure of the atmosphere, occupies about eighteen hundred 
times its original space. 
These points being determined, he constructed a boiler 
in such a manner, as to show by inspection, with tolera- 
ble accuracy, the quantity of water evaporated in any 
given time ; and he also ascertained by experiment the 
quantity of coals necessary to evaporate a given quantity 
of water. if. 
He now applied his boiler to the working model above 
mentioned ; when it appeared^ that the quantity of steam 
expended at every stroke, exceeded many times what 
was sufficient to fill the cylinder ; and deducing from 
