61 
Steam 3ngine. 
aot true, either with regard to spirit of wine or any other 
liquid. Experiments made upon six dilTereiit liquids a» 
gree in establishing this as a general law ; namely, that 
the variation of the force of vapour from all liquids is the 
same for the same variation of temperature^ reckoning 
from vapour of any given force : thus assuming a force 
equal to thirty inches of mercury as the standard, it being 
ihe force of vapour from any liquid boiling in the open air, 
we find aqueous vapour loses half its force by a diminution 
of 30° of temperature ; so does the vapour of any other 
liquid lose half its force by diminishing its temperature 30^ 
below that in which it boils ; and the like tor any other 
increment or decrement of heat. This being the case, it 
becomes unnecessary to give distinct tables of the force of 
vapour from different liquids, as one and the same table 
is sufficient for all. But it will be proper to relate the ex- 
periments on which this conclusion rests. 
Experiment on Sulphuric Ether, 
The ether I used, boiled in the open air at 102 degrees. 
I filled a barometer tube with mercury, moistened by agi« 
tation in ether. After a few minutes a portion of ether 
rose to the top of the mercurial column, and the height of 
the column became stationary. When the whole had ac» 
quired the temperature of the air in the room, 62 the 
mercury stood at 17.00 inches, the barometer at the same 
time being 29,75. Hence the force of vapour from ether 
at 62^ is equal to 12.75 inches of mercury, which, accords 
with the force of aqueous vapour at 172^, temperatures 
which are 40^ from the respective boiling points of the 
liquids. By subsequent observations I found the forces 
of the vapour from ether in all the different temperatures 
from 33® to 102® exactly corresponded with the forces of 
aqueous vapour of the like range^ namely^ from 142® to 
