Memoir on Sulphuric Ether. 469 
and its long leg filled th various heights with 
‘mercury, according to the temperature. It 
may be advantageously used from 120 to 
‘140°. For temperatures between 140° and 
212°, I have always used a tube similar to the 
last mentioned, but having its upper extre- 
mity sealed, and containing air of common 
density over the mercurial column, and nearly 
equal in volume to the capacity of the other 
leg. When the ether vapour is formed in 
force, it condenses the said air, and from the 
condensation, the force is inferred by a well 
known law.—Having had some reason to sus- 
pect my former results by this instrument 
were somewhat too high; I have been indu- 
ced to examine the defects to which this in- 
strument is liable. The end of the tube 
must be drawn out to a point before sealing, 
and suffered to cool to the temperature of the 
air; after this the end must be closed by the 
point of a flame, otherwise the air in the 
tube may be rarefied by the heat, in which 
case the force of the steam will be overrated. 
Another cause of similar error, is the exis- 
tence of ether vapour in the air at the mo- 
ment of sealing; this will happen if the tube 
is not carefully dried inside after the instru- 
ment is filled with mercury. In this case, 
the air in the tube is rarefied by the steam, 
