12 _ Experiments on the 
end, bend up three or four inches of the sealed 
end in the form of a syphon, introduce a drop 
or two of water into the tube, and upon that, 
a few inches ef mercury; bring the mercury 
close up to the sealed end of the tube, so as to 
exclude all the air; and after letting the tube 
rest a little, a small portion of the water will 
ascend to the top of the mercury at the sealed 
end; let the mercury in the open leg be a few 
inches above the level of the closed end. If this 
tube is put into boiling water, and continued 
there ever so long, the small drop of water 
above the mercury will never expand into 
steam, because it has not only te act against 
the weight of the atmosphere, but also the co- 
lumn of mercury ; and the temperature of com- 
mon boiling water is notsufficient to constitute 
steam of an adequate force for that purpose ; 
but if the tube is put into heated mercury, 
and kept there till the temperature rises to 
the proper point for overcoming the pressure, 
(for which see Mr. Dalton’s table) the water 
will then be converted inte steam, and occupy 
a certain portion ef the tube, lifting up the 
column of mercury. If, before the tempera- 
ture is further advanced, more mercury 1s 
poured into the tube, so as to increase the 
pressure of the column a few inches, the steam 
will be immediately condensed into water 
