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was constructed, the tube being Aths of an inch in internal 
diameter, and 35 inches high. Into this tube mercury and 
sulphuric acid were introduced, as in the first tube. But 
on trying to get rid of the small bubbles of air, it was found 
impossible to do so as small bubbles were continually gen- 
erated. Hence it appeared that the three weeks during 
which the mercury and sulphuric acid in the first tube had 
remained in contact hsd had an important influence on the 
result. Failing in this attempt, it occurred to me to try if 
water would answer the purpose as well as sulphuric acid. 
Having in my possession an old vacuum gauge, with a 
column 3 inches long, which had originally been wetted 
with sulphuric acid, but into which a considerable quantity 
of water had accidently been introduced, I carefully allowed 
all the air to escape, and then applied a mercurial air pump 
to the open end of the gauge, and exhausted as far as the 
pump would draw. The mercury did not descend. As I 
could apply no further tension I shook the gauge up and 
down, but still the mercury remained unmoved. I then 
tapped the gauge smartly on the side, the mercury then fell 
3 inches, until it was level. Having succeeded so far, I 
extracted the mercury and sulphuric acid from the 35 inch 
gauge and introduced some water without washing the tube, 
and having boiled the water in the tube, again introduced 
the mercury. 
Having extracted all the air, I found no difficulty in 
making the gauge to stand up to the 35 inches without any 
immediate tendency to fall. On applying the air pump to 
the open end the mercury several times remained up until 
the exhaustion had proceeded so far that when it fell it fell 
from 22 to 28 inches, and when the rupture took place it was 
accompanied with a loud click. I could not on that occa- 
sion get the mercury to withstand complete exhaustion, but 
after leaving the gauge with the mercury suspended for 24 
hours at 35 inches, I was able to exhaust the open end of 
