ON THE SOLIDIFICATION OF CARBONIC ACID. 311 
pressure, at which the mercury reaches the initial point on 
the 2d, and the 2d, suhsequently, exhibits the multiplicators 
of that initial quantity. Thus, if when the mercury is at five 
atmospheres in M, it is at the unit mark in R, the value of 
that unit will be five, and the numbers representative of the 
pressure on R, must be multiplied by five; or R is equal in 
effect to a tube of five times its length. By these means very 
short tubes may be used to determine very high pressures. 
Inequalities in temperature, irregularities in the cement, and 
other causes, may vary the capacity of the socket T, W, but, 
as M always signifies the unit for R, in each case, no error 
can arise from these causes. There must, of course, be a 
correction for the weight of the mercurial column in R, which 
is to be added to the product. Care must be taken to keep 
the temperature of the vessel which holds the liquid below 
that of the gauge and tubes, otherwise the liquid will be 
formed by condensation in the latter. This actually happened 
in the attempt to ascertain the pressure at 86°, when the na- 
tural temperature was 75°. Bubbles of gas were seen ascend- 
ing through a liquid in M, up to its surface, at a few inches 
below the mercurial cylinder. This, as far as relates to the 
tubes may be avoided by prolonging the socket of M, down 
into the mercury of the cup, so as to include a cylinder of 
common air between two cylinders of mercury, and prevent 
any carbonic gas from entering either the socket, or the glass 
tube. A correction for the weight of this column, must, in 
such case, be made. 
When a glass tube, hermetically sealed at one end, and 
cemented into a brass socket and screw at the other, is attached 
to a charged receiver and cooled by snow or pounded ice, liquid 
carbonic acid may be collected in it. It is perfectly colorless 
and transparent, and the specific gravity bulbs, previously 
introduced, are seen to ascend or descend, as the temperature 
is altered. When the tube, so charged, is opened, the liquid 
becomes violently agitated, escapes rapidly, grows colder and 
colder, and finally the remainder is converted into a solid, 
