Liquefaction and Solidification of Carbonic Acid. 355 



the latter. This actually happened in the attempt to ascertain 

 the pressure at 86°, when the natural temperature was 75°. 

 Bubbles of gas were seen ascending 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 niade. 



When a glass tube, hermetically sealed at one end, and cemen- 

 ted into a brass socket and screw at the other, is attached to a 

 charged receiver and cooled by snow or pounded ice, liquid car- 

 bonic 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 vio- 

 lently agitated, escapes rapidly, grows colder and colder, and 

 fiinally the remainder is converted into a soHd, more dense than 

 the snow already described, but nearly white, and very porous. 

 If the tube be exposed to a paste of carbonic snow and ether, the 

 liquid is solidified into amass which is not porous but which sinks 

 in the liquid as the latter is formed again by the melting of the solid. 



The analogy between liquid carbonic acid and water, is thus 

 completed for we have liquid, vapor, snow, and ice, exhibited by 

 both. 



By the previous introduction of water, ether, alcohol, metals, 

 oxides, or oils, &.c. into such tubes, and then filling them with 

 liquid carbonic acid, the resulting phenomena may be easily 

 observed. Yf ater being heavier rests below the new liquid, and 

 does not appear to mingle with it even at the surface of contact, 

 for when the latter is let off no bubbles appear in the water, and 

 it is frozen at the top into solid ice. 



When alcohol or ether is introduced, the new liquid falls 

 through it in streams, as water would do, but soon renders it 

 milky by mixture. The removal of the pressure causes a violent 

 effervescence, and immediately the clear, colorless ether, or al- 

 cohol, is seen alone in the tube ; no solid being formed. When 

 alcohol holds shell-lac in solution, the acid causes its precipitation 

 in light whitish flocculi, which are immediately re-dissolved 



