LIQUID CARBONIC ACID. 
61 
from a liquid to a gaseous state. When a jet of liquid car- 
bonic acid is directed on the bulb of a spirit thermometer, the 
alcohol rapidly sinks to — 90° C, but the frigorific effects do 
not correspond to this great depression of temperature; this is 
owing to the almost total absence of conductibility and the 
slight capacity for caloric possessed by the gas; hence, the in- 
tensity, although enormous, is limited to the point of contact; 
congelation of mercury can only be produced in very minute 
quantities, and if the finger be exposed to a jet of the liquid, 
a highly painful sensation of burning is produced; but the in- 
jury is almost always confined to the epidermis. 
When ether is mixed with liquid carbonic acid, the ether 
becomes volatilized. The effects produced by a blowpipe fed 
with ether rendered gaseous by means of carbonic acid are re- 
markable; a few seconds suffice to congeal fifty grammes of 
mercury. If the finger be exposed to the jet, the sensation is 
intolerable. 
Carbonic acid, gaseous at common temperatures and under 
the ordinary pressure, and liquid under a pressure of thirty- 
six atmospheres, also becomes solid about — 100° C, and re- 
mains in this state for a few minutes in the open air, and un- 
der the usual atmospheric pressure, whilst at ordinary tempe- 
ratures its expansive force is so great that it produces an 
explosion as powerful as the same weight of gunpowder. 
This solidification can also be produced by directing a jet 
of carbonic acid into a small vial; this becomes almost in- 
stantly filled with a white pulverulent flocculent substance, 
which adheres very firmly to the glass, and cannot be remov- 
ed without breaking the bottle; the promptness with which 
this product forms in cavities impervious to air or the vapour 
of water, is one of its most remarkable characteristics. 
In assigning — 100° C. as the point of solidification of liquid 
carbonic acid, the author is sustained by facts in the experi- 
ment made before the committee of the Academy; a spirit 
thermometer sank to — 87° C; by adding to these 87° the six 
degrees which the alcohol would have sunk, if the whole tube 
had been subjected to the frigorific action, we have 93°, a 
