ON THE LIQUEFACTION OF GASES. 21 
state without being dispersed in the form of snow, consti- 
tutes a very beautiful substance, transparent like crystal, so 
that for some time I doubted whether the tube which con- 
tained it was empty or full ; and I was even obliged, in 
order to ascertain the presence of the solid body, to melt a 
portion of it. Solid carbonic acid exerts a pressure of 6 
atmospheres, which proves how readily liquid carbonic acid 
ought to become solid when allowed to escape into the free 
air. 
Oxide of chlorine is a beautiful, orange-red, very friable, 
crystalline substance. It exhibits no trace of explosive 
power. 
Protoxide of nitrogen is one of the gases which I had 
formerly condensed. I have seen in the journals that M. 
Natterer has repeated my experiments with a compression- 
pump, and that he has obtained the liquid in the open air. 
I have likewise condensed it to a liquid by means of my 
pump, but I have moreover solidified it by means of the 
cold bath. It then forms a beautiful transparent or color- 
less crystalline body, but in this state the pressure of its va- 
por does not amount to that of 1 atmosphere ; and this re- 
sult is confirmed by another experiment, in which, having 
opened a vessel containing this liquid, a portion evaporated, 
cooled the remainder, but did not solidify it. The cold pro- 
duced by this evaporation is very intense, which was proved 
by placing the tube and its contents in a bath of solid car- 
bonic acid and aether in the air. This bath, which instantly 
freezes mercury, behaved like a vessel filled with hot liquor, 
and immediately caused the protoxide of nitrogen to boil 
violently. It is therefore my intention to employ the liquid 
protoxide of nitrogen for some new experiments on hydro- 
gen, oxygen and nitrogen ; for on placing a bath of this 
liquid protoxide in the receiver of an air-pump, and ex- 
pelling the air and the gas, we are able to place the bath 
of the protoxide relatively to that of the carbonic acid in 
vacuo, in the same relation that the two baths observe in 
the air. 
