ON ANHYDROUS NITRIC ACID. 
269 
and its displacement is produced by a slow and constant 
flow of concentrated sulphuric acid ; the chlorine is passed 
over chloride of lime, and then over pumice-stone moistened 
with sulphuric acid. At the ordinary temperature nothing 
appears to be produced ; the nitrate of silver must be heated 
to 203°, and the temperature then immediately lowered to 
136° or 154°, beyond which it should not go. At first 
some hyponitric acid is developed, recognizable from its 
color and its ready condensation ; then, as soon as the tem- 
perature has reached the lowest point, the production of 
crystals commences, and they soon obstruct the recipient 
cooled to — 6° F. They are always deposited on the por- 
tion of the receiver which is not immersed in the freezing 
mixture ; and M. Deville has found that ice alone sufficed 
to determine their production. The gases are colored, and 
the spherical reservoir of the cooled tube contains a small 
quantity of liquid, which must be removed from the appa- 
ratus before transferring the nitric acid into another vessel. 
This last operation is easily effected by substituting a cur- 
rent of carbonic acid for the one of chlorine. The con- 
denser is no longer cooled, and the bulb destined to receive 
the crystals is immersed in a refrigerating mixture, which 
is connected with the apparatus by means of a caoutchouc 
tube lined with asbestos. The chlorine should pass very 
slowly, between 3 and 4 litres in twenty-four hours. How- 
ever, the whole of the gas is not absorbed by the nitrate of 
silver. Some oxygen is given off, apparently very nearly 
equal in volume to the chlorine consumed. An apparatus 
thus arranged goes on day and night without any looking 
after. It is merely necessary to renew the supply of sul- 
phuric acid which displaces the chlorine, the alcohol which 
feeds the lamp, and the freezing mixture,— Co mptes Ren- 
dus, Feb. 17, 1849. 
At a recent meeting of the Academy, (March 5) M. Du- 
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