ON AQUA REGIA AND HYPOSULPHURIC ACID. 205 
rine were expelled ; half of this was then again treated with 
a current of hydrochloric acid, but this time no chlorine was 
produced. A portion of the other half was mixed with one- 
sixth of its volume of water freed from air. This water 
was introduced into a flask filled with carbonic acid.* The 
water was acidulated with the acid, and as soon as the flask 
became filled it was hermetrically closed. On allowing the 
acid to cool, two drops of hydrochloric acid were added, 
the vessel was then closed and shaken. After half an hour 
the vessel was opened, when a distinct odour of chlorine 
was perceived. 
In this experiment, care must be taken, 1st, that the acid 
be added to the water, that, immediately on the addition, 
nitric acid maybe produced; 2d, that about six parts of 
acid to one of water be contained in the flask, to prevent 
an excess of water from counterbalancing the action of the 
hydrochloric acid on the nitric acid, at the moment of its 
formation (7.) 
13. The sulphuric acid previously employed in the con- 
centration of nitric acid was heated until it arrived at a 
constant boiling point. The acid, on being treated as above, 
with water and hydrochloric acid, exhibited the same phe- 
nomena, but by an addition of hydrochloric acid alone 
chlorine was never formed. 
14. To 150 grammes of the concentrated sulphuric acid 
of experiment 13, 10 grammes of red nitric acid were added. 
By this solution, the latter lost its intense red colour ; how- 
ever, on heating the acid mixture in a retort, the neck of 
which was drawn out, and bent into a rectangle, the red 
vapours disappeared. Between 338 and 356° F. an effer- 
vescence took place, which seems chiefly to be derived from 
a disengagement of oxygen. At 374° F. the disengagement 
of gas became so powerful that the liquid seemed to boil ; 
but at higher temperatures the formation of oxygen con- 
*The non-existence of sulphate of oxide of nitrogen not being as- 
certained, it was necessary to take the above precaution. 
