418 KCENE ON THE NATURE OF 4QUA REGIA, 
expelled. This water was poured into a flask full of carbonic 
acid*. Acid was now added to the water, and as soon as the 
vessel was filled with it, it was closed hermetically. After the 
cooling of the acid, a couple of drops of hydrochloric acid were 
added, the vessel was then closed and shaken, on opening the 
flask half an hour afterwards a distinct odour of chlorine was 
evolved. 
In this experiment it is requisite,—1, to add the acid to the 
water, that nitric acid may be formed in the first moment of the 
addition ; 2, to arrange it in such a manner that the flask filled 
with the acid mixture contain nearly 6 parts of acid to 1 of 
water, in order that too much water may not be present, and so 
the action of the hydrochloric acid on the nitric acid formed in 
the first moment be not prevented (7.). 
13. Sulphuric acid which had been employed in the concen- 
tration of commercial nitric acid, was heated until its boiling- 
point remained constant. The acid, treated as above with water 
and hydrochloric acid, exhibited the same phzenomena, but no 
chlorine was ever formed with hydrochloric acid alone. 
14. 10 grammes of red nitric acid were added to 150 grammes 
of the concentrated sulphuric acid of the experiment (13.). It 
lost on solution its intense red colour; but on heating the acid 
mixture in a retort with a drawn-out neck bent at right angles, 
the red vapours again made their appearance. An effervescence 
occurred between 170° and 180°C., which arose chiefly from a 
disengagement of oxygen. At 190° this evolution of gas was so 
considerable, that the liquid appeared to boil violently; but 
from this temperature the formation of oxygen decreased per- 
ceptibly, and at 250° no more was disengaged. At the same 
time with the oxygen red nitric acid distilled over, amounting to 
about one-third of what had been added to the sulphuric acid. 
When the temperature of the acid had reached 326°, the 
neck of the retort was introduced into a vessel in which carbonic 
acid was constantly evolved, and the flame of the spirit-lamp 
gradually diminished. The acid, which on boiling possessed an 
intense yellow colour, became perfectly colourless during the 
cooling. 
15. When it had reached the ordinary temperature, the acid 
formed no chlorine with hydrochloric acid; treated previously 
* Since the non-existence of the sulphate of nitric oxide had not then been 
shown, this precaution was necessary. 
