AND ON THE CONSTITUTION OF HYPONITRIC ACID. 419 
with water, as in the experiments (12, 13.), the acid yielded 
chlorine on the addition of some hydrochloric acid. 
Another portion of the acid mixed with alcohol, access of air 
being prevented, formed nitric ether. Copper dissolved in it 
with a violet colour and with disengagement of nitric oxide. 
After having adapted a funnel with a cock into the tubulure of 
a retort containing water, carbonic acid was first conveyed into 
the funnel and then 26 grammes acid. Upon this heat was ap- 
plied, and when the water boiled, the cock was opened. The 
temperature of the water rose considerably by the addition of 
the acid; at the same time red vapours were evolved, which were 
received in water containing carbonate of lime in suspension ; 
it was then heated until the temperature of the acid had attained 
the boiling-point of sulphuric acid. The liquid decanted from 
the carbonate of lime was evaporated to dryness and the residue 
exhausted with alcohol. The alcoholic liquid yielded on desicca- 
tion a residue which left on ignition 0°21 gramme lime. 
Having established these facts, we will now apply them to aqua 
regia and hyponitric acid, to ascertain more precisely the nature 
of these liquids. 
On the Nature of Aqua Regia. 
16. qua reyia is characterized and effective only under 
very special conditions. The circumstances which principally 
prevail at its formation, are the temperature, the degree of con- 
centration of the two acids forming it, and the presence of a 
body capable of combining with the chlorine. 
17. No reaction takes place in a mixture of hydrochloric and 
nitric acid, both concentrated, at a very low temperature; the 
cold liquids mix without acquiring any colour and without eli- 
mination of chlorine, but on being removed from the refrige- 
rating mixture, to a place where the temperature is 0°, it gradually 
becomes coloured and disengages chlorine: 
18. A mixture of 2 volumes of hydrochloric acid of 37°60 
per cent. and 1 volume of red nitric acid begins to form chlorine 
only at —12°C. Nitric acid of 74:5 per cent. of real acid 
begins with the same hydrochloric acid, to become coloured and 
form chlorine near about ~6°C. The presence of a larger 
quantity of water delays the action still more, and when the acids 
are very dilute, the action does not occur even on the applica- 
tion of heat; but if in the latter case a metal is immersed in the 
liquid, the effect is immediately produced and water is formed. 
