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PURIFICATION OP NITRIC ACID. 
off, in the first third of the acid, more than half the water it 
originally contained. 
There is then to be added to the residue remaining in the 
retort, its volume of concentrated sulphuric acid; a very 
dense acid will be obtained by the first distillation, and this 
may be brought to the highest state of concentration by re- 
peated distillations. During the distillation from sulphuric 
acid, the nitric acid carries over an appreciable quantity 
with it; on the other hand, the sulphuric acid in the retort 
retains a portion of the nitric acid, although the temperature 
be raised to 680° Fahr. The combination of sulphuric and 
nitric acids described by Kulmann, is no doubt formed 
here, and which, as is seen, is decomposed with great diffi- 
culty. When the decomposition is effected, pure oxygen 
is disengaged, and there remains in the vessel a combina- 
tion of sulphuric acid and deutoxide of azote. 
When the nitric acid has been separated, by a second dis- 
tillation, from the sulphuric acid which it had carried over, 
it always contains a large quantity of nitrous acid. When 
in this state, it should be put into the vessel in which it is 
intended to be kept, and the temperature being raised to the 
boiling point, a current of dry carbonic acid should be 
passed through it. It should then be allowed to cool, still 
continuing the current of gas. If the density of the acid 
does not exceed 1.50, one operation of this kind will be 
sufficient to render it colorless; but with more concentrated 
acid, it is necessary to raise the temperature to ebullition, 
two or even three times. 
In those cases where, after the first purification, the acid 
is nearly colorless, the purification may be completed by 
adding some fragments of white nitrate of urea. 
The most concentrated acid that M. Millon was able to 
obtain by the application of heat and a current of carbonic 
acid gas, was perfectly colorless, very fuming, and not ren- 
dered turbid by sulphuretted hydrogen, when diluted with 
two or three volumes of water. According to the analyses 
