PREPARATION OF PERCHLORIC ACID. 
315 
quantity of the perchlorates of silver and baryta. It is next 
to be placed in a tubulated retort, and distilled by a gentle 
heat with the same apparatus as that used in the previous ope- 
ration, and with the same precautions as before. As the 
liquor which first distils over is merely water, it should be 
received into a capsule, and the receiver should not be adapted 
until it has been ascertained, by means of test-paper, that the 
acid is coming over. In general, the more slowly the opera- 
tion is conducted, the less water will be retained in the re- 
tort, and the greater the density of the acid. It is well to 
put a few pieces of ice into the water used for cooling the re- 
ceiver. The distillation may be carried on almost to dryness, 
always taking care to avoid the decomposition of the perchlo- 
rates of silver and baryta, which should remain as the residue. 
The perchloric acid thus obtained is perfectly pure, colorless, 
and transparent, its density varies from 60° to 65°, it is olea- 
ginous, like sulphuric acid. From 500 parts of pure per- 
chlorate of potash, I have obtained 150 parts of concentrated 
acid. 
In a future communication, I will give the process for ob- 
taining the pure perchloric acid in crystals. 
Journal de Pharmacie. 
VOL. VIII. — NO. IV. 
40 
