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PREPARATION OP PERCHLORIC ACID. 
ART. LIII PREPARATION OF PERCHLORIC ACID. 
By M. Ad. Nativelle. 
Perchloric acid, so valuable as a reagent, is seldom met 
with in our laboratories. This arises no doubt from the small 
quantity of the acid which is obtained by using the propor- 
tion of sulphuric acid generally directed in books, rather than 
from any difficulty in the operation, which, in itself, is suffi- 
ciently simple. It is merely necessary, as is known, to in- 
troduce into a glass retort, one part of perchlorate of potash 
with half its weight of sulphuric acid diluted with a third 
part of water, and apply heat to obtain the perchloric acid, 
much diluted it is true, and in very small quantity in propor- 
tion to that of the perchlorate employed. On examining the 
phenomena which take place in this operation, it will be ob- 
served, that the water employed to dilute the sulphuric acid 
first passes over without any acidity, and although at this pe- 
riod of the operation, the contents of the retort are in active 
ebullition, nearly the whole of the perchlorate remains undis- 
solved. It is not until a subsequent period, when the sul- 
phuric acid has regained its original concentration, that a part 
of the perchlorate begins to be decomposed, but as the pro- 
portion of sulphuric acid is much too small for the perchlorate 
of potash used, the distillation proceeds very slowly, and a 
part of the free perchlorate is decomposed by the heat, as it 
would be if alone, into oxygen and chlorate of potash. This 
chlorate, aided by the action of the heat and the surrounding 
acid, is easily decomposed into oxygen and oxide of chlorine, 
and even chlorine. These gases are disengaged during the 
continuance of the operation, and if at the end of the process, 
the residue contained in the retort be examined, a large pro- 
portion of the perchlorate will be found unacted upon. As 
for the product of the distillation, as I have already stated, it 
is but slightly acid, especially if the precaution has not been 
