314 
PREPARATION OF PERCHLORIC ACID. 
justed, the use of lutes may be avoided, but if found neces- 
sary, a little asbestus will answer the purpose. On carefully 
applying heat, the whole of the perchlorate will soon dissolve, 
and some management will be necessary, in regulating the 
heat, to prevent a quantity of sulphuric acid from passing over 
in the distillation. The best way to regulate the operation is 
to avoid ebullition, by always keeping the heat a little below 
that point. In this way very little sulphuric acid will pass 
over, and this may be known, for perchloric acid rises in va- 
por at 316° Fahr., a temperature much below that at which 
sulphuric acid distils. It may be ascertained that the opera- 
tion is terminated by the residue in the retort being quite 
transparent and yet colorless, or still better, by the drops 
coming over slowly, although the temperature is nearly suffi- 
cient to carry over the sulphuric acid. The quantity result- 
ing from the distillation will vary in each operation, according 
to the manner in which the process has been conducted; this 
difference depending upon the greater or less quantity of sul- 
phuric acid, which is carried over in the distillation. As an 
average, the above process, conducted with care, yielded 300 
parts of impure acid of about 45° density from the quantity 
specified of perchlorate. Should the operation be conducted 
too fast, the density of the impure acid will be nearly that of 
sulphuric acid, and the quantity equal to the perchlorate em- 
ployed. 
It is very easy to render this acid pure, by removing the 
sulphuric acid and the small quantity of chlorine which it 
contains. For this purpose, it is first to be shaken with a 
slight excess of a saturated solution of sulphate of silver; the 
chlorine will be precipitated with the silver; this precipitate 
is to be separated with a filter, and the acid put into a large 
capsule; hydrated carbonate of baryta, prepared artificially 
and well washed, is now to be added until the whole of the 
sulphuric acid has been thrown down, and a small quantity of 
perchlorate of baryta formed; the precipitate is again to be 
separated by a filter. The liquor will now contain nothing 
but perchloric acid, combined intentionally, with a small 
