Required. in the Distillate.
5 minutes 12.0 c.c. 0.0450 gram
5 " 0.17 " 0.0005 "
5 " 0.0 "
5 " 0.0 "
To dryness 0.0 "
The volume of each distillate was about 5 c.c.
In this operation the metals are converted into chlorides by the action
of ferric chloride, which gives up a part of its chlorine, and becomes
reduced to the ferrous salt. The calcium chloride does not enter into
the chemical reaction, but raises the temperature at which the solution
boils, and is essential for the completion of the distillation.[105] Two
experiments with material containing 3.48 per cent. of arsenic gave--(1)
with ferric chloride alone, 2.74 per cent.; and (2) with the addition of
calcium chloride, 3.48 per cent.
It is always necessary to make a blank determination with 1 gram of
electrotype copper, to find out the amount of arsenic in the ferric
chloride mixture.[106] Unfortunately, a correction is always required.
This amounts to about 0.15 per cent. of arsenic on each assay, even when
the mixture has been purified; and this constitutes the weakness of the
method, since, in some cases, the correction is as much as, or even
greater than, the percentage to be determined.
The acid distillate containing the arsenious chloride may be left for an
hour or so without much fear of oxidation; but it is safer to neutralise
and then to add the bicarbonate of soda, as the following experiments
show.
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