7 :: 0.6 : 0.3222, or 32.2 per cent.
With the test-tube method of dry assaying, this same sample gave results
varying from 33 to 35 per cent. of white arsenic, which (judging from
its appearance) was impure.
URANIC ACETATE PROCESS.
This may be looked upon as an alternative to the gravimetric method. It
is applicable in all cases where the arsenic exists in solution as
arsenic acid or as arsenate of soda. The process may be considered in
two parts: (1) the preparation of the solution, and (2) the titration.
~Preparation of the Solution.~--If the arsenic has been separated as
sulphide, it is sufficient to attack it with 10 or 15 c.c. of nitric
acid, and to heat gently till dissolved, avoiding too high a temperature
at first. Afterwards continue the heat till the separated sulphur runs
into globules, and the bulk of the acid has been reduced to 3 or 4 c.c.
Dilute with 20 or 30 c.c. of water; put in a piece of litmus paper; and
add dilute ammonia until just alkaline. Then add 5 c.c. of the sodium
acetate and acetic acid solution (which should make the solution
distinctly acid); dilute to 150 c.c., and heat to boiling. The solution
is ready for titrating.
When the arsenic exists in a nitric acid solution mixed with much
copper, it is separated in the way described under _Examination of
Commercial Copper_ (Arsenic and Phosphorus), pages 208, 209.
Pages:
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715