Collect the
filtrate in the flask labelled "arsenic." Boil the precipitate with
dilute sulphuric acid, filter, and titrate the filtrate with the
permanganate of potassium solution after boiling off the sulphuretted
hydrogen. Report the result as iron. The sulphuric acid will not effect
complete solution, a light black residue will remain, chiefly sulphur;
this must be rinsed into the filtrate from the acetate separation. It
contains cobalt.
~Cobalt.~--The filtrate from the acetate separation will have a pink
colour. Render it ammoniacal and pass sulphuretted hydrogen. Collect
the precipitate on a filter, dry, and ignite. Dissolve in hydrochloric
acid, and evaporate nearly to dryness with an excess of nitric acid.
Dilute with 10 or 20 c.c. of water and add potash solution in slight
excess. Add acetic acid until the solution is acid and the precipitate
is quite dissolved. Add 20 or 30 c.c. of a strong solution of potassium
nitrite, and determine the cobalt, as described on pp. 254, 256. Boil
the filtrate from the cobalt, precipitate with hydrochloric acid, render
ammoniacal, and test for zinc, nickel, and manganese.
_The remainder of the tin_ will be contained in the flask labelled
"arsenic." Acidify with hydrochloric acid and filter. Rinse into a
beaker, and evaporate to a small bulk with 10 c.
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