The Students' Guide in Quantitative Analysis - Free Ebooks Library

ANALYSIS OP DOLOMITK. $t
Note 2.— If it is clesimble to determine the SiOj, in the
silicates prcsctU, " Ri'sid/w a" must be treated as follows :
Dry and ignite (with filter), mix in a platinum crucible with
about six parts of Na.CO, (anhydrous), and fuse at a red
heat.
Coo!, remove the fused mass with boiling water, add
an excess of HCl. evaporate to dryness on a water-bath,
heat in an air-bath until the HCl is completely expelled ;
again moisten with HCl, dissolve in water, and filter from
the residue. The residue which is now pure hydrated SiO„
is dried, ignited, and weighed. The filtrate must be added
to " Filtmtc a." Examine Fres., § 140, H, A, a, and § 93, 9-
^^^^, 3.— Heat the filtrate from " Residue a," add NH^Cl,
and NH.HO in slight excess. (The NH.Cl may be omit-
ted if the " Filtrate a " is very acid.) Heat until excess of
NH4HO is expelled, filter quickly, and wash hot. SeeFres.,
^113, i,a,a»d^ 105, I, a.
Note 4.—*' Precipitate b " is partly washed, and then, while
TTioist, dissolved in a little warm dilute HCl on the filter, the
solution is reprecipitated by NH^HO and the precipitate
brought on the same filter, washed thoroughly, dried, and
ignited. Weigh as Fe^Oj-fAUO^. The second filtrate is
added to *' Filtrate d."
Note 5.— Concentrate " Filtrate fi" add some NH^CI un-
less present already, add (NHJ, 0,0, in considerable excess,
and some NH.HO, Let stand 12 hours in a warm
place. Wash partially and filter. Se^ Fres.,% IS4> ^t'
also § ro3, 2, d, a,
AWt' 6.—Dissolve the partially washed " Prm/>ttate c"
in HCl, reprecipitate with NH^HO and a little (NH,)AO,.
Filter and wash hot, add filtrate and washings to " Filtrate
c." Dry precipitate on funnel, transfer to crucible, burn fil-
ter, add ashes, add a few drops of cone. H,SO^ to contents of