The Students' Guide in Quantitative Analysis - Free Ebooks Library

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(iLrANXri-ATIVE ANALYSI.-,,
When one part of silver is thrown down as AgCJ [^
1,000,000 parts of water, a slight bluish mllkiness maystiU
be seen.
This cloudiness disappears on adding an excess
of HO.
Barium sulphate requires more than 400,000 parts of ''
water for solution. The solubility is not perceptibly
increased by the preseiiee of NaCl, KCIO, or Ba(NO,)„
but HCl produces a sensible increase. (Cf. Storcr's Diction.
ary of Solubilities.)
Barium sulphate thrown down in a solution containing
ferric salts is often contaminated with iron. This becomes
evident by the rcddisli color of the precipitate after ig-
nition. The precipitate may be purified by washing with
ammoniuni acetate, or hy solution in cone. HjSO^, and re-
precipitation by pouring into water. BaSO^ dissolves In
cone. H.SO^ in the ratio of 5.7 parts to lOO, and in Nord-
hausen sulphuric acid as 15.9 to roo.
Analysis No. 2.— Magnesic Sulphate.
MgS0.H-7H,0.
A, — Determiuation of Sulphuric Acid.
See Fres., § 132, I, i. Dissolve i to 1.5 grm. of sub-
stance in warm water, acidulate with HCl, dilute to about
2,50 c.c. ; boil hard ; add Bad, carefully, avoiding a large
excess; boil a few minutes; let the precipitate of BaSO,
settle ; wash
by decantation and on the filter, aiid continue
as in Analysis I, B,
B.— Determination of Magnesium.
. "^•^' § 104, 2. — Dissolve abont 1.2 grm. of substance
>n 150 ec. cold water, in a beaker; add 30 c.c. i\H,Cl,