Laboratory Methods of Inorganic Chemistry, 2nd English Ed. 1928

AMMONIUM PLUMBIC CHLORIDE. 143

piece of linen laid in a large Biichner funnel, and return the fil-

trate to the beaker.

When the reaction is complete remove the silicic acid, as above,

with a linen filter, and estimate the yield by analyzing a sample of

the filtrate. Either titrate hot with 0.1-normal sodium hydroxide,

using phenolphthalein as indicator, whereby the reaction is

H 2 SiF 6 + 6 NaOH = 6 NaF + H 4 Si0 4 + 2 H 2 O,

or else add to the solution an excess of neutral calcium chloride

and titrate the hydrochloric acid set free, using methyl-orange as

indicator:

H 2 SiF 6 + 3 CaCl 2 + 4 H 2 O = 3 CaF 2 + 6 HC1 + H 4 Si0 4.

Add some potassium chloride solution to another sample of the

product; the difficultly soluble potassium salt separates, and,

although the precipitate is barely visible at first, the liquid is

eventually left in a jelly-like condition.

104. Potassium Titanium Fluoride, K 2 [TiF 6 ].
     Allow 19 g. of titanium tetrachloride (No. 52) to flow very
     slowly from a dropping funnel into 20 c.c. of ice-cold water in a
     platinum dish. (Hood.) The dish must meanwhile be kept sur-
     rounded with ice. Add 30 g. of pure, 40 to 50% hydrofluoric acid
     to the mixture, and then a warm concentrated solution of 15 g.
     potassium chloride; the contents of the dish thereupon harden
     to a crystalline paste. Evaporate to complete dryness on the
     water bath, to remove the excess of hydrofluoric acid, and recrystal-
     lize the difficultly soluble residue from water. Yield, about 20 g.


105. Ammonium Plumbic Chloride, (NH 4 ) 2 [PbCl 6 ]. Lead
     Tetrachloride, PbCl 4.
     Triturate 10 g. of lead chloride, PbCl 2 , with 20 c.c. of concentrated
     hydrochloric acid; after allowing the suspension to settle some-
     what, decant off the solution together with the fine, suspended
     solid; repeat the above treatment with the residue until all of

the lead chloride is in solution or in a state of finest suspension in
200 c.c. of hydrochloric acid.
Place mixtures prepared in this manner in each of two 250 to
300 c.c. gas-wash-bottles, and, while keeping the temperature at
10° to 15° and shaking occasionally, pass a slow current of chlorine