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

TUNGSTEN COMPOUNDS FROM WOLFRAMITE. 229

there vaporizes, and then continue to heat so that 5 to 10 cm. of
the section CD remains constantly filled with red vapors. At
first there is no evidence of chemical change; but after some time
hydrogen chloride can be recognized in the escaping gases, and,
on continuously vaporizing the pentachloride, which repeatedly

condenses and flows back, a copper-red film is deposited, and

gradually a mass of the same or often a darker color is produced.
Carry the heating gradually towards D until finally all the pen-
tachloride is converted to the trichloride; two to three hours are

required for this. Too strong heating is to be avoided, for the

lower the temperature at which the transformation takes place

the better the preparation. Finally, replace the hydrogen by car-
bon dioxide and distil the remainder of the pentachloride from

the 8 cm. section so that its vapor passes over the trichloride.

Allow none of the pentachloride to remain with the preparation,

but drive out all the excess at D after removing the escape tube

which leads to the flue. Allow the preparation to cool, cut the

tube into several pieces, and remove the crystals with a glass

rod. Yield, 4 to 6 g. The product is not hygroscopic; it consists

usually of a crystalline mass the color of red phosphorus but
sometimes of feathery crystalline aggregates.

167. Tungsten Compounds from Wolframite.
     The most common tungsten mineral is wolframite, which is essentially a
     mixture of manganous and ferrous tungstates.

(a) Ammonium Tungstate, 5 (NH 4 ) 2 WOt. 7 WO 3 .11 H 2 O.

Boil 200 g. of finely powdered wolframite gently for about

three hours in a 300-c.c. Erlenmeyer flask with 50 c.c. of concen-

trated hydrochloric acid and 10 c.c. of concentrated nitric acid;

replace from time to time the acid as it evaporates. Then dilute

the mass with a large amount of water and decant off the solu-
tion, which contains chiefly ferric and manganous chlorides, from

the grayish-yellow easy-settling residue. Again boil the residue

gently for two hours with the same mixture of acids and repeat

the washing and decantation.

Dilute the decanted liquids to a volume of 1.0 to 1.5 liters,

and if after several hours a yellow precipitate of tungstic acid
separates, collect it on a filter after pouring off most of the liquid,

and add it to the main insoluble residue.