176 METAI^-AMMONIA COMPOUNDS.To purify the first product, dissolve it in as little cold water as
possible (about 5 g. of the chloride dissolves in 100 c.c. of water),
filter the solution from any residual chloropentamminecobaltic
chloride, and precipitate the yellow filtrate (keeping the liquid
cold) by the gradual addition of half its volume of concentrated
hydrochloric acid. Yield, 8 to 10 grams.
- The following method may be used to prepare large amounts
of luteocobalt chloride: Prepare as concentrated a solution as
possible of 100 g. crystallized cobalt chloride and 30 g. of ammonium
chloride and add 20% ammonia until the precipitate first formed
has redissolved. Prepare an ammoniacal silver chloride solution
by precipitating silver chloride with NH 4 C1 from 75 g. AgNO 3 and
dissolving the precipitate in 20% ammonia. Mix the latter solu-
tion with the cobalt salt solution and leave the whole for 24 hours
at 40° or two days at room temperature. Collect the precipitate,
which is a mixture of metallic silver and luteocobalt chloride, on a
filter and extract from it the luteo salt with water at 25°. Heat
the extract on the water bath to 80° and add concentrated HC1
until a permanent turbidity just appears; then cool the mixture
by shaking it under the water tap. The desired preparation
thereby crystallizes out perfectly pure. The silver residues are
easily worked up to serve for further quantities of this preparation.
By cautiously acidifying the ammoniacal filtrate from abovewith repeated small portions of concentrated HC1 (avoid much
heating) additional luteo salt may be obtained contaminated with
silver chloride and purpureocobalt chloride. This may be purified
as in la. Total yield, about 80 grams. As by-product about 15
grams of purpureocobalt chloride.
Reactions. A cold, saturated, aqueous solution of the luteo-chloride when treated with ammonium oxalate yields the very
difficultly-soluble oxalate which consists of small, light-brownish-
yellow, irregular crystals. With mercuric chloride a voluminous,
light-pink double salt, [Co(NH 3 ) 6 ]Cls-3HgCl2-H 2 O, is at once thrown
down. Potassium chromate immediately precipitates brownish-
yellow clusters of needles. Potassium dichromate causes the im-
mediate formation of a precipitate which under the microscope is
seen to be crystalline.- Luteocobalt Nitrate by the Iodine Method. Dissolve 24 g. of
cobalt carbonate by warming it with a barely sufficient amount of