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

184 METAL-AMMONIA COMPOUNDS.

nor do they give precipitates with mercuric chloride, with oxalates,

or with chromates.

140. Hexaminlnechroniic Nitrate, Cr(NH 3 ) 6 3 and Chloro-
     pentamminechromic Chloride, [Cr(NH 3 )i,Cl]Cl 2.
     Anhydrous chromic chloride, when in contact with liquid ammonia, takes
     up partly five and partly six molecules of ammonia. The hexammine salt
     dissolves readily when the mixture is treated with cold water, and from the
     filtrate the nitrate can be precipitated by the addition of nitric acid. The
     chloropentammine chloride, on the other hand, does not dissolve in the cold
     water, but can be purified by suitable recrystallization.^1
     Chloropentamminechromic chloride (chloropurpureochromic chloride) fur-
     nishes an excellent illustration of the fact that the characteristic properties of
     these complex compounds are often less influenced by the nature of the metal
     present than by the type of combination. Chloropurpureochromic chloride
     is so similar to chloropurpureocobaltic chloride that it is necessary to decom-
     pose the substances completely in order to prove that the metal is different.

Generate ammonia by heating 500 g. of concentrated ammonia

solution on a Babo funnel, dry the gas by passing it through two

towers filled with lime and through a U-tube containing sodium

hydroxide, then condense it to a liquid in an Erlenmeyer flask

containing 8 g. of finely powdered, anhydrous chromic chloride

(No. 43). In order to exclude carbon dioxide from the condensing

flask, this must be closed with a stopper and provided with an

inlet and an outlet tube. For the cooling agent use a mixture

of carbon-dioxide-snow and ether (temperature about —80°)

placed in a small beaker, which in turn is placed within a larger

beaker so that an inclosed air space between the glass walls shall
act as an insulator.

When the chromic chloride has combined with the liquid

ammonia, forming a reddish-brown mass, stop the operation and

allow the excess of ammonia to evaporate from an open dish.
Triturate the residue with 30 c.c. of ice-cold water, filter and wash

the undissolved salt with a little cold water until the filtrate runs

through of a reddish color. Add concentrated nitric acid to the

filtrate, which precipitates luteo-chromic nitrate. Again filter,
dissolve the salt in a little warm water containing a few drops of

(^1) For a method of preparing chloropurpureochromic chloride without the
use of liquid ammonia, cf. O. Christensen; J. pr. Chem. (2) 33, 54 (1881) and

8. M. Jorgensen, ibid. 30, 105 (1879).