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

150 NITRITO ACIDS AND SALTS.

the solution. After standing 2 hours collect the precipitate and

wash it twice with 25 c.c. of alcohol. Yield, 51 to 52 g.

Purify the crude product by recrystallizing it in three portions,

each of which is stirred up with 1.5 times its weight of cold water.

Filter off the small undissolved residues, and precipitate each of

the clear nitrates by injecting from the wash-bottle, as above,

50 c.c. of a mixture of alcohol and a little glacial acetic acid

(70 : 1). Wash the precipitate with alcohol and ether, and dry

it at a temperature not exceeding 80°. Yield, about 40 g.

Potassium Cobaltinitrite. To the combined mother-liquors from

the above, add potassium chloride solution until precipitation is

complete. Collect, wash, and dry the yellow, crystalline precipitate.

The aqueous solution of the readily soluble sodium cobaltinitrite

is a useful reagent in testing for the presence of potassium ions.

115. Potassium Tetranitrito-diammine-cobaltate,
     K[Co(NO 2 ) 4 (NH 3 ) 2 ].
     Dissolve 10 g. of cobaltous carbonate in a barely sufficient
     amount of hydrochloric acid, so that a trace of residue remains
     undissolved and the solution is only faintly acid. Dilute the
     solution to 200 c.c. with water and add 70 g. of ammonium chloride,
     whereupon the color changes from red to violet. Warm the

liquid to 50° and add a solution of 100 g. of potassium nitrite in

100 c.c. of water which is likewise warmed to 50° (use a large

beaker on account of foaming). Maintain the mixture at 50° for
half an hour and then place it in the ice-chest for 24 hours. Dull-
brown crystals and a fine yellow powder separate; the latter may

be removed by rotating the mass two or three times with 100 c.c.

of cold water and each time pouring the liquid and the suspended

matter away from the brown crystals.

Dissolve the crude product in 150 c.c. of boiling water; filter

and cool the filtrate at once, because the salt is decomposed in hot

solution. The main part of the salt crystallizes on cooling; wash

it with a little water and then with alcohol. The addition of
alcohol and a little ether to the mother-liquor causes the remainder

of the salt to precipitate, and this should be recrystallized from a

little water. Yield, 8 g. of brown, lustrous crystals.

A cold saturated aqueous solution gives yellowish-brown prisms

or rhombic leaflets when treated with mercurous nitrate solution.