IRON. 
§§ 9 I2 > 9 X 3*] 
711 
is now made almost neutral by potassic carbonate, and then potassic 
acetate added, and a current of sulphuretted hydrogen passed through 
it. The sulphides of cobalt and nickel, if both are present, will be 
thrown down ; under the same circumstances zinc, if present, would 
also be precipitated. Cobalt is separated from zinc by dissolving the 
mixed sulphides in nitric acid, precipitating the carbonates of zinc and 
cobalt by potassic carbonate, collecting the carbonates, and, after wash¬ 
ing, igniting them gently in a bulb-tube in a current of dry hydrochloric 
acid ; volatile zinc chloride is formed and distils over, leaving cobalt 
chloride. 
§ 912. To estimate cobalt, sulphide of cobalt may be dissolved in 
nitric acid, and then precipitated by pure potash ; the precipitate 
washed, dried, ignited, and weighed; 100 parts of cobaltous oxide 
(Co 3 0 4 ) equals 73*44 of metallic cobalt. Cobalt is separated from nickel 
by a method essentially founded on one proposed by Liebig. The nitric 
acid solution of nickel and cobalt (which must be free from all other 
metals, save potassium or sodium) is nearly neutralised by potassic 
carbonate, and mixed with an excess of hydrocyanic acid, and then with 
pure caustic potash. The mixture is left exposed to the air in a shallow 
dish for some hours: a tripotassic cobalticyanide (K 3 CoCy 6 ) and a 
nickelo-potassic cyanide (2KCy, NiCy 4 ) are in this way produced. If 
this solution is now boiled with a slight excess of mercuric nitrate, 
hydrated nickelous oxide is precipitated, but potassic cobalticyanide 
remains in solution, and may be filtered off. On carefully neutralising 
the alkaline filtrate with nitric acid, and adding a solution of mercurous 
nitrate, the cobalt may then be precipitated as a mercurous cobalti¬ 
cyanide, which may be collected, washed, dried, decomposed by ignition, 
and weighed as cobaltous oxide. After obtaining both nickel and cobalt 
oxides, or either of them, they may be easily identified by the blowpipe. 
The oxide of nickel gives, in the oxidising flame with borax, a yellowish- 
red glass, becoming paler as it cools ; the addition of a potassium salt 
colours the bead blue. In the reducing flame the metal is reduced, 
and can be seen as little greyish particles disseminated through the 
bead. Cobalt gives an intense blue colour to a bead of borax in the 
oxidising flame. 
IV.—PRECIPITATED BY AMMONIUM SULPHIDE. 
Iron — Chromium — Thallium — Aluminium — Uranium. 
1. IRON. 
§ 913. It was Orfila’s opinion that all the salts of iron are poisonous, 
if given in sufficient doses ; but such salts as the carbonate, the phos¬ 
phate, and a few others, possessing no local action, may be given in such 
