(3) The carbonate thus obtained, heated on platinum foil, is changed into the brown-red non-volatile oxide.
(4) The oxide behaves on charcoal as already detailed.
(5) A metallic portion can be obtained by melting the oxide with cyanide of potassium; it is between zinc and tin in brilliancy, and makes a mark on paper like lead, but not so readily. There are many other tests, but the above are conclusive.
If cadmium in any case be specially searched for in the organs or tissues, the latter should be boiled with nitric acid. The acid solution is filtered, saturated with caustic potash, evaporated to dryness, and ignited; the residue is dissolved in dilute hydrochloric acid, and treated after filtration with SH2. Cadmium may also be estimated volumetrically by digesting the sulphide in a stoppered flask with ferric chloride and hydrochloric acid; the resulting ferrous compound is titrated with permanganate, each c.c. of a d.n. solution of permanganate = ·0056 grm. of cadmium.
II.—PRECIPITATED BY HYDRIC SULPHIDE IN HYDROCHLORIC ACID SOLUTION—BLACK.
Lead—Copper—Bismuth—Silver—Mercury.
1. LEAD.
§ 772. Lead, Pb = 207.—Lead is a well-known bluish-white, soft metal; fusing-point, 325°; specific gravity, 11·36.
Oxides of Lead.—The two oxides of lead necessary to notice here briefly are—litharge and minium.
Litharge, or Oxide of Lead, PbO = 223; specific gravity, 9·2 to 9·5—Pb 92·82 per cent., O 7·18—is either in crystalline scales, a fused mass, or a powder, varying in colour (according to its mode of preparation) from yellow to reddish-yellow or orange. When prepared below the temperature of fusion it is called “massicot.” It may be fused without alteration in weight; in a state of fusion it dissolves silicic acid and silicates of the earths. It must not be fused in platinum vessels.