LEAD. 
§§ 804 - 806 .] 
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 hydro¬ 
chloric acid, and treated after filtration with SH 2 . Cadmium may also be estimated 
volumetricaily 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.—PRECIPITATE BY HYDRIC SULPHIDE IN HYDRO¬ 
CHLORIC ACID SOLUTION—BLACK. 
Lead—Copper—Bismuth—Silver—Mercury. 
1. LEAD. 
§ 804. 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., 0 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. 
Minium, or Red Lead, 2PbO, Pb0 2 —specific gravity, 9-08—is a 
compound of protoxide of lead with the dioxide. It is of a brilliant red 
colour, much used in the arts, and especially in the preparation of 
flint-glass. 
§ 805. Sulphide of Lead, PbS = 239—Pb 86-61 per cent. ; S 13-39 
per cent.—occurring in the usual way, is a black precipitate insoluble 
in water, dilute acids, alkalies, potassium cyanide, and alkaline sul¬ 
phides. It dissolves in strong nitric acid with separation of sulphur, 
and in strong hydrochloric acid with evolution of SH 2 . Fuming nitric 
acid does not separate sulphur, but converts the sulphide into sulphate. 
§ 806. Sulphate of Lead, PbSO 4 =303—specific gravity, 6-3 ; PbO 
73-61 per cent. ; S0 3 26-39 per cent.—when produced artificially, is a 
heavy white powder, of slight solubility in water, 22,800 parts of cold 
water dissolving only one of lead sulphate ; and if the water contains 
sulphuric acid, no less than 36,500 parts of water are required. Alkaline 
acetates, the acetate, tartrate, and citrate of ammonia dissolve the 
sulphate without change ; sodic hyposulphite dissolves lead sulphate, 
changing it partly into sulphite. The sulphate can be readily changed 
