Chai*. II.
COMPOSITION AND USE OF MINERALS.
G59
metallic lead being obtained. At a high red heat it ftiscmand forms what is termedlitharge, which is a lamellar vitreous mass of reddish brown colour.
Lead - - - I - 104
Oxygen - - - 1 8 -
92-857
7-143
1 112
100-000
Deutoxide of Leach Red Lead , Minium , is a common red pigment,the protoxide to the action of heat at 700°, and air sufficient toit; its fine red colour loses its brilliancy by exposure to light.
produced by exposingoxidise without fusing
Oxygen - - 1 ^ 12
89-66
10-34
I 116
100 00
Peroxide of Lead. —Lead 104 with oxygen 16 = 120.
Chloride of Lead is obtained by heating laminated lead in chlorine; the gas is absorbed,and chloride of lead is formed; its specific gravity is 5*13.
Patent Yellow is formed from the compound of chloride and oxide of lead.
Lead - - 1 - 104 -
Chlorine - - 1 36
74-3
25-7
1 140
100 0
Sulphuret of Lead , the galena of mineralogists, is found native, and is the chief sourcewhence pure lead is obtained; its primitive form is that of the cube; it often contains asufficient quantity of silver to be worth extracting. Galena is reduced by a simple pro-cess ; the ore is broken and washed, then roasted in a reverberatory furnace, the temper-ature being sufficient to soften but not to fuse it. When the fumes of the sulphur aredriven oft' it is then fused ; the lead sinks to the l>ottom of the fuel which has reducedit, and is run out and moulded into pigs. Sulphuret of lead has a colour and lustre
resembling pure lead; it is brittle, and
requires a
white heat for fusion; its specific gravity
is 7-58.
Load
- 1
104
86-66
Sulphur
- 1
16
13-34
1
120
100-00
Sulphate of Lead in its native state is
crystallised into prisms
and octohedra.
Oxide of lead
- 1
112
73-68
Sulphuric acid
- 1
40
26-32
1
152
100-00
Carbonate of Lead , White Lead , or Ceruse , is prepared by exposing sheet lead to the actionof the vapour of vinegar, or by decomposing the acetate of lead by a carbonate; its specificgravity is 6-4: when found native it is one of the most beautiful of metallic ores; it is softand brittle, sometimes tinged with carbonate of copper, and has a green colour ; its primitiveform is the octohedron, though it is found prismatic and tabular.
Oxide of lead - - 1 - 112 - 83*58
Carbonic acid - 1 22 16-42
1 134 10000
Alloys of Lead. — Plumbers Solder contains equal parts of lead and tin, or, according toothers, two of lead and one of tin. Mirrors are made in Sweden containing 0-39 of lead,and 61 of tin. Common pewter consists of 80 parts of tin and 20 of lead.
Of the Mines that produce Lead —Northumberland, Durham, and Cumberland. Thiscountry, although politically distributed amongst the three counties, is one and the same inall its characteristic features. From it flow the Tyne, the Wear, and the Tees , and manybranches which fall into these rivers. Along their banks are dales or valleys highly cul-tivated, but beyond them rise dark fells, covered with peat moss and heath, and betweenone vale and another is a wide range of high moorland, extending sometimes for manymiles. In these upland districts are no inhabitants; thousands of black-faced sheep arescattered over them, and grouse are found in abundance.
The rivers do not, as in rich, flat, clayey lands, form for themselves a winding serpentinecourse, but flow onward in a straight line, and with a rapid current. The channel, of
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