LEAD. 
valued on account of the fine blue colour 
which it yields. 
LEAD, is a white metal, of a considerably 
blue tinge, very soft and flexible, not very 
tenacious, and consequently incapable of 
being drawn into fine wire, though it is ea- 
sily extended into thin plates under the 
hammer. Its weight is very considerable, 
being rather greater than that of silver. 
Long before ignition, namely, at about the 
540th degree of Fal.renheit’s thermometer, 
it melts ; and then begins to be oxyded if 
respirable air be present. In a strong heat 
it boils, and einits fumes; during which 
time, if exposed to the air, its oxydation 
proceeds with considerable rapidity. If 
melted lead be poured into a box previously 
rubbed with clialk, to prevent its action on 
the wood, and be continually agitated, it 
will concrete into separate grains, of con- 
siderable use in various raoclianical opera- 
tions, particularly that of weighing. Lead 
is brittle at the time of congelation. In 
this state it may be broken to pieces with a 
hammer, and the crystallization of its inter- 
nal parts will exhibit an arrangement in pa- 
rallel lines. 
This metal, during the progress of heat, 
first becomes converted into a dusky pow- 
der, which by a continuation of the heat 
becomes white, yellow, and afterw’ards of a 
bright red, inclining to orange colour, called 
minium, or red lead. The process requires 
considerable management with regard to 
the heat and access of air, in the making of 
red lea(J. Many days are required for this 
purpose. If the heat be too great or rapid, 
the lead becomes converted into a flaky 
substance, called litharge; and a still greater 
heat converts it into a clear, transparent, 
yellow glass, which powerfully dissolves and 
corrodes metallic oxides or earths ; and on 
this account it iisnally finds its way through 
the crucibles in a shot t time. It acts more 
difficultly on argillaceous than on siliceous 
earths ; v.heuce it is found that vessels 
made of clay mixed with broken pottery 
are preferable to those that are composed 
of clay and sand. The oxide of lead is 
a principal ingredient in most of the modern 
fine white glasses. It is more particularly 
calculated to form the dense glass used to 
correct the aberration arising from colour 
in those telescopes which are known by the 
name of achromatic, because it cnmmmii- 
cates the property of separating the colour- 
ed rays from each other in greater angles 
than obtain in alkaline glasses at equal 
angles cf ine.an refraction. The imperfec- 
tion which most considerably affects this 
kind of glass is, that its density is seldom 
uniform throughout. Tiie irregularities 
show themselves in the forms of veins, which 
greatly disturb the regular refraction. 
^ Lead is not much altered by exposure to 
air or water, though the brightness of its 
surface wdieu cut or scraped very soon goes 
off. It is probable that a thin stratum of 
oxide is formed on the surfiice, which de- 
fends the rest of the metal from corrosion. 
All the oxides of lead are very easily re- 
duced. Minium, when exposed to a strong 
heat, gives out part of the oxygen it ab- 
sorbed during its oxidation ; but, like the 
other oxides of this metal, it requires the ad- 
dition of some combustible substance for its 
complete revival : a familiar instance of this 
revival is seen by exposing the common wa- 
fers to tlie flame of a candle. The w afers are 
coloured with minium,whicli is revived by the 
heat and inflammable substance of the wafer, 
so that it fails down in metallic globules. 
Lead is found native, though seldom ; and 
also in the form of an oxide, called native 
cerr.se, or lead ochre, or lead spar of vari- 
ous colours, red, brown, yellow, green, 
blueisii, and black. These ores, when 
freed as much as possible from earthy mat- 
ter, may be di.ssolved in diluted nitrous 
acid. Oxide of iron is usually thrown down 
from the solution by boiling. If the lead 
be then precipitated by t!:e carbonate of 
soda, and weighed, 133 grains of the dry 
precipitate will correspond with 100 grains 
of lead in the metallic state. If the preci- 
pitate be suspected to contain copper, it 
may be separated by digesting in amiuonia. 
If it be supposed to contain silver and cop- 
per, the precipitate may again be dissolved 
in nitric acid, and sepa-^ated by the uddiLiou. 
of muriatic acid ; which combining with the 
metal, produces the muriates of silver, and 
of lead; 'the latter of which being soluble 
in thirty times its weiglit of boiling water, 
may be washed off', while the silver remains 
undissolved ; or the silver, if alone in the 
precipitate, may be taken up by ammonia, 
wliich will leave the oxide of lead of the 
same value, with regard to weight as the fore- 
going. 
Lead is also found mineralized by the 
sulp'mric and the phosphoric acids ; this 
last is of a greenish colour, arising irom a 
mixture of iron. The sulphate of lead is 
soluble, in about eighteen times its weight 
of W'aler. One hundred and forry-lhree 
gfains of the dried salt represent 100 grains 
of lead. Thephosphate oflead ore may be 
