LEAD. 
3.0 oxide of iron 
2.0 water 
100.0 
Prom the experiments of Morveau, it ap- 
pears that the colouring matter of lazulite is 
sulphuret of iron. 
LEAD, one of the perfect metals, appears 
to have been very early known. It is men- 
tioned several times by Moses. The antients 
seem to have considered it as nearly related 
to tin. It is of a blneish-white colour; and 
when newly melted is very bright, but it 
soon becomes tarnished by exposure to the 
air. It lias scarcely any taste, but emits on 
friction a peculiar smell. It. stains paper or- 
the lingers of a blueish colour. When taken 
internally, it acts as a poison. Its hardness 
is 5^; its specific gravity is 1 1 .33^3. Its 
specilic gravity is not increased by hammer- 
ing, neither does it become harder, as is the 
case with other metals ; a proof that the hard- 
ness which metals assume under the hammer 
is in consequence of an increase of density. 
It is very malleable, and may be reduced to 
very thin plates by the hammer ; it may be 
also drawn out into wire, but its ductility is 
not great. Its tenacity is such, that a lead 
wire only T *_ inch diameter is capable of 
supporting 18 pounds without breaking It 
melts, according to sir Isaac Newton, when 
heated to the temperature of 540° Fahren- 
heit : but Morveau makes its fusing point as 
high as 594°. When a very strong heat is ap- 
plied, the metal boils and evaporates, if it is 
cooled slowly, it crystallizes. The abbf . 
Mongez obtained it in quadrangular pyra- 
mids, lying on one of their sides. Each py- 
ramid was composed apparently of three 
layers. Pajot obtained it in the form oi a 
polyhedron with 32 sides, formed by the con- 
course of six quadrangular pyramids. 
When exposed to the air, it soon loses its 
lustre, and acquires first a dirty-grey colour, 
and at last its surface becomes almost white. 
This is owing to its gradual combination with 
oxygen, and conversion into an oxide; but 
this conversion is exceedingly slow ; the ex- 
ternal crust of oxide, which forms first, pre- 
serving the rest of the metal for a long time 
from the action of the air. 
Water has no direct action upon lead ; but 
it facilitates the action of the external air. 
For when lead is exposed to the air, and kept 
constantly wet, it is oxidated much more ra- 
pidly than it otherwise would be. Hence the 
reason of the white crust which appears upon 
the sides of leaden vessels containing water, 
just at the place where the upper surface of 
the water usually terminates. 
No less than four different combinations 
of lead with oxygen are at present known, 
though some of them have not been examin- 
ed with much attention. 
1. 'The protoxide, or first oxide of lead, 
may be obtained by dissolving lead in nitric 
acid, and boiling the crystals which that solu- 
tion yields by concentration along with 
pieces of metallic lead. The consequence is 
the formation of scaly crystals of a yellow co- 
lour, brilliant, and very soluble 'in water. 
These crystals are composed of the protoxide 
of lead combined with nitric acid. The pro- 
toxide may be precipitated by means of po- 
tass. Its properties have not hitherto been 
examined. It contains but a small propor- 
tion of oxygen. 
C. The deutoxide of lead may be formed 
by dissolving the metal in nitric acid, and 
pouring potass into the solution. A yellow- 
coloured powder is obtained, which is the 
deutoxide of lead. This oxide is composed 
of 91 parts of lead, and 9 of oxygen. When 
lead is kept melted in an open vessel, its sur- 
face is soon covered with a grey-coloured 
pellicle. Whtfn this pellicle is removed, 
another succeeds it ; and by continuing the 
heat, the whole of the lead may soon be con- 
verted into this substance. If these pellicles 
are heated and agitate ! for a short time in an 
open vessel, they assume the form of a green- 
ish-grey powder. Mr. Proust has shewn that 
this powder is a mixture of deutoxide, and a 
poriicn of lead in the metallic state. It owes, 
its green colour to the blue and yellow pow- 
ders which are mixed in it. It we continue 
to expose this powder to heat ior some time 
longer in an open vessel, it absorbs more 
oxygen, assumes a yellow colour, and is then 
known in commerce by the name of massi- 
cot. The reason of this change is obvious. 
The metallic portion of the powder gradually 
absorbs oxygen, and the whole of course is 
converted into deutoxide. 
When thin plates of lead are exposed to 
the vapour of warm vinegar, they are gradu- 
ally corroded, and converted into a heavy 
white powder, used as a paint, and called! 
wlnte lead. T his powder used formerly to i 
be considered as a peculiar oxide of lead ; ! 
but it is now known that it is a compound of 
the deutoxide and carbonic acid. 
3. If massicot ground to a fine powder is 
put into a furnace, and constantly stirred j 
while the flame of the burning coals plays 1 
against its surface, it is in about 48 hours 
converted into a beautiful red powder, known 
by the name of minium, or red lead. This 
powder, which is likewise used as a paint, 
and for various other purposes, is the tritoxide 
or red oxide of lead. 
4. If nitric acid, of the specific gravity 
1 .260, is poured upon the red-coloured oxid'e 
of lead, 185 parts of the oxide are dissolved; 
but 15 parts remain in the state of a black, or 
rather deep-brown, powder. This is the per- 
oxide, or brown oxide of lead, lirsl discover- 
ed by Scheele. The best method of prepar- 
ing it is the following, which was pointed out 
by Proust, and afterwards still farther im- 
proved by Vauquelin. Put a quantity of red 
oxide of lead into a vessel partly filled with 
water, and make oxymuriatic acid gas pass 
into it. The oxide becomes deeper and 
deeper coloured, and is at last dissolved. 
Pour potass into the solution, and the brown j 
oxide of lead precipitates. By this process 
68 parts of brown oxide may be obtained for 
every 100 of red oxide employed. This 
oxide is composed of about 79 parts of lead 
and 21 of oxygen. It is of a brilliant flea- 
brown colour. When heated it emits oxygen 
gas, becomes yellow, and melts into a 'kind 
of glass. When rubbed along with sulphur in 
a mortar, it sets the sulphur on fire, and 
causes it to bum with a brilliant flame. When 
heated on. burning coals the lead is reduced. 
All the oxides of lead are very easily con- 
verted into glass; and in that state they oxi- 
dize and combine with almost all the other 
metals except gold, platinum, and silver. , 
This property renders lead exceedingly use- 1 
ful in separating gold and silver from the j 
baser metals with vvhic^ they happen to be | 
contaminated. The geld or silver to be pu- 
rified is melted along with lead, and kept for 
some time in that state in a flht cup, called a 
cupel, made of burnt bones, or Uie ashes of 
wood. The lead is gradually vitrified, and 
sinks into the cupel, carrying along with it: 
all the metals which wer’e mixed with the 
silver and gold, and leaving these metals on 
the cupel in a state of purity. This process 
is called cupellation. The lead employed is- 
afterwards extracted from (he cupels, 'and is 
known in commerce by the name of litharge. 
It is a half-vitrilied substance, of a high red 
colour, and composed of scales, ft is merely 
an oxide of lead more or less contaminated 
with the oxides of other metals. But the 
best litharge is made by oxidizing lead di- 
rectly, and then increasing the heat till the 
oxicle is fused. The more violent the fusing 
heat, tiie whiter is the litharge. 
Lead has not yet been combined with car- 
bon, nor hydrogen; but it combines readily 
with sulphur and phosphorus, 
1. Sulphuret of lead may be formed either 
by stratifying its two component parts, and 
melting them in a crucible, or by dropping 
sulphur at intervals on melted lead. The 
sulphuret of lead is brittle, brilliant, of a deep 
blue-grey colour, and much less fusible than 
lead. These two substances are often found 
naturally combined ; the compound is then 
called galena, and is usually crystallized in 
cubes. Sulphuret of lead is composed, ac- 
cording to the experiment of Wenzel, of 
86.8 parts of lead and 13.2 of sulphur. 
2. Phosphuret of lead may be formed by 
mixing together equal parts of filings of lead 
and phosphoric glass, and then fusing them 
in a crucible. It may be cut w ith a knife, 
but separates into plates when hammered. It 
is of a silver-white colour with a shade of 
blue, but it soon tarnishes when exposed to 
the air. This phosphuret may also be form- 
ed by dropping phosphorus into melt; d lead. 
It is composed of about 12 parts of phospho- 
rus, and 88 oflead. 
Lead does not combine with azotic gas. 
Muriatic acid gradually corrodes it, and con- 
verts it into a white-coloured oxide. 
Lead is capable of combining with most of 
the metals. * 
1 . Lead may be easily alloyed with gold 
by fusion. The colour of the gold is injured, 
and its ductility diminished. This alloy is of 
no use; but it is often formed in order to pu- 
rify gold by cupellation. 
2. Platinum and lead unite in a strong 
heat : the alloy is brittle, of a purplish colour, 
and soon changes on exposure to the air. 
Many experiments have been made with this 
alloy, in order, if possible, to purify platinum 
from other metals by cupellation, as is done 
successfully with silver and gold : but scarcely 
any of the experiments have succeeded ; be- 
cause platinum requires a much more violent 
heat to keep it in fusion than can be easily 
given. 
3. Silver is often alloyed with lead in order 
to purify it by cupellation. This alloy is 
very fusible, much sotter than silver, and has 
much less tenacity, elasticity, and sonorous- 
ness ; its colour is nearly that of lead, and its 
specific gravity greater than the mean density 
of the metals alloyed. 
4. Mercury amalgamates readily with lead 
in any proportion, either by triturating it with 
lead lilmgs, or by pouring it upon melted 
