Element Lead, Pb, Poor Metal
About Lead (Plumbum)
|Lead (Plumbum) is allied to strontium and barium in like manner as zinc and cadmium are allied to magnesium. Calcium, which exhibits relations of isomorphism in both directions, stands in the middle. On the other hand, lead is decidedly a heavy metal, and forms an insoluble, dark-coloured sulphur compound. |
In nature lead is fairly widely distributed. Its most important naturally occurring ore is lead sulphide, from which by far the largest amount of the metal is obtained. The carbonate and the sulphate, which are isomorphous with the corresponding salts of strontium and barium, are also found.
Metallic lead has been known from olden times, as it can be readily obtained from its ores. Its many applications depend, on the one hand, on its low melting point, 330°, and its great density, 11.4, and, on the other hand, on its softness and consequent plasticity. The last property renders it possible, especially at a somewhat higher temperature, to form lead by pressure like a plastic mass, and in this way to produce wire, tubing, and such like.
In moist air lead oxidises very rapidly, but only superficially, so that on the whole it is fairly resistant. It should be mentioned here that it resists the action of perfectly pure water much less than that of ordinary spring or river water. This is due to the fact that in the former case, under the joint action of water and atmospheric oxygen, lead hydroxide is produced, which is slightly soluble in water, and therefore does not protect the lead. In impure water, which contains sulphanion and carbanion, the corresponding lead salts are formed, which have an extremely small solubility, and form a firmly adhering layer on the lead. Thus lead pipes can be quite well used for the ordinary water-supply, but not for distilled water.
The combining weight of lead has been determined by the conversion of the metal into the oxide, and vice versa. It has been found to be Pb = 206.9.
|The origin of the modern Russian name "svinets" is not clear. In the past it was not always clearly distinguished from tin. In most of Slavic languages such as Bulgarian, Serbo-Croatian, Czech, and in Polish lead is called as tin, olovo. The word similar to Russian svinets is found in Baltic languages: the Lithuanian svinas and the Latvian swins. The English lead was borrowed from the Irish luaide of unknown origin which, according to many sources, derived from Celtic loud or Sanskrite loka, which means reddish, because of the red colour of lead oxide (red lead). Greeks called it molybdos; the same name is used also in Modern Greek language. The Latin molibdaena derived from the Greek word was assigned both to lead glance PbS as well as much more rare molybdenite MoS2 and all other substances which leave black marks on bright-coloured surface, similarly to graphite and lead itself. Lead could be used for writing; that is why the German for pencil is "ein Bleistift" which means lead. |
|Main article Lead Occurrence; |
Poor metal Lead, or Plumbum abundance is 1.6x10-3 mass % in the Earth's crust, 0.03 µg/l (41.1 million tons), and 0.2 - 8.7 µg/l in river water. Around 80 lead containing minerals, the main of which is galena PbS, formed in the Earth crust are associated mostly with hydrothermal deposits. Numerous (around 90) secondary minerals such as are formed in complex ores oxidizing zones plenty of minerals are formed such as sulphates (anglesite PbSO4), carbonates (cerussite PbCO3), phosphates (pyromorphite Pb5(CO4)3Cl). Lead is diffused in biosphere, with small content in living matter (5x10-5%) and in sea water (3x10-9%). It is partially accumulated by clays from natural waters and then is sedimented by hydrogen sulphide, so it is accumulated in the hydrogen sulphide contaminated sea ooze as well as in dilsh and slates formed in it.
In atmosphere its content reaches 2x10-9-5x10-4 µg/m3. In adult human body it contens is about 7-15 mg.