Lead

Lead is a mal­leable, low-melt­ing met­al of a sil­very-white col­or with a bluish tinge. It is quite soft: it can be cut with a knife and scratched with a fin­ger­nail. It is a rather heavy met­al, with a den­si­ty of 11.3415 g/cm³ at 20 °С.

In na­ture this met­al makes up 1.6•10⁻³ % of the mass of the earth’s crust, but is hard­ly ever en­coun­tered in its orig­i­nal form. Lead is a com­po­nent of 80 min­er­als in­clud­ing gale­na PbS, cerus­site Pb­CO₃ and an­gle­site Pb­SO₄ (lead sul­fate).

Lead in his­to­ry

Lead has been known since an­cient times. The smelt­ing of lead was once of the first met­al­lur­gi­cal pro­cess­es dis­cov­ered by hu­man­i­ty. Per­haps this is why the ori­gin of the name of this met­al is lost in the depths of time.

The first items made of lead date from 6,400 BCE. In An­cient Egypt, a stat­ue made of lead was found dat­ing from 3,100 – 2,900 BCE. Ad­di­tion­al­ly, the An­cient Egyp­tians used lead com­pounds as cos­met­ics. There are ex­am­ples of the use of gale­na (lead sul­fide), cerus­site (lead car­bon­ate) and phos­gen­ite (lead car­bon­ate with chlo­rine an­ions). Phos­gen­ite is quite a rare min­er­al, and the An­cient Egyp­tians made it ar­ti­fi­cial­ly.

The largest pro­duc­er and con­sumer of lead in an­tiq­ui­ty was the Ro­man Em­pire. Lead pro­duc­tion reached 80,000 tons a year! The An­cient Ro­mans main­ly made pipes from it, as the met­al was easy to roll and join. Ad­di­tion­al­ly, dish­es were made from lead. Lead was even added to wine to im­prove its taste! But Pliny and Vit­ru­vius warned that lead could poi­son the body. Grad­u­al poi­son­ing from lead com­pounds caused a drop in fer­til­i­ty, and dam­aged the brain and ner­vous sys­tem. Ac­cord­ing to some the­o­ries, this was one of the fac­tors that caused the fall of the Ro­man Em­pire.

In the Mid­dle Ages, peo­ple con­tin­ued to add lead to wine, caus­ing epi­demics of lead col­ic. In An­cient Rus­sia, church roofs were cov­ered in lead. The met­al was also used to make bul­lets and shot. Af­ter the in­dus­tri­al rev­o­lu­tion, lead was used in­creas­ing­ly for the man­u­fac­ture of tins for food, print­ing type etc. Ad­di­tion­al­ly, in 1921 the Amer­i­can en­gi­neer Thomas Midg­ley found that adding tetraethyl lead to petrol in­creased its oc­tane lev­el. De­spite the tox­i­c­i­ty of this fuel, it con­tin­ued to be used for a long time. Its man­u­fac­ture was ceased in the USA in 1986, and not un­til 2000 in EU coun­tries.

Use of lead

De­spite their tox­i­c­i­ty, lead and its com­pounds have found wide ap­pli­ca­tion.

Chem­i­cal sources of elec­tri­cal en­er­gy use lead bis­muthate, sul­fide and io­dide, lead chlo­ride, sul­fate and lead diox­ide

Ra­di­a­tion pro­tec­tion in nu­cle­ar re­ac­tors and med­i­cal de­vices (for pro­tec­tion from X-rays)

In elec­tron­ics lead al­loys are used as sol­ders, for fig­ure cast­ing and the man­u­fac­ture of ball bear­ings.

Lead chro­mate and ba­sic lead car­bon­ate car­bon­ate Pb(OH)₂•Pb­CO₃ are yel­low and white dyes re­spec­tive­ly.

In ge­ol­o­gy, the con­tent of lead iso­topes in min­er­als is de­ter­mined in or­der to es­tab­lish their age. The sta­ble iso­tope Pb-204 is both non-ra­dio­genic (of a nat­u­ral ori­gin, not as the re­sult of ra­dioac­tive de­cay) and ra­dio­genic (as the re­sult of the de­cay of ra­dioac­tive nu­clei). The amount of ra­dio­genic nu­clei de­pends on time, so the sum­ma­ry con­tent of lead iso­topes in rock can give in­for­ma­tion about its age.

But nowa­days, the use of lead is re­strict­ed in many ways be­cause of its tox­i­c­i­ty. Se­vere lead poi­son­ing caus­es cramp, faint­ing, and pains in the stom­ach and joints. Lead ac­cu­mu­lates in bones, and also in the liv­er and kid­neys. Over a long time, lead caus­es dam­age to the ner­vous sys­tem, men­tal re­tar­da­tion (es­pe­cial­ly to chil­dren) and chron­ic brain dis­eases.

Beethoven is be­lieved to have died from lead poi­son­ing. This also caused the death of the British ar­chi­tec­tural ex­pe­di­tion of John Franklin in 1845-1848.

Sources: Paul Par­sons, Gail Dixon — The Pe­ri­od­ic Ta­ble A vis­ual guide to the el­e­ments (p.190), Wikipedia/Lead, Wikipedia/Lead poi­son­ing