Pencils Rompecabezas de rompecabezas

When naturally occuring graphite was discovered, chemistry was in its infancy and the substance was thought to be a form of lead. Consequently, it was called plumbago (Latin for "lead ore") . The black core of pencils is still sometimes referred to as "lead," even though it never contained the element lead.

English | Français | 日本語 | Deutsch