PLUMBAGO, a name frequently applied to graphite in allusion to its remote resemblance to lead, whence it is popularly called “black lead.” When Scheele, in 1779, examined this mineral he regarded it as a compound of carbon and iron, and consequently termed it a “carburet of iron”; but Vanuxem in 1825 showed that the iron existed in the form of an oxide, and was not essential to the constitution of the mineral—a conclusion also reached about this time bv Karsten. It thus became fully established that plumbago is simply an impure form of native carbon. Plumbago is principally used in the manufacture of “black-lead” pencils, for which purpose it was at one time very extensively worked at Borrowdale in Cumberland. It was known locally as “wad,” and a grant of the manor of Borrowdale, as far back as the reign of James I., refers to “the wad-holes and wad, commonly called black cawke.” The Cumberland plumbago is found in pipes, strings, and irregular masses known as “sops,” which occur in a dyke of diorite, associated with a compact blue diabase, penetrating some of the altered ash-beds of the volcanic series. Important mines of plumbago, yielding fine pencil lead, were opened some years ago by Μ. Alibert in the government of Irkutsk in eastern Siberia. A good deal of plumbago is also worked near Passau in Bavaria. The graphite so largely used, when mixed with fire-clay, in the manufacture of “black-lead” crucibles, is obtained chiefly from Ceylon; and it is notable that, notwithstanding the purity of the Ceylon plumbago, it is not applicable to the manufacture of lead pencils. Large quantities of plumbago occur in the Laurentian limestones of Canada; while in the United States the mineral is worked at Sturbridge, Mass.; at Ticonderoga and ...