BLACK LEAD
Cooley's Cyclopedia of Practical Receipts and Collateral Information · 1880 · p. 15
(lĕd). See Plumbago .
Bu kavram başka kaynaklarda da geçiyor
Hawkins' Electrical Dictionary (1915)
Everybody's Encyclopedia (1912)
A Dictionary of Arts, Manufactures and Mines (1840)
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