Some Observations Concerning the Substance Commonly Called, Black-Lead, by the Late Dr. Rob. Plot, F. R. S.

periments, as seem to promise a full Decision in this Matter. VI. Some Observations concerning the Substance commonly called, Black-Lead, by the late Dr. Rob. Plot, F. R. S. THE Mineral Substance, called, Black Lead (our common Lead being the true Black Lead, and so called, in Opposition to Tin, which is the White Lead) found only at Keswick in Cumberland, and there called, Wadt, or Kellow; by Dr. Merret, Nigrica Fabrilis, from its use in Scoring, as the Rubrica Fabrilis, or the Red Ochre is; is certainly so far from having any thing of Metal in it, that it has nothing of Fusion, much less Ductility; nor can it be reckoned amongst the Stones, for want of Hardness; it remains therefore that it must have Place amongst the Earths, tho' it dissolve not in Water, as most Earths will, except stiff Clays, and Ochres; among the latter whereof I guess it may be reckoned, it seeming to be a sort of close Earth, of very fine and loose Parts, so burnt that it is become Black and Shining, discolouring the Hands, as all the Ochres do; whence the most Proper Name that can be given it, perhaps, may be Ochra Nigra, or Black Ochre, being a Stony Sort, as there are Stony Sort of the Red and Yellow Ochres, as well as Clay.