i 2 Red Lead. [Book VI. 



almoft the whole of the lead may be converted into 

 - a greyilh powder tinged with green and yellow. 

 This powder, being ground in a mill and waflied s 

 becomes of a more yellow colour. By further expo- 

 fure to a moderate heat, afiifted by the reverberation of 

 the flame of the fuel on the furface of this calx, it 

 gradually afiumes an orange, and then a bright red 

 colour, and is thus, in about forty-eight hours, con- 

 verted into the fubftance called minium, or red lead. 

 If lead is, in the phrafe of the chemifts, urged with a 

 more violent and fudden heat, the appearances which 

 it exhibits are different. It is firft converted into a 

 flaky fubftance, called litharge, which by the procefs 

 juft defcribed, may be converted into minium, but 

 which, by an increafe of heat, becomes fluid, and acts 

 fo powerfully as a folvent on earthy fubftances as 

 quickly to make its way through ordinary crucibles. 



All thefe calces of lead may be eafily reduced to 

 the metallic ftate, by melting them in contact with 

 inflammable fubftances. In calcining and reducing 

 fixty hundred weight of lead, there is found to be a lofs 

 of eighr hundred. This lofs was explained by the old 

 chemifts on the fuppofition of the eicape of a volatile 

 fubftance called by them mercurial earth, but which 

 was never proved to have any exiftence. The lofs, 

 however, ought to be attributed in fome meafure to 

 the evaporation of part of the lead itfelf, and partly 

 to the imperfection of the procefs, as it is feldom 

 performed fo accurately as to reduce the whole of ths 

 calx. 



Lead is very rarely found native. It is fometimes 

 found in the form of a calx, called native cerufe, or 

 lead ochre, or in that of lead fpar of various colours, 

 and which are in general either rhomboidal or cubical, 

 combined with fulphur is called galena, which 



