LEAD 47 



(PJ,omb, Fr. ; Blei, Ger.) This metal appears to have been known at 

 a very early period. It is mentioned by Moses, as a metal in common use. Job 

 describes mining for lead, and the metallurgic processes of refining and separating 

 silver from lead are very clearly described by both Job and Jeremiah. Lead has a 

 bluish-grey colour, and, when recently cut, it exhibits considerable lustre, which, 

 however, it speedily loses. It is one of the softest of the ordinary metals, is easily 

 cut with a knife, may be scratched with the nail, and marks paper with a grey stain. 

 Lead is malleable, and may be beaten into thin leaves, but these are of very imperfect 

 tenacity ; hence, it cannot be drawn into thin wire ; a wire of ith of an inch in dia- 

 meter will not support 20 Ibs. 



If lead be prepared in a very finely divided state, it is pyrophoric. This is usually 

 prepared from the tartrate of lead, by heating it in a glass tube as long as any fumes 

 are evolved ; consequently, it is finely-divided lead, combined with some carbon. As 

 soon as the fumes cease, the tube must be closed at the blowpipe-lamp. If at anytime 

 the tube is broken, and the powder scattered in the air, it burns with a red flash. 



If lead is heated in closed vessels, it fuses at 635 F. (335 C.), and at a red 

 heat, it gives off vapours. If fused lead is allowed to cool slowly, it crystallises in 

 a somewhat peculiar manner ; the crystals are referrible to the cubic system, but 

 they groiip themselves in a very complicated and interesting way. By tie electro- 

 chemical action of zinc on a solution of the acetate of lead, crystals of that metal are 

 obtained in an arborescent form. This experiment is usually spoken of as the forma- 

 tion of Saturn's tree, Saturn being the alchemic name for this metal. 



When fused in the air, lead oxidises rapidly, and it becomes covered with an 

 iridescent pellicle, often of great beauty. It then passes into a yellow powder 

 (litharge), protoxide of lead. 



Pure lead is not affected by perfectly pure water free from air ; but if air be present, 

 the metal is oxidised at its expense, and the oxide thus formed, combining with 

 carbonic acid, is deposited on the lead in minute crystals aeftatiasic carbonate, of lead. 

 The water will then be found to contain lead in solution, and such waters drawn 

 from impure cisterns often produce very distressing consequences. If the water 

 contains any sulphates, the lead is thrown down as a sulphate of lead, which is 

 insoluble. 



The Ores of Lead. 



1. Native lead. Mr. Greg appears to doubt the existence of native lead in this 

 country. He says, however, ' Native lead has been recently discovered in undoubtedly 

 genuine specimens in the province of Guanaxiiato in Mexico.' Some equally genuine 

 specimens of native lead have been found in the Grassington mines and examined by 

 the Editor ; these are in the cabinets of the Duke of Devonshire, and of the late Stephen 

 Eddy, and it is now we presume in the possession of his son. 



2. Minium. Native oxide of lead. This rare ore has been found in Anglesea, at 

 Alston Moor, the Snailbeach Mine in Shropshire, at Grassington, the Leadhills in 

 Scotland, and Wicklow in Ireland. Its composition is lead, 90'66, oxygen, 9 - 34. 



3. Cerussite. Carbonate of had. White Lead ore (Bleispath, Ger.). This ore occurs 

 in cr} 7 stals. in fibrous, compact, and earthy masses. It is found at several of the lead 

 mines of Cornwall and Devonshire; remarkably fine specimens have been obtained 

 from Frank Mills Mines in Devonshire, one of which is in the Museum of Practical 

 Geology. In nearly all the mines producing the ores of lead, cerussite is formed, 

 varying much in its character with the different conditions under which it has been 

 formed. 



This ore, in its purest state, is colourless and transparent like glass. It may be 

 recognised by the following characters : Its specific gravity is from 6 to 6'7 ; it dis- 

 solves with more- or less ease, and with effervescence, in nitric acid ; becomes im- 

 mediately black by the-action of sulphuretted hydrogen, and melts on charcoal before 

 the blowpipe into -a button of lead. According to Klaproth, the carbonate of Leadhills 

 contains 82 parts of oxide of lead, and ] 6 of carbonic acid, in 98 parts. This mineral 

 is tender, scarcely scratches calcspar, and breaks easily with a waved conchoidal 

 fracture. It possesses the double refracting property in a very high, degree ; the 

 double image being very visible on looking through the flat faces of the prismatic 

 crystals. Its crystalline forms are very numerous, and are referrible to the rhombic 

 system. It is also found in an earthy state. 



4. Anqlesite. Sulphate of lead, or Vitreous lead (Bleivitriol, Ger.). This mineral 

 closely resembles carbonate of lead ; so that the external characters are inadequate to 

 distinguish the two. But the following are sufficient. It does not effervesce with nitric 

 acid ; it is but feebly blackened by sulphuretted hydrogen ; it first decrepitates and then 

 melts before the blowpipe into a transparent glass, which becomes milky as it cools. By 

 the combined action of heat and charcoal, it passes first into a red pulverulent oxide, 



