LEAD. 



toloured cubical masses, whose corners 

 are usually truncated ; its texture is lami- 

 nated, and its hardness variable. This is 

 called galena, or potter's lead ore. Most 

 lead ores contain more or less of silver. 

 When antimony enters into its composi- 

 tion, the texture is radiated or filamen- 

 tous. There are also lead pyrites, which 

 contain a considerable proportion of iron 

 and sulphur ; and red lead spar, which 

 consists of lead mineralized by sulphur 

 and arsenic : this is very scarce. 



If sulphuretted lead be boiled in nitric 

 or muriatic acid of a moderate strength, 

 the sulphur may be obtained pure, and 

 collected on a filter. When iron or stony 

 particles are contained among the undis- 

 solved part, the sulphur may be separated 

 by digestion in a solution of pure fixed 

 alkali, which converts it into sulphuret, 

 and leaves the other insoluble matters 

 behind. If the first solution be made 

 with nitric acid, it may contain silver and 

 lead, which, after precipitation by carbo- 

 nate of soda, may be separated by ammo- 

 nia, as mentioned in the humid anal} sis 

 of the calci form ores ; when the muriatic 

 acid is used for the solution of the ore, a 

 large quantity of muriate of lead sepa- 

 rates, for want of a sufficient quantity of 

 water to dissolve it. This requisite quan- 

 tity of water must be added to dissolve the 

 salt, before the precipitate is made by the 

 fixed alkali. 



All the ores of lead, except the phos- 

 phoric, are reducible to the metallic state, 

 by dissipating their volatile contents by 

 the blow-pipe on a piece of charcoal. In 

 the large way, they are reduced by fusion 

 with charcoal. 



The ores of this metal are Abundantly 

 found in the mine counties-*of England, 

 and in various other parts of the globe. 

 Its uses are numerous, and scarcely need 

 be mentioned. Its oxides are of great 

 use as a pigment, and in the manufacture 

 of glass. Lead is cast into thin sheets for 

 covering buildings, making- water-pipes, 

 and various other uses ; and this is rolled 

 .between two cylinders of iron, to give it 

 the requisite uniformity and thinness. 

 Lead is thought, and with some reason, 

 to be not perfectly innocent, even for 

 water pipes, and much less so for any 

 other kind of vessels. The workmen in 

 any of the preparations of lead are gene- 

 rally subject to a peculiar colic, and para- 

 lytic disorders, which most probably arise 

 from the internal use of the metal ;" for it 

 is a fact, that_the,se workmen are not suf- 

 ficiently cautious in washing their hands, 

 or removing such particles 'of lead, or its 

 preparations, as may c usually intermix 

 with their food. 



VOL. IV. 



Most of the acids attack lead. The si 1 1- 

 phuric acid scarcely acts upon it, unless 

 it be concentrated and boiling. Sul- 

 phurous acid escapes during the process, 

 the acid being decomposed. When the 

 distillation is carried on to dry ness, a 

 saline white mass remains, a small portion 

 of which is soluble in water, and is the 

 sulphate of lead : it affords crystals. The 

 residue of the white mass is an oxide of 

 lead. 



Nitric acid acts strongly 011 lead, and 

 converts it into a white oxide, if the acid 

 be concentrated; but if it be more di- 

 luted, the oxide is dissolved, and forms 

 nitrate of lead, which is crystallizable, and 

 does not afford a precipitate by cooling. 

 It detonates on ignited coals. Lime and 

 alkalies decompose the nitrous solution of 

 lead. The sulphuric acid added to this 

 solution combines with the metallic oxide, 

 and falls down. The muriatic acid in t!ie 

 same manner carries down the lead, and 

 forms a combination, which is more 

 soluble in water tluui the muriate of 

 silver. 



Muriatic acid acts directly, but sparing- 

 ly, on lead by heat, which it oxides, and 

 dissolves in part. The muriate of lead is 

 crystallizable. 



The acetic acid dissolves lead and its 

 oxides ; though the access of air or oxy- 

 gen seems necessary for the solution of 

 the metal itself in this acid. White lead, 

 or ceruse, is made by rolling leaden plates 

 spirally up, so as to leave the space of 

 about an inch between each coil, a:;d 

 placing them vertically in earthen pots, 

 at the bottom of which is some good vine- 

 gar. The pots are to be covered, and 

 exposed for a length of time to a gvntle 

 heat in a sand bath, or by bedding' them 

 in dung. The vapour of the vinegar, as- 

 sisted by the tendency of the lead to 

 combine with the oxygen of the air which 

 is present, corrodes the lead, and con- 

 verts the external portion into a white 

 oxide, which comes off in flakes when the 

 lead is uncoiled. The plates are thus 

 treated repeatedly, until thev are cor- 

 roded through. Ceruse, is the only white 

 substance used in oil paintings. It may 

 be dissolved without difficult}-, in the 

 acetous acid, and affords a ciystaliizablc 

 salt, called sugar of lead, from its sweet 

 taste. This, like all the preparations <;f 

 lead, is poisonous. 



The sulphurets preclpit^-v )<-:*(! from 

 its solutions, the BitlplYUf fall:! 1 .; cl 

 combination with the lead. Pure ail; a- 

 line solutions dissolve a small portion of 

 lead, and corrode a considerable quanti- 

 ty : the solution is said to give a black co- 

 lour to the hair. 



