BOOK XXXIV. L. 170-L11. 172 



tremely efficient, while for creeping or foul iilcers ash 

 of calcined lead is useful ; and the benefit they 

 produce is on the samc lines as in the case of sheets 

 of papyrus." The lead is burnt in small sheets 

 mixed with sulphur, in shallow vessels, being stirred 

 with iron rods or fennel stalks till the molten metal 

 is reduced to ashes ; then after being cooled ofF it is 

 ground into powder. Another process is to boil 

 lead filings in a vessel of raw earth in furnaces till the 

 earthenware is completely baked. Some mix with 

 it an equal amount of lead acetate ^ or of barley and 

 grind this mixture, in the way stated in the case of § I68. 

 raw lead, and prefer the lead treated in this way to 

 the Cyprus slag. 



LI. The dross of lead is also utiUzed. The best 

 is that which approximates in colour most closely to 

 yellow, containing no remnants of lead or sulphur, 

 and does not look earthy. This is broken up into 

 small fragments and washed in mortars till the water 

 assumes a yellow colour, and poured ofF into a clean 

 vessel, and the process is repeated several times till 

 the most valuable part settles as a sediment at the 

 bottom. Lead dross has the same effects as lead, 

 but to a more active degree. This suggests a remark 

 on the marvellous efficacy of human experiment, 

 which has not left even the dregs of substances and 

 the foulest refuse untested in such numerous ways ' 



LII. Slag ^ is also made from lead in the same 

 way as from Cyprus copper ; it is washed with rain j 123 sqq. 

 water in linen sheets of fine texture and the earthy 

 particles are got rid of by rinsing, and the residue 

 is sifted and then ground. Some prefer to separate 

 the powder with a feather. and to grind it up with 

 aromatic wine. 



