Method to purify Lead for Affityhig. 1$ 



grain in the pound. It was therefore of no ufe for proofs by 

 fcorification and for aflaying ; and the principal point now 

 was to free the litharge from its mixture. This object I 

 accomplifhed by a few meltings, in the following manner ; 



I placed a crucible, in which half a pound of litharge 

 found good room, and which was fitted with a clofe cover, 

 in a wind-furnace filled with dead coals. I then put into 

 the crucible a mixture of four ounces of potafh and the 

 fame quantity of powder of Hint. When the whole was 

 well melted by ftrengthening the draught and making the 

 coals glow, I took off the cover, and laid hold of the cruci- 

 ble with a pair of tongs, in order to take it out, and to fuf- 

 fer this very fuiible glafs to cover the infide of the crucible, 

 to fecure it from the glafs of the lead which I meant to 

 melt in it. The fuperfiuous glafs was poured out; the 

 crucible again placed on its foot, and half a pound of li- 

 tharge thrown into it with a fhovel. The cover was placed 

 upon it while the litharge was melting ; and when' it was 

 thoroughly glowing and fluid, charcoal duft was lifted into 

 the uncovered crucible through a fieve, fo that the furface 

 of the litharge was completely covered with it. This im- 

 mediately produced an effervefcence, and the rifing of bub- 

 bles, by means of the fcparation of the air occafioned by 

 the reduction of the lead. During this procefs the cover 

 vp put on and a few coals thrown into the furnace : when, 

 thefe were burnt every thing in the crucible was quiet, and 

 the melted mafs was poured into a warm conical mould. 

 The crucible was then again filled with half a pound of 

 the fame kind of litharge, and put into the furnace, and 

 charcoal duft was feveral times lifted over the melted fur- 

 face, till it was well covered before the mafs was thrown 

 out, a fumcient fpace being every time left for the effervef- 

 cence. The firft mafs had, in the mean time, become cool, 

 and, on examination, contained four ounces of lead at the 

 bottom, and litharge at the top. When this litharge was 

 reduced with potafh and crude tartar, the lead thence ob- 

 tained, 



