B34 Process for making White Lead. 



more or less. The surface then becomes a little irregular^ 

 and full of points; which is favourable to the oxidation that 

 follows. On this operation we need not insist, the process 

 being already well known. 



The second operation consists in oxidizing and carboni- 

 zing the lead. The following is the disposition of the ap- 

 paratus : 



AI. Montgolfier had a common chemical reverberatory 

 furnace, in which he burned charcoal. The chimney on 

 its dome was four or five metres high, and, taking a hori- 

 zontal direction, was introduced into an opening in the end 

 of a cask (which lay on its side) a little above its centre. 

 Some vinegar was put into the lower part of this cask, and 

 towards the centre of its other end was adjusted another 

 tube, equal to the chimney, and communicating by its 

 other extremity with a large rectangular case in which were 

 suspended the sheets of lead, alternately high and low, that 

 the air might pass entirely over their whole surface. 71ie 

 other end of this case had an opening to allow the redun- 

 dant gas to escape. The case had a cover, which could be re-, 

 moved at pleasure, for the purpose of placing the sheets of 

 lead on small pieces of wood prepared to receive them. 



The air from the furnace, being thus made to pass through 

 the cask containing the vinegar, by communicating heal to 

 the vinegar carries it off in vapour, and passes with it 

 through the case containing the sheets of lead, which of 

 course are exposed to the action of acetous acid, of car- 

 bonic acid from the combustion of the charcoal, and of 

 oxygen and azote, or atmospheric air which has escaped 

 the action of the fuel, and which may be augniented at 

 pleasure by leaving holes towards the middle of the chim- 

 ney to admit fiesh atmospheric air. Thus are combined 

 all the circumstances necessary to the produciion of car- 

 bonate oi lead — oxygen, carbonic acid, vinegar, and heat. 



In a short time the sheets of lead become charged with 

 a coat of carbonate. If their entire conversion into car- 

 bonate at a smgie operation is not intended, they are with- 

 drawn from the case, and suspended in water : the white 

 lead readily detaches itself, and falls to the bottom. If the 

 sheets are left till wholly converted into carbonate, still 

 they must be put in water; and, besides, the deposit must 

 be levigated to separate the metallic particles which may 

 have escaped oxidation, atid which would tarnish the white 

 colour. 



XL. Jn 



