Red Lead

, RED LEAD. Red lead or miniema is an oxide of the metal; Niearge being another oxide. Litharge is produced in the process of cupellation, or the separation of the minute quantity of silver which most lead ores con. tain ; it is a refuse, so far as the immediate process is concerned; butit is afterwards used in making flint glass, or as a material whence many of the salts of lead, useful in the arts, are prepared.

lied Lead, however, is purposely manu factured, and the furnaces are adapted ex pressly for this purpose. It is one of the wonders of chemistry, to see this red pOwder produced simply by the action of the common air on melted metallic lead : it baffles all our usual conceptions concerning the production of colour, Pigs of lead, to the weight of about 30 cwt., are put into a reverberating furnace, and exposed to a melting heat. A man then stands before the open month the furnace, and keeps the molten lead continually moved by a sort of rake. This movement causes all parts of the metal to come successively in contact with the air, which enters at the open mouth of the furnace. In five or six hours

the lead thickens, and acquires the look of a grayish yellow powder ; it has become a mix ture of oxidized lead with lead which has not yet had sufficient contact of air to have become oxidized. The contents of the fur nace are then raked out, and when cold are ground in a mill to a fine state, and steeped in water. The lead particles sink, while par ticles of yellow oxide remain diffused in the water. The water is poured off, and allowed to settle, and the yellow oxide precipitates. This oxide, when collected and dried, consti tutes lifassicol ; and by again exposing it to the heat of a furnace, and allowing it to absorb more oxygen, the oxide changes its colour from yellow to red, and changes from Massicot to Red Lead.

This manufacture is carried on, among other places, at the lead works of Newcastle.