Basic lead carbonate
source : patrickpaty.co.uk
White Lead or basic lead carbonate : [2PbCO3.Pb(OH)2]
Manufacture:
white lead or basic lead carbonate is manufactured by two methods:
1. Dutch process:
A number of perforated lead disc are taken and placed on the number of earthen layer pots. These pots are called aludel . Dil. CH3COOH (acetic acid) is taken in the bottom of aludels. Lead discs are kept on the aludels. A number of aludels containing acetic acid and lead disc are arranged in rows. These are covered in wooden planks. Bark or horse dung is placed on wooden planks and a room is filled with aludels and door is closed for two or three months then lead is converted into white lead.
2. Carter process:
This is a quick process, white lead is prepared in 15 days. CO2 and super heated stream is passed in molten lead then lead is converted into very small particles. A stray of CH3COOH and air containing CO2 is passed into wooden cylinder containing lead particles. Lead particles react with CO2, water, CH3COOH and air to form white lead.
Properties of basic lead carbonate or white lead:
1. It is white powder, insoluble in water but soluble in linseed oil.
2. It is poisonous.
3. It reacts with H2S in presence of air and became black due to formation of lead acetate (PbS).
Uses:
1) It is white pigment.
2) It is used in making paints.
Question : what is Lithopone ? How is it better than white lead ?
Lithopone is the mixture of BaSO4 and ZnS . It is used as white pigment in paints. It doesn’t turn black in presence of H2S and its covering power is also more.
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