The chemical name of white salt is Lead nitrate Pb(NO3)2.
The salt on heating produces brown fumes. This implies that the salt contains nitrate ion. This salt can be any nitrate but if the residue left after heating is yellow in colour implies that the salt is lead nitrate.
The equation involved can be shown as:
2Pb(NO3)2 → 2PbO + 4NO2 + O2
Lead nitrate Lead oxide Nitrogen dioxide
Colourless Yellow Brown fumes