When crystals of lead nitrate are heated strongly in a dry test tube

$2\text{Pb}{\left({\text{NO}}_{\text{3}}\right)}_{\text{2}}\left(\text{s}\right)\to 2\text{PbO}\left(\text{s}\right)+4{\text{NO}}_{\text{2}}\left(\text{g}\right)+{\text{O}}_{\text{2}}\left(\text{g}\right)$

When crystals of lead nitrate is heated brown fumes appear in the tube. PbO residue is also left.