The video illustrates a peritectic phase transformation for a Pb/Bi alloy with the peritectic composition. The system starts in the liquid phase and cools into the two phase Pb + L zone. The peritectic invariant reaction: Pb + L -> e takes place at the peritectic invariant temperature. In this process, the Pb and the liquid react to form the e-alloy with the peritectic composition. Once the reaction is complete, the e phase cools to room temperature and no further phase changes occur.