Abstract: To study the composition change during melting of PbO-PbBr₂-PbF₂-P₂O₅ system glass, the quantitative chemical analysis was complied to measure the
composition of the glass after melting. The results show that the loss of lead during melting is mainly ascribed to the volatilization of PbBr₂. When a sample
contains a high content of phosphorus and a low content of fluorine, the loss of bromine and phosphorus is remarkable, mainly in the form of PBr₃. On the other
hand, if a sample contains a high content of fluorine and a low content of bromine or a low content of phosphorus, bromine will not lose much while a large amount
of phosphorus and fluorine are lost during melting, mainly in the form of PF₅. The reaction between phosphorus and fluorine is much easier than that
between phosphorus and bromine. The results of thermodynamic calculation are consistent with the above results and discussions. The content of oxygen is
influenced by two factors. Volatilization of P₂O₅ decreases the content of oxygen, while the reaction between oxygen or water in air and halides in
melts increases the content of oxygen.

Key words: glass, chemical analysis, volatilization form, chemical thermodynamic calculation