Preparation of anti-phage agent

Immediately prior to use, transfer 3.3 ml of 13% PRE added to 7 ml of freshly prepared ferrous sulphate solution (0.01%). After about 30 s the colour of the mixture changes to greenish then to black. These mixtures of ferrous sulphate and PRE should be protected from light. 

NOTE: The mixture is active for 45 min after preparation.