Which is a good COD digester

The JC-103C high chlorine standard COD digester is a high range digester produced by Juchuang Environmental Protection. During the measurement, a known amount of potassium dichromate solution and mercury sulfate solution are added to the water sample, and silver sulfate is used as a catalyst in a strong acid medium. After boiling and refluxing for 2 hours, 1,10-phenanthroline is used as an indicator to titrate the unreduced potassium dichromate in the water sample with sulfur ferrous ammonium. The apparent COD is calculated by converting the amount of sulfur ferrous ammonium consumed into the mass concentration of oxygen consumed.