Dear Amr Hessein did you successfully prepare the Sodium Seleniosulfide (Na2SeSO3) following this process? I am preparing also the aqueous solution of Na2SeSO3 by reflux, and i want to know more about the color of the final aqueous solution of Na2SeSO3 after refluxing. Actually after around 5h i got a colorless solution with some black solid paste inside the three neck bulb. I guess the black solid paste is an excess of Se powder or something that i don't know. Can you help me with the description of your final solution after refluxing?
Actually I stoped working on this method for the same reason of incomplete Se fissolving you mentioned in addition to time consuming and laking repeatability.