reaction tank 12 is in the acid range and is for instance ph 2 as a result of the reaction na 2 so 4 is produced in accordance with the following representative formulae 3 na 2 so 3 3 h 2 so 4 2 h 2 cro 4 u2192 cr 2 so 4 3 3 na 2 so 4 5 h 2 o 1 6 na 2 s 2 o 3 6 h 2 so 4 2 h 2 cro 4 u2192 cr 2 so 4 3 3 na 2 so 4 3 na 2 s 4 o 6 8 h 2 o 2 3 na 2 s 2 o 5 3 h 2 o lt gt 6 nahso 3 6 nahso 3 2 h 2 cro 4 u2192 cr 2 so 3 3 3 na 2 so 4 5 h 2 o 3 3 na 2 s 2 o 5 2 h 2 cro 4 u2192 cr 2 so 3 3 3 na 2 so 4 3 2 h 2 o 3 na 2 s 2 o 4 3 h 2 so 4 4 h 2 cro 4 u2192 cr 2 so 4 3 cr 2 so 3 3 3 na 2 so 4 7 h 2 o.