Abstract: A method is taught for increasing the yield of anhydrous sodium dithionite by adding an organic compound that is thiosulfate reactive to a batch reactor containing a puddle solution of methanol and fed with formic acid or an alkali formate as a first feed, an aqueous alkali compound as a second feed, an aqueous alkali formate solution as a third feed, and a methanolic SO.sub.2 solution as a fourth feed. This organic compound may be added prior to, combined with, or concurrently with one of the four feeds to the reactor. Preferably, it is added concurrently with the third feed and throughout the entire course of the reaction, ending with the beginning of the cooling period. A suitable addition rate is 0.4-0.6 wt. %/minute, preferably 0.5 wt. %/minute. All of the organic compound is consumed, and at least a portion of the thiosulfate ion is destroyed.