Out of any surplus remaining in any given year, the directors shall each year set aside not less than ten percent of such savings for the accumulation of a reserve fund until such reserve shall equal at least forty percent of the invested capital of the association, not less than one percent nor more than five percent for a permanent educational fund from which expenditures shall be made annually at the discretion of the directors for the purpose of teaching cooperation, and the remainder to be returned to the members as a patronage dividend prorated on a uniform basis to each member upon the value of business done by that member through the association.