The county board of any county is authorized and empowered to appropriate, out of the revenue fund of such county or out of the proceeds from a special tax levy upon all the taxable property in the county, such sum as it may deem advisable, to be paid to the historical society of such county, to be used for the promotion of historical work within the borders thereof, and for the collection, preservation and publication of historical material, and to disseminate historical information of the county, and in general to defray the expense of carrying on the historical work in such county; provided that no county board is authorized to appropriate any funds for the benefit of any county historical society unless such society shall be affiliated with and approved by the Minnesota Historical Society.