For the purpose of this chapter, any county within this state may be considered a state agency for the purpose of purchasing gasoline, oil, and other motor fuels, and batteries, tires, and tubes for motor vehicles. Any county purchasing agent within this state may, by complying with Acts 1955, No. 313, §§ 13, 14 [repealed], purchase such commodities through the state purchasing agent under the authority set forth in these statutes.