On or before the first day of September in each year, the county treasurer shall make out a list of the unpaid delinquent personal property taxes, in the order in which they appear on the tax list, and, on or before the fifteenth day of September thereafter, shall notify each of the delinquents by mail that unless such taxes are paid on or before the fifteenth day of October of that year the taxes will be placed in the hands of the sheriff for collection.