It shall be unlawful for any pharmacist to sell at retail any of the poisons enumerated in section 205.5 unless the pharmacist ascertains that the purchaser is aware of the character of the drug and the purchaser represents that it is to be used for a proper purpose and every sale of any poison enumerated in section 205.5 shall be entered in a book kept for that purpose, to be known as a “Poison Register” and the same shall show the date of the sale, the name and address of the purchaser, the name of the poison, the purpose for which it was represented to be purchased, and the name of the natural person making the sale, which book or books shall be open for inspection by the board of pharmacy, or any magistrate or peace officer of this state, and preserved for at least five years after the date of the last sale therein recorded.