It is unlawful for any person to purchase any junk from any minor under the age of eighteen years, without receiving from such minor the written authority from the person owning such junk, authorizing him to sell the same, and if the owner of such junk is one other than the parent or parents, or legal guardian of such minor, then in addition thereto the witnessed authority of such parent or legal guardian, and all of such written authority shall be received and placed on file with the person receiving such junk and shall be a part of the record of the transaction subject to inspection by the officials herein named. (Ord. 951 § 4, 1917)