If any person liable for any tax under Sections 737.09 or 737.10 shall ship or transport his products, or any part thereof, out of the City without making sale of such products, the value of the products in the condition or form in which they exist immediately before transportation out of the City shall be the basis for the assessment of the tax imposed in such sections. The City Treasurer shall prescribe equitable and uniform rules for ascertaining such value. (1970 Code Sec. 29-4)