Meaning of word “gallon.”

The word “gallon,” when used on or impressed into any container of spirits of turpentine, or when used in an invoice referring to spirits of turpentine in containers of 10 gallons content or less, shall mean a United States standard gallon of 231 cubic inches of turpentine, regardless of any other definitive terms used therewith: Provided, That this shall not apply to the meaning of the words “imperial gallon”, when placed on containers intended for foreign shipment. For the purpose of these regulations a measured gallon of turpentine, or any indicated multiple or fractional part thereof, shall be such quantity when measured at a temperature of not more than 75 °Fahrenheit, and a weighed gallon shall be construed to mean 7.2 pounds of turpentine.