The Internal Revenue provides that no process of rectification shall be carried on less than 600 feet distant from the distillery, and there shall be no underground or secret passage or pipe connections of any description between the rectifying house and the distillery.

When a spirit is taken to a "rectifying" house the tax is first paid thereon, as has already been described, and the purchaser is allowed, within certain restrictions of the Revenue Department, to do as he pleases with the product. He can mix together two or more spirits, forming what is known as a compound, or he can compound the spirit with other spirits or other substances, just as he sees fit. He may add coloring matter, sugar, spices, prune juice, sherry or any other substance he likes, provided always he is able, by the gauging of the finished product, to account for all the spirit for which he has been charged. Under the law this mixing or compounding is called "rectification."