The process of rectification may be carried on in the apparatus shown in Figs. 35 and 36. _A_ is a still which contains the spirit to be rectified; it should be four-fifths full. The condenser _E_ and the cooler _G_ are filled with water. After closing the cocks _L_ and _I_, the contents of the still are heated by steam, which is introduced at first slowly. The vapors of spirit given off pass, by tubes _b_, above each plate _a_, of the series in column _B_, and escape through _C_ and _D_ into the condenser _E_, where they are condensed on reaching the lentils _d d¥_, and return in a liquid state through pipe _f_ and connections _g g¥_ to the upper plates of the column _B_. In these return pipes the liquid is volatilized, and constantly recharged with alcohol to be again condensed, until the water in the condenser is hot enough to permit the lighter alcoholic vapors to pass into the coil _c c c_, without being reduced to the liquid state. When this is the case, the vapors pass through _F_ into the cooler _G_, where they undergo complete condensation. Great care must be taken that the heat is not so great as to permit any of the vapors to pass over uncondensed or to flow away in a hot state; and also to keep up a constant supply of water in the cooler without producing too low a temperature; the alcoholic products should run out just cold. The highly volatile constituents of the spirit come over first, that which follows becoming gradually purer until it consists of well-flavored alcohol; after this comes a product containing the essential oils. The more impure products are kept apart from the rest and re-distilled with the next charge. Some hours generally elapse before alcohol begins to flow from the cooler. The purest alcohol is obtained while its strength is kept between 92∞ and 96∞ Baume, and the operation is complete when the liquid flowing through the vessel marks not more than 3∞ or 4∞ Baume; it is better, however, to stop the still when the backing or "faints" indicate 10∞, because the product after this point contains much fusel-oil, and is not worth collecting. [Illustration: FIG. 36.--Section of Rectifying Still.]