It is obviously impossible to present in the small compass of this book a description of all the varieties of stills used, but these which have been described illustrate the principles on which all stills are constructed and were chosen for their simplicity of construction and clearness of their operation. The principle of their operation is exactly the same as the more modern forms now to be described. CHAPTER IV. MODERN DISTILLING APPARATUS. In the previous chapter we have given a description of small, simple stills, such as were used until late years, and which are yet used in many localities where distilling is carried on on a small scale. We will now describe the principle features of more complicated and elaborate apparatus. All modern distilling apparatus for the production of a high grade of alcohol is based upon the principle set forth in the description of the Coffey still; that is, upon using a distilling column and a concentrating column, wherein the "wash" or mash fermented as described, passes over a series of plates or other obstructions in contact with an ascending column of heated vapor. This heated vapor extracts the alcohol from the wash, or from the low wines of the concentrator, and is continually strengthened during its journey until it passes off to a condenser as a vapor very rich in alcohol. The converse of this is true with the wash, which in its downward course is gradually deprived of its alcohol until it finally passes off at the bottom of the column. [Illustration: FIG. 22.--Diagramatic View of Column Still and Accessory Apparatus. (_To face page 64_)] Fig. 22 is illustrative of the general form and arrangement of such a column and its adjuncts; the details, however, will vary with each make of still. In this the "column" consists of a casing really continuous but divided into two portions--the distilling portion _A_ and the rectifying portion _B_. The operation is alike, however, in principle in both portions. [Illustration: Cross-Section of Fig. 23.] [Illustration: FIG. 23.--Distilling Plate.] The wash by means of a suitable pump is forced into an overhead tank or concentrator _G_ where it is warmed by the hot vapors as will be later described. It passes around the interior of the concentrator in a coil _c_ and then passes off by a pipe _a_ to the uppermost plate of the distilling portion _A_ of the column.