In its course downwards the wash is met by the steam passing up through the perforations, and the whole of the spirit which it contains is thus converted into vapor. As soon as the chamber _B_ is nearly full of the spent wash, its contents are run off into the lower compartment by opening a valve in the pipe _V_. By means of the cock _E_, they are finally discharged from the apparatus. This process is continued until all the wash has been pumped through. The course taken by the steam will be readily understood by a glance at the figure. When it has passed through each of the chambers of the analyzer, the mixed vapors of water and spirit pass through the pipe _i_ into the rectifying column. Ascending again, they heat the coiled pipe _m_, and are partially deprived of aqueous vapors by condensation. Being thus gradually concentrated, by the time they reach the opening at _w_ they consist of nearly pure spirit, and are then condensed by the cool liquid in the pipe, fall upon the partition and are carried away by the pipe _y_ to a refrigerator _W_. Any uncondensed gases pass out by the pipe _R_ to the same refrigerator, where they are deprived of any alcohol they may contain. The weak liquor condensed in the different compartments of the rectifier descends in the same manner as the wash descends in the other column; as it always contains a little spirit, it is conveyed by means of the pipe _S_ to the vessel _L_ in order to be pumped once more through the apparatus. =The condensed spirit= gathered over the plates _v_ passes out through the pipe _y_ to the condensing worm _T_. If any vapors escape the condensing plates they pass into _R_ and are condensed in the worm _T_ also. From worm _T_ the spirit flows into a suitable receiver _Z_. Before the process of distillation commences, it is usual, especially when the common Scotch stills are employed, to add about one lb. of soap to the contents of the still for every 100 gallons of wash. This is done in order to prevent the liquid from boiling over, which object is effected in the following way: The fermented wash always contains small quantities of acetic acid; this acts upon the soap, liberating an oily compound which floats upon the surface. The bubbles of gas as they rise from the body of the liquid are broken by this layer of oil, and hence the violence of the ebullition is considerably checked. Butter is sometimes employed for the same purpose. Figs. 19 and 20 show a diagrammatic section and a plan of a still used for thick mashes which are liable to burn. This comprises a circular chamber _B_ supported over suitable heating means, having on its bottom a series of concentric partitions _b_ which divide the bottom of the chamber into shallow channels for the mash. Running diametrically through the chamber is a partition. [Illustration: FIG. 19.--Rotary Current Still.]