The principle of compound distillation is well shown in Dorn's apparatus, Fig. 12. This consists of a still or boiler _A_ having a large dome-shaped head, on the interior faces of which the alcoholic vapors will condense. Thus only enriched vapors will pass up through goose-neck _B_ to the mash heater _D_. _C_ is a worm the end of which passes out to a compartment _E_ through an inclined partition _F_. From the compartment _E_ a pipe _e_ leads into the still _A_. An agitator _H_ is used for stirring the mash, so that it may be uniformly heated. A pipe _d_ provided with a cock allows the mash to be drawn off into the still _A_. From the highest point of the compartment _E_ a pipe _M_ leads to condensing coil _K_ in a tub _J_ of cold water, having a draw-off cock _I_. At the exit end of the condensing worm _K_ the tube is bent in a U form as at _L_, one arm of which has a curved open-ended continuation _n_, through which the air in the worm is expelled. The other arm opens into an inverted jar _l_ containing a hydrometer, for indicating the strength of the spirit. The spirits pass off through _m_ into a receiver. In operation the mash is admitted into the heater _D_ through _G_ until the heating tank is nearly filled. A certain amount of mash is then allowed to run into the still _A_ through the pipe _d_. The cock in _d_ is closed and the fire lighted. The vapors from the still are condensed in worm _C_ and the condensed liquid drops down into compartment _E_. Any vapor passing through _B_ and _C_ so highly heated as to be uncondensed in coils _C_ passes through the layer of liquid in compartment _E_, collects in the highest portion of the compartment and passes through pipe _M_ to coil _K_ where it is entirely liquefied. If the liquid in _E_ rises beyond a certain level it passes through pipe _e_ back to the still. Any vapors which may collect in the upper part of _D_ pass into the small bent pipe opening into the first coil of worm _C_. Water for rinsing the heater _D_ may be drawn through cock _s_ from the tub _J_ and warm water for rinsing the still, through pipe _d_ from the heater. Another form of compound still is shown in Fig. 13. In this the still _S_ is divided into an upper and lower compartment by a concavo-convex partition _d_, having at its crown an upwardly extending tube _t_ from which projects side tubes _p_. A pipe _P_ opens above and extends from tube _t_. _C_ is the mash heater and condenser. Connected to the head of the still is a pipe _T_ through which the vapors pass to a condensing coil _f_ formed on the wall of the heater _C_. At its bottom the coil _f_ extends out of the heater, through the water tub _W_ and out to receiver as at _F_. In the heat of this heater is a valve _V_ whereby any vapors which may arise from the heated mash are conducted by pipe _U_ to _T_.