In order to measure the output of the still, there is attached thereto a gauge glass (_J_ in Fig. 22), a diagram of which is shown in Fig. 27. This consists of a jar _A_ connected at its lower end at _b_ by an annular passage _B_ to a chamber _E_ from which proceed the taps _F_. Centrally through the passage _B_ passes a tube _c_ connected at its lower end to the pipe _C_ leading from the condenser. The tube _C c_ projects upward into the jar _A_ and is open at its upper end. Now the opening _b_ is of a certain size and it is obvious that it will carry off a certain amount of liquid when running full or the amount allowed to flow out by the exit tap _F_. If now, more than that quantity of alcohol is produced, the alcohol will rise in the jar _A_ until the rate of inflow and outflow is equal. If, however, the still is producing less than that quantity then the level of liquid in _A_ will gradually drop. Hence, by observing the level of the liquid in _A_ and its constancy or variation in level, it is possible to tell precisely how much alcohol is running per hour and if the rate is steady. The jar _A_ is provided with a cap _G_ whereby an alcoholometer may be inserted into tube _c_ for the purpose of testing the strength of the liquor. The taps _F_ are for the purpose of collecting the first runnings, the pure alcohol and the last runnings or "feints." These principles are also embodied in the apparatus designed by the Vulcan Copper Works Co., of Cincinnati, and illustrated in Fig. 28. The apparatus comprises the still, a wash heater and a condenser. The still is composed of a series of chambers from 12 to 24, the internal construction of which is shown in Fig. 29. Each chamber consists of a peculiarly perforated plate _A_, a drop pipe _B_, a seal _C_, into which the drop pipe from the plate above projects, and a central standard _D_. Returning now to Fig. 28, at the bottom of the column is a manifold _E_, with pipes _F_ and _G_ whereby either exhaust or live steam may be admitted. _H_ designates the discharge or slop valve, controlled by a float _I_ whereby a constant level of slop or spent wash is kept in the bottom chamber. [Illustration: FIG. 28.--Continuous Distilling Apparatus, with External Tubular Condenser. (_To face page 72_)] To the right of the column is seen the slop tester _J_ and hydrometer _L_, whereby the spent wash may be tested to see if the spirit is being properly extracted. The steam pressure is indicated by means of a float _N_ contained within a vessel _M_, a tally weight moving against a scale _K_, showing the pressure of steam entering through pipe _O_ and acting against water contained in vessel _M_. Each chamber is provided with a manhole plate _P_, and a try-cock _Q_, whereby the operation of each chamber may be tested. _R_ is a gage glass to show the level of the slop in the bottom chamber.