Entering by the pipe t, Fig. 15, the undistilled liquid or "wash" is distributed over a perforated plate y y, and falls in drops into the condenser E, where it is heated by contact with the coil S containing the heated vapors. The condenser is divided into two compartments by a diaphragm X which is pierced with holes at its lower extremity;
through these holes the wash flows into the second compartment, and passes out at the top, where it runs through the pipe h, into the top of the column C.
The vapors are made to traverse the coil S, which is kept at an average temperature of 122°F., in the right hand compartment, and somewhat higher in the other. They pass first through J into the hottest part of the coil, and there give up much of the water with which they are mixed, and the process of concentration continues as they pass through the coil. Each spiral is connected at .the bottom with a vertical pipe by which the condensed liquors are run off; these are conducted into the retrograding pipe p p. Those which are condensed in the hottest part of the coil, and are consequently the weakest, are led by the pipe L into the third vessel in the column D, Fig. 16, while the stronger or more vaporized portions pass through L into the fifth vessel. Stop-cocks at m, n, o regulate the flow, of the liquid into these vessels, and consequently also the strength of the spirit obtained.
Lastly, as the highly concentrated vapors leave the coil S at R, they are condensed in the vessel F, which contains another coil. This is kept cool by a stream of liquid flowing from the reservoir H into the smaller cistern G from which a continuous and regular flow is kept up through the tap v into a funnel N and thence into condenser F. It ultimately flows into condenser E through pipe t, there being no other outlet. The finished products run out by pipe x into suitable receivers.
It will be seen that the condenser E has two functions. First it condenses the alcoholic vapors before transmitting them to the final condenser F, rejecting and sending back those vapors which are not highly enough vaporized. Second it heats the wash intended for distilling by appropriating the heat of the vapors to be condensed. Thus two birds are killed with one stone. It will be noticed that the same result is accomplished in the columns C and D. This is the principle of all modem stills.
Another form of still which is very analogous to that last described is Coffey's apparatus, shown in Fig. 18, and is the immediate prototype of the stills used to-day in all but the simplest plants.
It consists of two columns, C the analyser, and H the rectifier, placed side by side and above a chamber containing a steam pipe b from a boiler A. This chamber is divided into two compartments by a horizontal partition a pierced with small holes and furnished with four safety valves, e e e e. The column C is divided into twelve small compartments, by means of horizontal partitions of copper, also pierced with holes and each provided with two little valves f. The spirituous vapors passing up this column are led by a pipe i to the bottom of the second column or rectifier. This column is also divided into compartments in precisely the same way, except that there are
FIG. 18.—Coffery's Rectifying Still.
FIG. 18.—Coffery's Rectifying Still.
fifteen of them, the ten lowest being separated by the partitions, which are pierced with holes. The remaining five partitions are not perforated, but have a wide opening as at w, for the passage of the vapors, and form a condenser for the finished spirit. Between each of these partitions passes one bend of a long zig-zag pipe m, beginning at the top of the column, winding downwards to the bottom, and finally passing upwards again to the top of the other column, so as to discharge its contents into the highest compartment. The apparatus works in the following way: The pump Q is set in motion, and the zigzag pipe m then fills with the wash or fermented liquor until it runs over at n into the highest compartment of column C. The pump is then stopped, and steam is introduced through b, passing up through the two bottom chambers and the short pipe F into the analyzing column, finally reaching the bottom of the other column by means of the pipe i. Here it surrounds the coil pipe m containing the wash, so that the latter becomes rapidly heated.
When several bends of the pipe have become heated, the pump is again set to work, and the hot wash is driven rapidly through the coil and into the analyzer at n. Here it takes the course indicated by the arrows, running down from chamber to chamber through the tubes h until it reaches the bottom; none of the liquor finds its way through the perforations in the various partitions, owing to the pressure of the ascending steam.
As the liquid cannot pass through the holes in the partitions it can only pass downward through the drop-pipe tubes h. By this means the mash is spread in a thin stratum over each partition to the depth of the seal g and is fully exposed to the steam forcing its way up through the holes, the alcohol it contains being thus volatilized at every step.
In its course downwards the wash is met by the steam passing up through the perforations, anal 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.
The mash passes from a tank as A by a passage a to an opening on one side of the central portion and into the outside channel b. The current of
liquid passes along the outer channel until it is deflected by the central partition into the next interior channel b and so on until it arrives at the center when it passes through the central partition into the other half of the chamber. Here it passes around back and forth and gradually outward to the outermost channel from which it passes off through an adjustable gate in outlet c. By adjusting this gate, and a gate or cock in inlet passage a, the passage and consequent depth of the liquid in the channels may be regulated. The vapor rising from the mash is carried over to a condenser through pipe D. In order to keep the mash from burning a chain g is rotarily reciprocated along the channels by means of the bar G, the gear E and the crank shaft e. Various modifications of this construction have been devised. The advantage of the still lies in submitting the mash in a thin current to the action of the heat, and the consequent rapid vaporization.
Every distillation consists of two operations: The conversion of liquid into vapor, and the reconversion of the vapor into liquid. Hence perfect equilibrium should be established between the vaporizing heat and the condensing cold. The quantity of vapor must not be greater or less than can be condensed. If fire is too violent the vapors will pass out of the worm uncondensed. If
the fire is too low the pressure of the vapor is not great enough to prevent the entrance of air, which obstructs distillation. As a means of indicating the proper regulation of the fire, the simple little device shown in Fig. 21 may be used.
This consists of a tube of copper or glass having a ball B eight inches in diameter. The upper end E of the tube is attached to the condensing worm. The lower end of the tube is bent in U-shape; the length of the two bends from b to outlet is four feet. The ball has a capacity slightly greater than the two legs of the bend.
Normally the liquid in the two legs will stand at a level. If, however, the fire is too brisk the vapor will enter the tube and drive out the liquor at d, and thus the level in the leg C will be less than in FIG 21.— Indicator for regulating the Distilling Fire. the leg D. If, however, the fire is low, the pressure of vapor in the worm will decrease and the pressure of the outside air will force down the liquid in leg D and up leg C into the ball.
A more perfected device but operating on the same principle is shown in Fig. 26.
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.
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