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Process of Distillation. In working the still, the feints, if any, remaining from the previous distillation, having been removed to the wash reservoir, are reduced with water to about 85 or 90 per cent. underproof, that is, to an equality in point of strength, as nearly as can be judged, with the wash about to be distilled, and the reservoir is filled up with wash from the wash-charger. High pressure steam, of about five pounds to the square inch, is then admitted into the Analyzer from the boilers.
When a considerable quantity has passed over into the Rectifier, the mixed wash and feints are allowed to flow from the reservoir through the serpentine pipe in the Rectifier to the Analyzer-by which the temperature is brought nearly to the boiling point—where, falling upon the upper diaphragm, they first meet with the steam from the boilers, which is blowing with great force upwards through the holes in the diaphragms, and prevents by its pressure any of the wash from passing through the perforations. Flowing along the diaphragm to its lower end, the wash passes down the dropping tubes, overflows the shallow pans on the next diaphragm, moves along this to the dropping tubes at the opposite end, and falls through to the diaphragm beneath, and in this way is made to flow over every diaphragm to the bottom-the quantity being so regulated as to maintain a uniform stratum not exceeding about an inch in depth.
In its passage to the bottom of the column, the wash is subjected to the continuous action of the steam forcing its way through the perforations in the diaphragms, and by this means its temperature is rapidly brought to and kept at the boiling point, and the alcoholic vapour liberated.
The alcoholic vapour, combined with a large amount of aqueous vapour from the steam and wash, ascends, and passes over by the line-arms to the bottom compartment of the Rectifier as low-wines vapour, at a pressure of about two pounds to the inch. Ascending this column it fills each compartment successively by passing through the holes in the diaphragms, where it is continually subjected to the refrigerating powers of the cold wash flowing through the serpentine pipes.
The impure watery portion being vaporized only at a high temperature, is first condensed into a liquid, and falling upon the diaphragms flows downwards to the bottom frame, while the spirit vapour, which requires a much lower temperature for its condensation, is gradually ascending, gaining in strength, and freeing itself from the feints and impurities.
Thus, while in a state of vapour, the spirit is constantly subjected to this rectifying action, until it is obtained of the required purity and strength, the latter averaging from about 63 to 67 per cent. overproof, as indicated by the glass beads at the sampling apparatus, when the cock of the spirit pipe is opened and the spirit allowed to pass away to the refrigerator.
During this process the impure watery portion—now termed feints—is continually falling to the bottom of the Rectifier, and flowing through the syphon.pipe to the hot-feints receiver, whence it is pumped up into the Analyzer, and again subjected to the powerful action of the steam. In this manner the operation is continuously carried on, wash flowing in and spirit passing off to the receiver.
When the wash has reached the lower frame of the Analyzer it is entirely deprived of its alcohol, and is then allowed to flow away to the spent-wash reservoir.
It may be remarked that the serpentine pipes above the spirit sheet are employed for condensation purposes only, the rectifying process being confined to the compartments below this sheet.
From the foregoing description it will be seen, that the Analyzer is employed to separate the low wines from the wash, and the Rectifier to separate the spirit from the low-wines, and purify it by repeated rectifications ; also, that both columns are in reality Analyzers, or separators, but act on opposite principles, the action of the Analyzer depending on the addition, and that of the rectifier on the abstraction of heat. Thus, in the Analyzer, the low-wines vapour is evolved and separated from the wash by the high temperature imparted to it by the steam ; whilst in the rectifying column the spirit is separated from the low-wines vapour, by the low temperature of the cold wash which condenses the watery portion of the vapour into a liquid.
The working of the still is regulated by an attendant, who, placing himself in front near the spirit sheet, where he has the sampling apparatus, tempering pipe, &c., at his command, and the mercurial syphon.gauges immediately under his inspection, constantly tries the temperature of the interior of the still by that of the wash passing through the serpentine pipes over the spirit sheet ; from long practice ho is enabled to do this by placing his open hand upon the bends of the pipes, by which he readily discovers the least increase in the temperature of the wash circulating through them. This he can reduce either by opening more widely the cock on the wash-pipe, thus giving a greater supply of wash, or by opening the cock on the tempering pipes, and allowing cold water to mix with the wash, which not only reduces the heat of the water, but also that of the interior of the still.
The serpentine water pipes in the three upper frames of the Rectifier are intended for the more effectual condensation of any spirit vapour that has reached this part of the still, the water being of a much lower temperature than the wash. In flowing through these pipes to the jacket-pipe at the bottom of the Analyzer, the temperature of the water is much increased, and in passing through the jacket it absorbs an additional large amount of heat from the spent-wash, by which the temperature is very considerably increased. This heated water is consequently now employed to feed the steam boilers.*
When the distilling process is drawing to a close, and the supply of wash is cut off, the Rectifier contains a very large amount of feints vapour, which it is found far more economical to distil at a high temperature as strong feints, than to continue to rectify for spirits ; even to work it off as strong feints would occupy a considerable time—from one to two hours, according to the quantity. To economise this time, some distillers have adopted a method of discharging the whole of the contents of the Rectifier into the feints receiver instead of working it off in the usual manner.
This is effected by having a branch pipe with a cock, attached to the syphon pipe forming the communication between the bottom of the Rectifier and the hotfeints receiver, in which case the syphon pipe must also be fitted with a cock to cut off the communication with the hot-feints receiver. The branch pipe connects the Rectifier with a refrigerator and the usual feints receiver, and the still is discharged by shutting off the steam from the Analyzer, and allowing a strong stream of cold water to flow through the pipes in the Rectifier to the Analyzer. The communication with the hot-feints receiver being closed, and that with the refrigerator opened, the condensed feints immediately fall to the bottom of the still and flow away to the refrigerator and feints receiver.
* At one of the large distilleries in Ireland the experiment was tried and carried out, for a consider able period, of introducing cold water into the serpentine pipe in four of the frames next below the spirit sheet, by disconnecting the serpentine pipe at the spirit sheet, and connectivg it with that in the fifth frame below, to provide for the continuous flow of wash, and also connecting the pipe in the intermediate frames with a water cistern. It was considered that by more rapidly cooling the spirit vapour at a lower temperature in this manner, a spirit of higher strength and better quality might obtained, but the experiment does ot appear have answered the distiller's expectations.
By this method the still is rapidly discharged, a great saving of time and fuel effected, and the feints do not require to be reduced in strength for the next operation.
The Fusel Oil, or Oil of Grain, is a rather troublesome bye-product to the distiller in the course of his operations. It is formed along with the alcohol in the fermentation of grain, under circumstances which are not fully understood, neither has the quantity produced, in proportion to the spirit, been ascertained ; but it may be here stated, as a rough approximation, that, at four of the large distilleries in the neighbourhood of London, the quantity of fusel oil separated from the feints, in six months, in the year 1856, was 12,366 gallons, the spirits distilled being 2,685,682 proof gallons, and the oil averaging .46 per cent. of the spirit ; but the proportion does not appear to be at all uniform, as the particulars of the above statement will show: thus
Fusel oil has a great affinity for alcohol, and is freely soluble in that substance. Upon the addition of a large amount of water this affinity is overcome ; the oil then readily separates from the spirit, and floats on the surface ; it also separates to a considerable extent from weak feints upon the liquid being allowed to remain undisturbed for a time.
A process has lately been introduced of remoring the oil whilst the operation of distilling is proceeding. The hot feints are allowed to flow from the bottom of the Rectifier to a tall, upright vessel, of small diameter, which they enter near the bottom. During the process of distillation this vessel is maintained nearly full; the hot feints being very weak, the oil readily separates, and from its comparative levity rises to the surface, while the feints, tolerably free from oil, pass away by a pipe fixed in the side of the vessel, to the hot-feints receiver; as the oil accumulates in the vessel it is drawn off either by a small syphon-tube, or by a cock at the side.
Fusel oil is becoming of some importance to the pharmaceutical chemist from its ready convertibility, when pure, into valerianic acid, simply by oxidation, the latter being much used in preparing the valerianates of the metals, particularly that of zinc, for medical purposes.
The oil is made serviceable in some dis. tilleries for illuminating purposes, and as a lubricant for machinery, but its odour is extremely disagreeable and oppressive; it is also employed in preparing imitation of pine apple, jargonelle peur, and other fruit farourings, as a solvent fir resins.
Table showing the boiling points of wash or water containing various proportions of alcohol, and also the proportion of alcohol in the vapour evolved from such liquids.
Plato 2-Fig. 1. Analyzer, or Analyzing Column, front view.
2. Analyzer, side view, having side of the lower frames removed,
showing the arrangement of the diaphragms, tubes, &o. 3. Rectifier, or Rectifying Column, front view. 4. Rectifier, side view, having part of the lower frames removed to
show the interior.
Plate 3-Fig. 5. A Frame of Analyzer, with diaphragm, tubes, &c.
6. A Frame of Rectifier, with diaphragm, serpentine pipe, &o.
Plate 4-Fig. 8. Exhibits the arrangement of the serpentine pipe «G” in three
frames of the Rectifier, the dotted line marking the outline of the frames.
The letters refer to all the figures. A Line-arms, for conveying low-wines vapour from Analyzer to Rectifier. B Steam pipe, from steam boilers to Analyzer. C Spent wash pipe, from Analyzer to spent wash resorvoir, surrounded by a
jacket C° for heating water. D Dropping tubes. D' Sballow pans, into which the dropping tubes enter. D” Valves. E Man-doors. F Pipe for conveying wash from Rectifier to Analyzer, connected withG Serpentine wash pipe, passing through Rectifier. G' Bend, connecting serpentine pipes in each frame. H Pipe from hot-feints pump and receiver to Analyzer. I Pipe from bottom frame of Analyzer, terminating in mercurial gauge K Pipe for conveying vapour from spent-wash to sampling apparatus Z. L Pipe for conveying low.wines vapour from line-arm to sampling apparatus. M Pipe for conveying spirit from spirit pipe to sampling apparatus Z. N Pipe for conveying water from upper frames of Rectifier to the jacket of
spent-wash pipe. O Pipe to convey water from jacket to steam-boilers. P Diaphragm plates. PSpirit-sheet, and “P”, space between spirit sheet and frame, to allow the
passage of spirit vapour.
Rectifier in a serpentine course (as G).
With respect to the comparative produce of spirits from the different materials made use of by distillers, it may be stated, that on the average
1 quarter of malt will produce from 18 to 19 proof gallons.
19 to 20
11.5 1 cwt. of good molasses
8 1 cwt, of treacle
6.7 It appears, accordingly, that if a quarter of malt yield 18 proof gallons of spirits, it will require 252 lbs. of molasses, and 175 lbs. of sugar to give the same produos,