CHAP. XXIII.Of Rectification.
Thereare several Methods of performing this Operation; though some, and indeed those in general practiced by our Distillers, hardly deserve the Name; because,instead of rectifying, that is freeing the Spirit from its essential Oil and Phlegm, they alter the natural Flavour of the Spirit that comes over in the Operation.
The principal Business of Rectification is to separate the Spirit from the essential Oil of the Ingredient, which is very apt to adhere strongly to the Spirit. And in order to this, Care should be taken in the first Distillation; that is, the Spirit, especially that from Malt, should be drawn by a gentle Fire, by which means great Part of the essential Oil will be kept from mixing with the Spirit; for Experience has abundantly proved, that it is much easier to keep asunder, than to separate them when once mixed.
But as it is almost impossible to draw low Wines without the Spirit being in some Measure impregnated with the essential Oil, it is absolutely necessary to be acquainted with some Methods of separating the Spirit from the Oil, and also of freeing it from its Phlegm. The best Methods of doing this to Perfection, are Re-distillation and Percolation.
In order to rectify low Wines, they should be put into a tall Body or Alembic, and gently distilled inBalneum Mariæ; by thismeans a large Proportion, both of the Oil and Phlegm will remain in the Body. But if the Spirit should be found, after this Operation, to contain some of the essential Oil, it must be let down with fair Water, and re-distilled in the same gentle Manner. And thus it may be brought to any Degree of Purity; especially if in the working the Spirit be suffered to fall into a proper Quantity of clear Water, and the Spirit afterwards rectified to the Height proposed. The same Method should be used in freeing Proof Spirit, or even Alcohol, from this Oil; namely, by letting it down with clean Water to the Strength of low Wines, and re-distilling it inBalneum Mariæ. But it must be remembered, that it is much more difficult to cleanse Alcohol, or Proof-Spirit than low Wines, because the Oil is more intimately mixed with the two former than with the latter. This Oil may however be separated from Proof-Spirit, &c. by the Method already proposed, especially if it be previously filtrated through Paper, thick Flannel, Sand, Stone,&c.
But this Method, though it effectually answers the Intention, is generally rejected by our Distillers, because of the Slowness of the Operation; and others substituted in its stead, though instead of freeing the Spirit from the Oil, they only abolish the naturalFlavour of the Spirit, and make a more intimate Mixture between the Particles of the Spirit, and those of the essential Oil.
It is impossible to enumerate all the Methods practised by Distillers, as almost every one pretends to have a secret Nostrum for this Purpose. The principal Methods in use for rectifying Malt-Spirits, are however reducible to three, namely, by fixed alcaline Salts, by acid Spirits mixed with alcaline Salts, and by saline Bodies, and flavouring Additions.
The Method of rectifying by alcaline Salts is thus performed. To every Piece of Proof Spirit, add fourteen Pounds of dry Salt of Tartar, fixed Nitre, or calcined Tartar; lute on the Head, and distil, by a gentle Heat, but be very careful to leave out the Faints. By this Method a large Proportion of the fœtid Oil will be left in the Still; and what comes over with the Spirit will be greatly attenuated. But this Operation is generally performed in a very different manner; for, instead of distilling the Spirit in a gentle and equable manner, the Still is worked in its full Force; by which means the Oil, which should have remained in the Still, is driven over, and intimately mixed with the Spirit; and, consequently, the whole Operation frustrated,and the Spirit rendered much harder to cleanse than it was before.
But even when the Operation is performed according to the Rules of Art, it is far from being perfect; for it is well known, that Part of the fixed Salts become volatile in the Operation, pass over the Helm, and intimately mixes with the essential Oil still contained in the Spirits: by this means the Oil becomes more perfectly united with the Spirits, and consequently much harder to be separated by repeated Distillations. Nor is this all, for the Still being worked in its full Force, the bitter Oil of the Malt, formed into a kind of liquid Soap in the Still, by means of the alcaline Salt, is brought over the Helm with the Faints, and suffered to mix with the Spirit, whereby it is rendered almost as nauseous and ill-tasted as before the Operation. Besides, if this Operation were performed in its utmost Perfection, it would never answer the Intention; for the alcaline Salt destroys the Vinosity of the Spirit; and consequently deprives it of one of its most valuable Properties. Our Distillers are well acquainted with this Defect in the Operation, and endeavour to supply it by an Addition of Acids. This is what we call the second Method by Alcalies and Acids.
The Operation of rectifying by the Method of fixed Alcalies and Acids is the same as that above described; the Spirit is drawn over from fixed Alcalies as before; but in order to mortify the Alcali in the Spirit, and restore its Vinosity, a proper Quantity of some acid Spirit is added. Various kinds of Acids are used on this Occasion; but principally those of the mineral Kind, because of their Cheapness; as Oil of Vitriol, Spirit of Nitre, Oil of Sulphur, and the like. We would, however, caution a young Distiller from being too busy with these corrosive Acids, the sulphurous Spirit of Vitriol, dulcified Spirit of Nitre, or Mr.Boyle’s acid Spirit of Wine well rectified, will much better answer his Purpose.
The third Method of Rectification is that by saline Bodies, and flavouring Ingredients. There is no Difference in the Operation between this and the two foregoing Methods; fixed alcaline Salts, common Salt decrepitated or dried, calcined Vitriol, Sandiver, Allum,&c.is put into the Still with the low Wines, and the Spirit drawn over as before. When the Quantity is drawn off, the flavouring Ingredients are added to give the Spirit the Flavour intended. But as the Spirit is not by this means rendered sufficiently pure, the disagreeable Flavour ofthe Spirit generally overpowers that of the Ingredients, whereby the whole Intention is either destroyed, or a compound Flavour produced, very different from that intended.
Some Distillers, instead of alcaline Salts, use quick Lime in rectifying their Malt Spirit; this Ingredient cleanses and dephlegmates the Spirit considerably; but like that rectified from alcaline Salts, it requires an alcaline Disposition, and also an nidorous Flavour. Acids, therefore, are as necessary to be mixed with those Spirits rectified with quick Lime, as with those rectified with an alcaline Salt. If Chalk, calcined and well purified animal Bones,&c.were used instead of quick Lime, the Spirit would have a much less alcaline or nidorous Flavour; and, consequently, the flavouring Ingredients might be added to it with more Success than can be expected from a Spirit rectified from alcaline Salts.
But, perhaps, if neutral Salts were used instead of the alcaline ones, the Spirit might be rendered pure, without contracting an alcaline Flavour; soluble Tartar might be used for this Purpose, though the Spirit acquires from hence a little saponaceous Flavour. Dr.Coxhas mentioned another Method for this Purpose, namely, to deprive the volatile Salts of their Oil, by rendering them neutral with Spirit of Salt, and afterwards subliming them with Salt of Tartar: The Acid may be varied if the Spirit of Salt should not be found so well adapted to the Purpose as could be wished: But fine dry Sugar seems the best adapted to the Purpose of rectifying these Spirits; as it readily unites with the essential Oil, detains and fixes it, without imparting any urinous, alcaline, or other nauseous Flavour to the Spirits rectified upon it.
Thus have I considered the principal Methods used by our Distillers in rectifying their Spirits; and shall conclude this Chapter with remarking, that there is no other Way of rectifying to Perfection besides what we first laid down, namely, by gentle Distillation. But then it must be remembered, that the whole Process must be of a Piece: We mean, that the first Distillation from the Wash must be performed in a gentle manner; for otherwise the essential Oil will be so intimately blended with the Spirit, as not to be easily separated by Re-distillation. Another good Property attending this Method is its Universality; all kinds of Spirits, from whatever Ingredients extracted, require Rectification; and this is adapted to all kinds.