DISTILLATION. The art of obtaining in a separate state, by the appli cation of heat, the more volatile parts of bodies ; but the term is generally limited to signify the separation of volatile liquids, for when the volatile product is obtained from a solid, and assumes a solid form, the operation is termed sublimation. In the distillation of liquids the most volatile parts rising in vapour first are conducted to variously disposed refrigerators, usually composed of metal, and surrounded with cold water, which, abstracting a portion of heat from the vapour, it becomes condensed, and assumes a liquid form. One of the principal applications of the art of distillation is the preparation of spirituous liquors, which is usually divided into two branches. The first, termed distillation, consists in separating the spirituous parts of fermented liquors, mixed with a large portion of water, from the fixed or nonvolatile parts; and in the latter branch, termed rectification, the spirit is concentrated and purified principally by means of redistillation. Having already treated largely upon the various methods of effecting this, under the head ALCOHOL, we shall in this place limit ourselves principally to the description of the preparatoryprocess of distillation, together with some of the most approved apparatus employed therein.
In London and its neighbourhood the process of forming the wash for distillation is the same as in brewing for beer, except that no hops are used, and that instead of boiling the wort they pump it into coolers, and afterwards draw it into backs, to be then fermented with yeast. During the fermentation, considerable attention should be paid to the temperature of the liquid, which should be steadily maintained at about 700 Fahr., and the fermentation is continued until the liquor grows fine and pungent to the taste, but not so long as to allow acetous fermentation to commence. In this state the wash is put into the still (of which it should occupy about three-fourths), and distilled with a gentle fire as long as any spirit conies over, which is generally until about half the wash is consumed. The form of the common still is too well known to need any particular description. It generally consists of a large boiler made of copper, and fixed in masonry over a fire-place. The boiler has a head, or capital, as it is called, which is of a globular form, to which is soldered a neck, forming an arch curved downwards, and fits into what is called the worm : this is a long tube, made generally of pewter, of a gradually increasing diameter ; it is curled round in a spiral form, and enclosed in a tub, which is kept filled with cold water during distillation. That celebrated philosopher and mechanic,
the late Mr. Watt, having ascertained that liquids boil in vacno at a much lower temperature than when under the pressure of the atmosphere, endeavoured to turn this circumstance to advantage in distillation, under the ides that less fuel and also less water for condensation would be required ; but found, by experiment, little or no advantage in this respect, the latent heat of the vapour being nearly the same, whether formed in vacuo or under the pressure of the atmosphere. The idea of distillation in vacuo was subsequently taken up by Mr. Tritton, as affording a means of preventing any empyreumatic flavour being imparted to the spirit by the burning of any matter contained in the still, as • heat considerably less than 212° Fahr. is sufficient to cause the wash to boil rapidly in vacuo. The annexed diagram exhibits a section of Mr. Tritton's apparatus for distilling in vacuo. A is the body of the still ; B is a water bath, into which the body of the still is immersed; C is the head or capital ; D the neck of the same, which, curving downwards, is connected with a pipe that enters the condensing vessel E ; F is a refrigeratory or close vessel, con taining cold water, for converting into liquid the spirituous vapours, which, having been raised in the still, are contained in the vessel E. From the bottom of the vessel E a pipe issues, for conveying the liquid and the vapour not yet condensed into vessel G, which being surrounded with cold water contained in the vessel 11, acts also as a refrigeratory, and reduces the whole of the remaining vapour into a liquid state. I is an air pump for effecting a vacuum in the vessels AEG; K is a stop-cock for cutting off the commu nication between the vessels E and G, when the contents of G are drawn off by the cock M, by which means a vacuum is preserved during that operation in the vessel E and the still A. L is an air cock, to admit air into the vessel G, to allow the contents to run out at M ; N is the discharge cock to the still A. It will be seen that the greatest heat to which the matter in the still can be subjected can never exceed 212° Fahr. ; but upon the pressure of the atmosphere being removed by means of the air-pump, the dis tillation is effected at the low temperature of 132° Fahr., by which means all injury to the flavour of the spirit, by carbonization of the matters contained in the still, is entirely avoided.