Dr. Arnott, in his work on the Elements of Physics, proposes a mode of distilling or evaporating in vacuo, without the aid of an air pump, by simply establishing a communication between a close distilling or evapo rating vessel, and the top of a water barometer. The principle of this method will be readily comprehended by referring to the annexed diagram and its accom panying explanation. a is the evaporating vessel or still, the neck of which communicates with a strong vessel b, forming the top of the barometer ; from the under side of b proceeds a tube, plunging in a small vessel d, situated 36 feet below the bottom of & The cocks at d and e being shut, the vessel b and the descending pipe are to be filled with water through a cock c at the top ; then this cock being shut, and the cock at d opened, the water will sink down out of the vessel b until the column in the tube be only 34 feet high, as at f, that being the height which the atmosphere will support. On opening a commu nication between the vessel a and the vacuum in b, the operation goes on as desired, and the steam arising from a may be constantly condensed by allowing a small stream of water to run through b from above, in cases where it is sought to concentrate any liquid in a in vacuo ; but for distillation, where the condensed vapour is the product which is sought, the water must be applied externally to b, by placing that vessel in another vessel g, kept constantly full of water. If the vacuum becomes destroyed by the accumulation of the air extricated in boiling, it may be easily restored by refilling b as at first. Dr. Arnott states that he planned this arrangement as a simple apparatus for the preparation of medicinal extracts, as many watery extracts from vegetables have their virtues impaired or destroyed by a heat of but when the water is driven off in vacuo, the temperature need never be higher than blood heat The doctor further observes, that this plan appears "particularly well suited to the colonies, where air-pumps and nicer machinery can with difficulty be either obtained or managed." The annexed engraving represents Sir Anthony Perrier's improved apparatus for distillation. The object of this invention is to cause the liquid to flow gradually over the heated surface of the body of the still, and during its progress to give out its spirituous vapour, and to maintain a continuous and uninterrupted distillation as long as the supply of liquid is furnished and the fire kept up. Fig. I is a view, in profile, of the section of the still, and Fig. 2 is a plan of the same. The bottom of this boiler is divided by concentric partitions, which stand up, as in Fig. I, sufficiently high to prevent the liquor from boiling over.. These partitions have openings from one to the other at opposite sides, so as to make the course a sort of labyrinth. f is a reservoir of liquor prepared for the operation ; y is a pipe or tube descending from the reservoir, and conducting the liquor to that part of the boiler marked h, which is the commence ment of the race. From hence the liquor flows through the channels, as shown by the bent arrows, progressively traversing the whole surface of the bottom, whereby the full effect of the fire is exerted upon small portions of the liquid, which causes the evaporation to proceed with great rapidity. The residue of the liquid then passes off by the discharge pipe i, which is made to slide, for the purpose of regulating the quantity and depth of fluid in the still ; and this pipe should be in such proportion to the admission pipe, as to cause the perfect distillation of the liquor in its passage to the regulating tube. In the still, as shown at Bg. 1, a set of chains are seen suspended from a bar i i, supported by a centre shaft, which may be put in motion by a toothed wheel and pinion, actuated by a crank or winch. These chains hang in loops, and fall into the spaces between the partitions, for the purpose of sweeping the bottom of the still, and preventing the material operated upon from burning, when of a thick or glutinous nature, as turpentine, syrups, &c.
In the still we are now about to describe, invented by Mr. Frazer, of Houndsditch, the object is the economizing of fuel, and the production of a pure spirit, by a peculiar arrangement of the vessels employed, that shall at the same time be in perfect accordance with the existing excise laws. The wash still, instead of being exposed to naked fire, is immersed in boiling water, the vapour from the former enters the low wine still, where it is condensed ; the wine thus abstracts the heat from the wash, becomes itself vapourized, and is conducted into a refrigemtory ; the first and second distillations are in this manner con ducted together by a continuous process, which will be best understood by a reference to the annexed diagram. a is a supposed steam engine boiler, or other similar vessel, the heat from which boils the wash (or low wine) in the still b. To prevent the liquid from boiling over into the condenser, the neck is formed of the shape shown at i; from hence the vapour passes through a steam tight case e, immersed in a reservoir c, containing either wash or the product of the first distillation, where it becomes partly condensed ; the vapour and condensed liquid then descend through the worm beneath, wherein the condensation is completed and the liquid cooled, which then runs into the closed recipient d underneath. This recipient d therefore contains the weak spirit of the first distillation, called low wines, to re-distil which product it is raised by the pump f, and discharged into the reservoir c, which is, in effect, the low wine still. The liquid in this vessel, as before mentioned, is vapourized by the heat of the vapour from the wash still passing through it; it is afterwards condensed in the refrigeratory g, and finally received into the closed vessel h, where the operation is completed.
The engraving on p. 440 represents the patent distilling apparatus of Mr. Stein; in appearance it greatly resembles those constructed in France upon the plan of Woolf's apparatus ; but the principle of its operation is totally dif ferent, the object being rather to cause a great economy in the consumption of fuel, than to obtain spirits of any required strength at a single operation. The beat absorbed in the conversion of a given weight of water into steam, exceeds greatly that which is required to raise its temperature to the boiling point ; a pound of water converted into steam raising six pounds of water to the point of ebullition. The heat thus developed varies in different liquids, but is in all cases considerable ; and as distillation is ordinarily conducted, this heat is not merely lost, but occasions a considerable additional expense, from the great quantity of water required to reduce the vapour to the liquid state. To obviate these two sources of loss, the patentee has contrived his apparatus, so that one portion of liquid formed into vapour shall be reduced to the liquid form by another portion of liquid, which is evaporated by the heat given out in the condensation. But to convert a fluid into steam, not only a certain quantity of heat is required, but the heat must also be of a certain intensity ; thus, although a pound of steam at 2120, would raise six pounds of water to the boiling point, it would convert no portion of it into steam, as the moment the water had acquired the heat of the steam, it would receive no further portion of heat from it; but if the steam is formed under a pressure exceeding that of the atmosphere, its heat, as indicated by the thermometer, is increased, and consequently it will continue to impart heat to a liquid which has attained the boiling point under a less pressure than the steam employed to heat it. Upon the combination of these two principles, Mr. Stein's apparatus is constructed. Nos. 1, 2, 3, and 4, are four oblong elliptical vessels or stills, two of which are shown in section ; the lowermost halves are enclosed in casings a a, forming thereby steam chambers b b ; each still has a vertical pipe c c c c, terminated by a double passage cock d d, one passage opening into the pipe e, which leads to the worm tub, whilst the other opens a communication from one still to the steam case of the next still, by means of the curved pipes fff ; that from the still 1 leading to the steam case of still 2, and so on in succession. The stills are charged from the pipe g, the quantity admitted being regulated by the floats h; each steam case communicates by the pipes III/ (which are furnished with cocks) with the pipe k proceeding from the boiler. From the lower part of the steam case proceed pipes m tri ; that from still 1 leads to the cistern, which furnishes the steam boiler with hot water, whilst the others may either communicate with one common main n, leading to a refrigerator, or they may each communicate with a separate refrigerator. From the upper part of each steam case proceeds a pipe (shown at 3 and 4) which communicates with a gauge pipe pp, and ter minates in a syphon barometer q g. r r r r are the man holes to each still ; '188 the discharge pipes to the stills, the steam cases being emptied by opening cocks in the pipes ra m leading to the main n. The operation is as follows :— The stills being charged, and the cocks d being open to e, the steam is admitted to each case by the pipes I I leading from the steam pipe k, and is rapidly con densed in the steam case, the air escaping by a pipe not shown in our drawing. When the liquor in the stills has nearly attained the boiling point, the steam is shut off from all the cases except that of I, and the cocks opened to the pipes f, and the main a, being cleared of the condensed water, the cocks on In 3, and 4 are closed. The steam from the boilers (which is under consider able pressure) continues to flow into the case I, and by the heat given out to the liquor in the still, causes it to boil ; the vapour passes into the steam case of 2, and the liquor in 2 condenses the steam in 1, until a common temperature is attained ; then the steam from 1 being no longer condensed, and continuing still to receive heat from the boiler, its pressure, and consequently its temper. ature, increases, and it again gives out heat to the liquid in 2, which cause! it to boil. The vapour from 2 then passes into the steam case of 3, where the same process ensues, and which is subsequently repeated under the still 4, the steam from which passes by the pipe e to the condenser. As soon as the liquids in 2, 3, and 4 begin to boil, the cock on m must be partially opened to allow the condensed spirit to pass by the pipe a to the refrigerator ; yet always retaining a certain portion in the steam case, the height of which may be ascertained by the gauge pipe p, whilst the barometer q q will indicate the pressure of the steam in each steam case. The proper pressures will be best obtained by observation, as it will vary in different liquors during the distilla tion. The person conducting the process must, therefore, pay great attention to the barometer; and to enable him to do this with facility, the gauge pipes and barometer are all ranged in a cluster at the centre of the apparatus. By this mode of distillation, it will be seen that the latent heat of three-fourths of the liquid evaporated is saved, which produces a corresponding saving in the article of condensing water.