Distillation

“ In the laboratory, distillation is employed for purifying water, for recovering alcohol and ether, and for the preparation, purification, and separation of a great number of bodies. Substances which decompose at their boiling-points can be distilled under reduced pressure. On the large scale distillation is employed in the preparation of potassium, sodium, zinc, mercury; of sulphuric acid, ether, chloroform, carbon bisulphide, essential oils and perfumes; in the purification of coal and wood tar, and the products obtained from them ”

“ The distillation is then started. It involves the formation of two sets of volatile products, namely— (1) combustible gases (including sulphuretted hydrogen and bisulphide of carbon vapour) , which must be led away to avoid nuisance and danger of fire, and (2) a very complex liquid or semi-liquid distillate. This latter is collected in successive fractions, generally in this manner:— (1) as "first runnings," what comes over at temperatures below 105° to 110°C.; (2) as "light oils," at temperatures between 110° and 210°C.; (3) as "carbolic oil," at temperatures between 210° to 240° C. ”

“ The business of distillation, is to separate the more volatile from the less volatile of two bodies. The whole mixture is put into a vessel, under which there is fire: the most volatile liquor begins first to turn into vapour, and rises into a higher vessel, which, being kept cold by water or snow, condenses the evaporated fluid; after it has been condensed, it drops into another vessel. In the experiment that the child has just tried, after having separated the camphire from the spirit of wine by precipitation, he may separate the spirit from the water by distillation. ”

“ The technology of distillation is best studied in relation to the several industries in which it is employed; reference should be made to the articles Coal-Tar, Gas, Petroleum, Spirits, Nitric Acid, &c. ”

“ The whole process of distillation appears, therefore, to be a decomposition by which the pitchy substance is converted into oil, acetic acid, ammonia and charcoal.
I proceeded next to examine the oil. It has a violently pungent taste and smell. It is scarcely heavier than water; so that it sinks in that fluid with difficulty, leaving generally some drops on the surface. It is perfectly soluble in alcohol, in ether, in caustic alkali, in olive oil, and in linseed oil. It will unite neither to naphtha, nor to the recent essential oils, but is soluble in the old ones. ”

“ Operating in a current of carbon dioxide facilitates the process by preventing overheating.
7. Distillation in Chemical Technology.—In laboratory practice use is made of a fairly constant type of apparatus, only trifling modifications being generally necessary to adapt the apparatus for any distillation or fractionation; in technology, on the other hand, many questions have to be considered which generally demand the adoption of special constructions for the economic distillation of different substances. The modes of distillation enumerated above all occur in manufacturing practice. ”

“ This Chapter alone might make a Volume, were we to make a particular Enumeration of all its Parts; but, as we have already observed, we shall confine ourselves to the Distillation of simple and compound Waters, &c.
If we acquit ourselves to the Satisfaction of the Public, we shall enjoy the Pleasure of having treated of one Part entirely new; and, indeed, the only one that has been overlooked.
The Bodies proper for Distillation, are Flowers, Fruits, Seeds, Spices and aromatic Plants.
By Distillation and Digestion, we extract the Colour and Smell of Flowers in simple Waters and Essences. ”

“ Distillation.—The primary object of the distillation of all fermented liquids is that of separating, as far as possible, alcohol from the non-volatile constituents of the wash. In the second place the object of the distiller is to rectify and concentrate the dilute alcoholic liquid obtained by simple distillation. The degree and manner of rectification and concentration vary in accordance with the type of spirit to be produced, and it will be better therefore to discuss methods of distillation under the headings of the different types of spirit concerned. ”

“ In the distillation it is a common practice, especially in Germany, to do away with the condensing worm and to carry a long glass tube from the distilling flask directly into the acid on the receiver. The only inconvenience in this method is the heating of the contents of the receiving flask, but this is attended with no danger of loss of ammonia and the distillate, on account of the high temperature it acquires, is left free of carbon dioxid. Many of these minor changes have tended to simplify the process, but without affecting the principle of the method in the least. ”

“ That of another advertised nostrum is a mixture of mercury and chalk, with a little rhubarb and ipecacuanha.
DISTILLA′TION. The evaporation and subsequent condensation of the vapour of fluids, by means of a still and refrigerator, or other similar apparatus. Dry distillation is a term applied to the distillation of substances per se, or without the addition of water or other volatile fluid. Destructive distillation is the distillation of substances at temperatures sufficiently high to decompose them, by which their elements are separated, or evolved in new combinations. ”

“ It is found from experience, and is readily accounted for by theory, that the lower the temperature at which the distillation is conducted, the stronger will be the product, and the less quantity of oil or other volatile matter will come over along with it. ”

“ When two bodies, of which one is more volatile than the other, or has more affinity to caloric, are submitted to distillation, our intention is to separate them from each other: The more volatile substance assumes the form of gas, and is afterwards condensed by refrigeration in proper vessels. In this case distillation, like evaporation, becomes a species of mechanical operation, which separates two substances from each other without decomposing or altering the nature of either. In evaporation, our only object is to preserve the fixed body, without paying any regard to the volatile matter ”

“ As this takes place in each successive distillation, if we make use of large vessels and a considerable degree of heat, we at last decompose the whole of the oil, and it entirely into water and charcoal. When we employ a slow fire, and especially when we employ a slow fire, or degree of heat little above that of boiling water, the total decomposition of these oils, by repeated distillation, is greatly more tedious, and more difficulty accomplished. ”

“ Distillation proceeds quietly and uniformly, the fire being regulated according to how the ether runs off from the worm. Such uniform distillation is, however, only attained by the use of the sodium acetate in the form of powder, and thoroughly mixing it with the acid. If large pieces of the salt are present or the powdered salt balls together, the formation of ether sometimes takes [Pg 203] place so suddenly that the vapors cannot condense in the cooling apparatus, but escape violently, or if they cannot escape rapidly from the condenser, may even burst the apparatus. ”

“ Whatever the variety of petroleum may be, if exposed for a long time to the air it undergoes a spontaneous distillation, in which gases and vapors, existing or formed, escape, and solid residues are left. ”

“ When Oils are drawn from Seeds, the Operation is performed either by the Balneum Mariæ, or the Vapour Bath.
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We only deliver in this Place, the first Elements of each of these Operations, which will be farther illustrated in the Sequel, when we treat more particularly of these Subjects.
CHAP. XIII.
Of what is procured by Distillation. By Distillation are procured Spirit, Essence, simple Waters and Phlegm.
Spirits are very difficult to be defined. I consider them as the most subtil and volatile Parts of a Body.
All Bodies without Exception have Spirits more or less. ”

“ This operation of turning a fluid into vapour, and then condensing it, is called distillation. For this purpose, the vessel in which the liquor is heated is closely covered with another called the head, into which the steam rises and is condensed. It is then drawn off by means of a pipe into another vessel called the receiver. In this way all sweet-scented and aromatic liquors are drawn from fragrant vegetables, by means of water or spirits. The fragrant part being very volatile rises along with the steam of the water or spirit, and remains united with it 126after it is condensed. ”

“ This process is termed destructive distillation, and the property displayed by coal is common to all vegetable and animal substances; but only coal and petroleum have been used economically in the production of illuminating gas on an extensive scale. The distillation is the most important operation in the manufacture, but it is necessary to remove from the gas, before it is fit for burning, the condensible vapors, as tar, water, etc. ”

“ If we distill either of these more solid substances with a very gentle heat, we obtain naphtha, in which the proportion of the hydrogen to the carbon is increased to a maximum ratio. If the heat is greater, we obtain a substance of a darker colour, in which that ratio is less; and, for this reason, the distillation of asphaltum affords a darker oil than that of petroleum, because its composition cannot be dissolved but in a higher temperature. ”

“ In general, when the substance to be distilled has a vapour pressure of only 10 mm. at 100° C., distillation with steam can be adopted, if the product can be subsequently separated from the water.
When distilling a mixture of partially miscible components a distillate of constant composition is obtained so long as two layers are present, i.e. ”

“ Dry distillation is extremely wasteful even when definite substances or mixtures, such as calcium acetate which yields acetone, are dealt with, valueless by-products being obtained and the condensate usually requiring much purification. ”

“ Of artificial productions the most fruitful and important is provided by the destructive or dry distillation of many organic substances; familiar examples are the distillation of coal, which yields ordinary lighting gas, composed of gaseous hydrocarbons, and also coal tar, which, on subsequent fractional distillations, yields many liquid and solid hydrocarbons, all of high industrial value. ”

“ The product of the distillation is however subjected to a redistillation till about 1⁄5th is come over in the receiver. A concentrated aqueous solution of the oil is thus obtained, and the oil itself, though only in very minute quantities. ”

“ Continue your distillation, increasing your fire from time to time, by slow degrees. These two liquors will continue to come off together: and the nearer the operation draws to its end, the more acid will the aqueous liquor become, and [Pg 461] the thicker and deeper coloured will the Oil grow. At last the Oil will be very thick, and of a deep reddish-yellow colour. When nothing more ascends, unlute your vessels: in the retort you will find only a very small quantity of a charred, light, friable substance. ”

“ The second liquid product of the destructive distillation of coal is the ammoniacal or gas liquor, which consists of water containing ammonia salts in solution, partly condensed from the hot gas, and partly added to wash the gas in the scrubbers. ”

“ After cooling a second time the whole is brought into a distillation flask of about three-quarters of a liter capacity and attached to a condenser [Pg 195] which ends in a vessel containing titrated sulfuric acid. About forty cubic centimeters of sodium hydroxid solution of one and three-tenths specific gravity are added and the stopper at once inserted to prevent any loss of ammonia. To prevent bumping during the distillation some zinc dust is added securing an evolution of hydrogen during the progress of the distillation. ”

“ Where the business is to be entered into on a large scale, to take the products from a considerable section of country and turn them into alcohol to compete in the great markets, the best of apparatus and equipment is not too good, but [190] the person contemplating the mere manufacture of alcohol on a small scale, to serve only a small section, must remember that distillation is really a very simple matter, for years practiced with a most rudimentary apparatus and still so practiced in the country districts particularly in the South. ”

“ In ordinary processes (1) a given quantity of impure alcohol must undergo five rectifications in order that the products composing the mixture (pure alcohol, oils, etc.) may be separated and sold according to their respective quality; (2) the mean yield in the first distillation does not exceed 60 cent.; (3) the loss experienced in distillation amounts, for each rectification, to 4 per cent.; (4) the quantity of essential oils (mixture of the homologues of ethylic alcohol) collected at the end of the first distillation equals, on an average, 3.5 per cent. ”

“ When it is subjected to distillation in a heat sufficient to keep it in a gentle ebullition, an oily looking matter passes over in considerable proportion, which sinks to the bottom of the water into which the tube is inserted. ”

“ For this purpose we may make use of the same apparatus, only substituting for the stoneware retort a glass one, placed in a sand bath. All the globes ought to be perfectly clean and dry. The distillation is to be conducted in the usual way. If we divide the product into thirds, the first yields the feeblest acid, and the third the strongest. We should not push the process quite to dryness, because there remains in the last portions certain impurities, which would injure the flavour of the acid. ”